electronics lab manual

Dept. of Electronics St. Peter’s VHSS, Kolenchery

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PRACTICAL RECORD

IIND YEAR MRRTV

Printed and Published by

Dept. of Electronics St. Peter’s VHSS, Kolenchery,

Ernakulam (Dist) Kerala State

Email: [email protected]


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PRACTICAL RECORD

NAME OF THE STUDENT :

CLASS NO. :

REG.NO :

YEAR :

Certified that this is a bona fide record of Practical work of Sri. ……………… ………

……… ……………………………………………. ……Reg. No …………… …………… ………… in the

Year ……………………………..

Date Staff in Charge

Signatures of Examiners

1.External Date

2.Internal


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SAFETY PRECAUTIONS

1. Use wooden chairs and tables while working with electricity.

2. Do not leave any wire or joint naked

3. Do not wear wet clothes while working with electricity

4. Do not disconnect wires by pulling

5. The handles of all tools should be covered with proper insulation.

6. Remember that proper earthing is very much essential for safety.

7. Under any circumstance, do not touch both positive and negative wires at a time.

8. Only a suitable tool should be used for a particular purpose.

9. Always put the switch at positive phase.

10. Always confirm that the circuit is wired correctly before turning on the power.

11. Always hold leads by their insulated areas.

12. Always hold test leads by their insulated areas.

13. When anybody is getting shock, push him through an insulator.

14. All injuries must be immediately taken care of or else it may cause infection.


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INDEX

Expt. no Date Description of Title of Experiment Page. No Remarks

1 AMPLITUDE MODULATOR 8

2 AM DETECTOR 12

3 FREQUENCY MODULATION 16

4 FM DEMODULATION 20

5 LAY OUT OF TRANSISTORISED RADIO RECEIVER 24

6 SUPER HETERODYNE RADIO RECEIVER (WORKING) 26

7 CONVERTOR SECTION OF SHR 28

8 BAND SWITCH CONNECTIONS OF SHR 30

9 IF AND DETECTOR SECTIONS OF SHR 32

10 AUDIO SECTION OF SHR 36

11 TESTING RECEIVER WITH SIGNAL GENERATOR 40

12 IF ALIGNMENT 41

13 RF ALIGNMENT 42

14 TROUBLE SHOOTING BASED ON SYMPTOMS 43

15 TESTING OF RADIO COMPONENTS 44

16 FAULT ANALYSIS OF RADIO RECEIVER 48

17 METER BANDS OF RADIO STATION 49

18 PA SYSTEM INSTALLATION 50

19 DTH SYSTEM INSTALLATION 52

20 STUDY OF TAPE RECORDER AND ITS MECHANISM 56

21 CONTROLS OF TAPE RECORDER 60

22 HEAD CLEANING OF TAPE RECORDER 62

23 HEAD REPLACEMENT OF TAPE RECORDER 66

24 HEAD ADJUSTMENT OF TAPE RECORDER 68

25 MAIN BELT REPLACEMENT OF TAPE RECORDER 70

26 FAULT ANALYSIS OF TAPE RECORDER 72

27 INSTALLATION OF SURROUND SYSTEM (5.1) 78

28 TELEVISION ANTENNA, TXN LINES & BOOSTER 80

29 PATTERN GENERATOR 84

30 TV BROADCAST CHANNELS 88

31 BLOCK DIAGRAM OF TEXLA KIT 89

32 TELEVISION ANTENNA CHECK 89

33 TELEVISION TUNER (TURRET TYPE) 90

34 MONOCHROME PICTURE TUBE SPECIFICATIONS 92

35 TRANSFORMER POWER SUPPLY – TEXLA KIT 94

36 VIDEO IF AMPLIFIER – TEXLA KIT 96

37 SOUND SECTION – TEXLA KIT 100

38 TELEVISION RECEIVER CONTROLS/ADJUSTMENTS 104

39 ICS AND TRANSISTORS USED IN TEXLA KIT 105

40 HORIZONTAL OUTPUT SECTION OF TEXLA TV 106

41 VERTICAL OSCILLATOR AND OUTPUT SECTION 110

42 HORIZONTAL OSCILLATOR 112

43 VIDEO AMPLIFIER AND PICTURE TUBE SECTION 114

44 ICs USED IN DAEWOO KIT – 14” 116

45 OPERATING CONTROLS OF COLOUR TV RECEIVER 118


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46 TV SERVICING INSTRUCTIONS AND WARNINGS 120

47 CHARACTERISTICS OF SOUND 123

48 TROUBLE SHOOTING OF MONOCHROME TV 124

49 FAULT ANALYSIS – TEXLA TV 126

50 STUDY OF CTV RECEIVER – FONDA KIT 134

51 SMPS – FAULT ANALYSIS 138

52 POWER SUPPLY OF FONDA KIT 140

53 ELECTRONIC TUNER 143

54 TUNER SECTION OF FONDA KIT 146

55 SYSTEM CONTROL SECTION – FONDA KIT 148

56 VIDEO IF AND SOUND IF – FONDA KIT 150

57 SOUD OUTPUT SECTION – FONDA KIT 154

58 COLOUR SECTION – FONDA KIT 156

59 CRT DRIVE SECTION – FONDA KIT 160

60 FAULT ANALYSIS – COLOUR TELEVISION 162

61 NECK CONFIGURATION OF CTV PICTURE TUBE 164

62 COLOUR TELEVISION SYMPTOMS 166

63 WHITE BALANCING IN COLOUR TELEVISION 168

64 TECHNICIAN CONTROLS OF COLOUR TV RECEIVER 169

65 PURITY AND CONVERGENCE ADJUSTMENTS 170

66 SERIES VOLTAGE FEED BACK REGULATOR 174

67 UNDERSTANDING VCR 176

68 HEAD CLEANING – VCR 178

69 CD/DVD PLAYER – PARTS 182

70 MOTHER BOARD LAY OUT – CD PLAYER 184

71 SKIPPING CD PLAYER 186

72 REPAIRING SCRATCHED CD/DVD 187

73 FIXING AND MAKING CDs PLAYABLE AGAIN 188

74 HOW TO BUY A NEW CD/DVD PLAYER 189

75 HOW TO PROLONG THE LIFE OF A CD PLAYER 190

76 CLEANING DIGITAL CAMERAS 191

77 VCD PLAYER – INTERNAL SCHEMATIC 192

78 CONNECTING VCD PLAYER AND TV RECEIVER 198

79 CONTROLS OF CD PLAYER 200

80 REMOTE CONTROL OPERATION – VCD PLAYER 202

81 PRECAUTIONS WHEN USING CD PLAYER 210

82 VCD PLAYER TROUBLE SHOOTING 212

83 REPLACING DEFECTIVE TRAY/LOADING MOTOR 216

84 LASER DIODE PROBLEMS 218

85 REPLACING DEFECTIVE SLIDE MOTOR 222

86 REPLACING DEFECTIVE SPINDLE MOTOR 224

87 INTERNAL SCHEMATICS OF VCD PLAYER 226

88 DVD PLAYER 231

89 REMOTE CONTROL AND ITS WORKING 236

90 TV TUNER CARD FOR COMPUTERS 240

91 CABLE TELEVISION SYSTEM 242

92 INSTALLATION OF CCTV NETWORK 244


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Observation

Modulating signal amplitude :

Modulating signal Frequency :

Carrier signal amplitude :

Carrier signal Frequency :

Modulated signal Frequency :


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AMPLITUDE MODULATION

Aim: To construct an amplitude modulator and observe the wave forms.

Components required:

1. IC trainer kit 2. Function generator 3. Transistor 4. IFT 5. Capacitors and resistors as shown in the circuit diagram. 6. Transistor, BC-107

Theory:

Modulation is the process of characteristics of a high frequency sine wave is varied in accordance with

the instantaneous value of the modulating signal. In amplitude modulation, the amplitude of a carrier signal is

varied in proportional to the instantaneous amplitude of the modulating voltage, whose frequency is

invariably lower than that of the carrier. The carrier may be a high frequency signal while the modulating

signal is of low frequency. When a carrier is amplitude modulated, the instantaneous amplitude modulating

voltage variations are superimposed onto the carrier amplitude. Thus, when there is temporarily no

modulation, the amplitude of the carrier is equal to its UN modulated value. The bandwidth required for AM

is twice the frequency of the modulating signal. In modulation by several sine waves simultaneously, the

bandwidth required is twice the highest modulating frequency.

In the circuit shown, modulating signal is applied to the base of the transistor. Carrier frequency of 455

KHz is generated in the circuit itself by making use of IFT and associated component (Hartley oscillator) and

applied to the collector of the transistor. Modulated output is taken as shown.

The modulation index m=Vs/Vc, where Vs is the amplitude of modulating signal and Vc is the amplitude of the

carrier. The modulation index is a number lying between 0 & 1, and it is often expressed as a percentage. If

Vs>Vc, m will greater than one and distortion will occur.


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Procedure

The circuit should be connected first; only then the power supply should be switched on.

1. Measure the frequency & amplitude (p-p) of the fixed carrier signal present on the kit.

2. Connect the circuit as per the given circuit diagram.

3. Apply fixed frequency carrier signal to carrier input terminals.

4. Apply modulating signal from function generator of 1VP-P of 500Hz.

5. Note down and trace the modulated signal envelop on the CRO screen.

Result

Observed the modulating signal, carrier signal and modulated signal on CRO

Plotted these waveforms on a graph sheet.


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AM DETECTOR

Observations Vmax of the input modulated signal = Vmin of the input modulated signal = Amplitude of the detected signal = Frequency of the detected signal =


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AM DETECTOR

AIM:-

Construct an AM detector (demodulator) and observe the waveforms.

COMPONENTS AND QUIPMENTS REQUIRED:-

AM modulator

Diode - OA 79

Capacitors - 0.01 µF (2 Numbers), 0.1 µF (1 number)

CRO - 1 No

Resistor - 470 ohm (1 number)

PRINCIPLE:-

The reverse process of modulation is called demodulation or detection.

Demodulation is the process of recovering modulating wave from the modulated wave.

Semiconductor diodes are the most common device used for demodulation for AM signals.

During the positive half cycles of the modulated wave, the diode conducts while during negative half

cycles, it does not. The result of this rectifying action is that out put of the diode consists of positive

half cycles of modulated wave. The rectified modulated wave contains radio frequency and the signal.

The RF component is filtered by the capacitor C of 0.01 µF. The value of this capacitor is sufficiently

large to present low reactance to RF component while presenting a relatively high reactance to the

audio signal. The two capacitors of 0.01 µF and 470 ohms form the π filter. The result is that the RF

component is bypassed by the two grounded capacitors and thus we obtain the audio signal only. If

we sketch the waveform before 0.1 µF, it will be a positively clamped one and after o.1 µF capacitor,

waveform will be a pure ac.


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PROCEDURE

1. Make the connections as shown in the circuit diagram.

2. For demodulator, the modulator output is fed to the circuit.

3. Observe the input and output on CRO.

4. Measure the voltage and frequency of the detected waveform.

5. Plot these waveforms on a graph sheet.

RESULT Constructed the AM detector and observed the output on CRO.


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FM MODULATION

1 V-

2 INPUT

3 INPUT

4 VCO OUTPUT

5 Phase Comparator input

6 REF output 7 VCO control voltage

8 EXT. Resistor

9 EXT. Capacitor

10 +V

11 NC

12 NC

13 NC 14 NC


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FREQUENCY MODULATION Aim: To set up a frequency modulator using IC LM 555

Components Required:

1. IC – LM555 - 1 number

2. Resistors – 4.7K, 10K, 33K - 1 each

3. Capacitors – 0.1 MF, 0.001 MF - 1 each

4. Dual power supply, +12 - 0 -12 - 1 number

Principle

Frequency modulation is defined as a system of modulation in which the frequency of the

carrier is made proportional to the instantaneous value of modulating signal. Amplitude of the

modulated wave remains constant at all times. The amount by which the carrier frequency is

varied from its UN modulated wave is called frequency deviation.

FM has many advantages over AM.

LM 565

LM 565 IC can be used for frequency modulation and demodulation purpose. It can be

used as voltage to frequency convertor. LM 565 contains a voltage controlled oscillator, a phase

detector and a voltage amplifier. The VCO section in this IC is used to create FM waveform. VCO

free running frequency can be adjusted with R1 and C1 connected to pins 8 and 9 respectively.

The input is applied through the capacitor C2, which acts as dc blocking capacitor and is

superimposed on the control voltage. This causes the dc control voltage at pin 7 of the VCO to rise

and fall with the input modulating signal. The modulating signal now has a dc level. Voltage

divider R2-R3 sets this dc level which controls the carrier frequency. As the dc voltage rises, VCO

frequency decreases in direct proportion to the


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amount of rise. The voltage rise is actually the same thing as the amplitude of modulation of the

information. Thus positive information causes negative carrier frequency change or deviation. The

opposite effect happens in the negative peak of the modulating signal. Thus frequency

modulation occurs.

The frequency produced by this IC, f=

Procedure

1. Rig up the circuit as shown in the figure

2. Provide a power supply of +10V and -10V

3. Do not apply any voltage at pin 7

4. Observe the output at pin 4 on CRO (square wave).

5. Now apply a modulating frequency of about 5 KHz as the input signal to pin 7 through a 0.1

MF capacitor

6. Note the modulated output.

7. Plot the waveforms on graph sheet.

Result

Studied the Frequency Modulator circuit.

Observed and plotted the waveforms on graph sheet.

Observations

Modulating signal amplitude =

Carrier signal amplitude =

Modulating signal frequency =

Carrier signal frequency =


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FM DEMODULATOR

Centre frequency of VCO, fc = = 100KHz Let C1 = 0.001MF Then, R1 = 3 K (Use 10 K Pot)

Free running frequency of VCO = ………………Hz Amplitude of modulating signal = ……………..V Frequency of modulating signal = …………….V


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FM DEMODULATOR

Aim: To study about the FM demodulator circuit

Materials Required:

LM565 - 1 number

Resistors - 10 K Pot

Capacitors - 10 Mf, 0.1 MF, 0.001MF

Theory

The loop is set to run at 100KHz by C1 and R1. Potentiometer, R1 alows adjustment of the

free running frequency. The free running frequency should be same as that of the carrier

frequency of the modulator. FM signal is coupled to pin 2 ( Phase detector input) through C2. The

VCO control voltage of the loop on pin 7 of 565 contains two components. One is a dc level

corresponding to the average frequency going into the PLL from the FM modulator and the other

is an ac level that is actually the detected information signal. This ac signal arises because of the

PLL’s self correcting action; as the transmitter deviates up or down in frequency, the PLL attempts

to force the VCO to follow this frequency exactly by varying its control voltage. Thus the control

voltage is a copy of the original information signal. A capacitor C3 us connected between pins 7

and 8 to avoid oscillation in the control current source. Capacitor C4 forms a low pass filter along

with the internal resistor, 3.6 K when connected between pin 7 and positivel supply line.

Procedure

1. Set up the circuit

2. Use power supply of +10 V.

3. Do not apply FM input first.

4. Observe the output at pin 4 on CRO. (VCO output is a square wave)

5. Adjust the potentiometer, R1 so that the free running frequency of VCO at pin 4 is 100 KHz.


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6. Now apply FM input.

7. Observe the output at pin 7. Note While doing the experiment, increase the deviation of FM wave at the modulator circuit by

adjusting the amplitude of the function generator. As the deviation increases, you can observe

that the demodulated output begins to become distorted.

Result

Studied about frequency demodulation.

Free running frequency of VCO =

Modulating signal amplitude =

Modulating signal frequency =


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LAY OUT OF RADIO PCB (Square Board)


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SAMPLE LAY OUT OF RADIO PCB

Aim:

1. To know the component layout of radio receiver PCB.

2. To sketch the lay out

3. To identify stages of radio receiver.

4. To identify and familiarize various components on PCB.

Requirements

Radio receiver, Screw driver set

Theory:

Lay out is the component side view of the PCB, arranged in a systematic order. The lay out designing is in

such a way as to reduce circuit complexity and the various stages of the radio receiver circuit. If we get

familiarized with the lay out, stage and appropriate component identification will become very easy.

Procedure

1. Collect radio receiver and tools.

2. Open the back cover of the radio receiver with screw driver.

3. Observe the wiring and locations of various components.

4. Carefully take out the PCB from cabinet.

5. Identify various stages and components of receiver PCB.

6. Replace the back cover and tight it.

Result.

1. Understood the component layout of radio receiver PCB (square board) and sketched it.

2. Identified various stages in the radio receiver.

3. Identified the components soldered/fitted on PCB.


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SUPER HETERODYNE RADIO RECEIVER

Block Diagram and Working


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SUPER HETERODYNE RADIO RECEIVER

Aim: To study about the block diagram of a super heterodyne radio receiver and its working.

Working Antenna coil selects the radio wave of one radio station from many radio waves striking the antenna of the receiver. Each transistor radio has at least one antenna coil. Gang capacitor is connected in parallel to it for the purpose of tuning. Volts Developed In Secondary Of Antenna Coil. By transformer action, volts of selected RF carrier signal developed on the secondary of the antenna coil. Audio signal remain amplitude modulated on these carrier signal in the same way as were sent by the radio station. Converter Section Converts the incoming signal received by the antenna to intermediate frequency of 455 KHz. Advantages of a converter section In the absents of converter circuit, high frequency amplifier circuit of a radio will have to amplify all the frequencies lying between 545 KHz and 23 MHz Uniform amplification of all these frequencies is not possible with one circuit. Several circuits are required to amplify different range of frequencies. Intermediate frequency, IF – 455 KHz. IF Amplifier Amplify several hundred times the 455 KHz signal coming out of converter section. Amplified signals are given to detector section. Detector and Filter Section From the amplified IF signal, this circuit separates audio signal and ground IF carrier signal. Separated audio signal are of very low volts. These low volt signals are sent to audio amplifier for amplification. Audio Amplifier Circuit Audio signal coming out of detector section are amplified several hundred times by this circuit and is given to loud speaker. Loud Speaker Coverts amplified audio signal to sound waves. Result Studied the block diagram of radio receiver


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CONVERTER SECTION

Biasing voltages of BF 194 B

Emitter - ____V

Base - ____V

Collector - ____V

Coil Resistances

Particulars

Primary Secondary

M.W Antenna coil

M.W Oscillator coil


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CONVERTER SECTION

Aim:

To set up the circuit of a converter section on a square board.

Theory Converter section consists of an oscillator coil, a mixer transistor, IFT, antenna coil, Gang and trimmer capacitors. When dc supply is given to transistor radio, its oscillator starts working. The frequency of oscillations can be changed by rotating the variable capacitor attached to the oscillator coil. The frequency of oscillator is always 455 KHz more than the carrier frequency selected by antenna coil. Oscillator signal is sent to emitter of mixer transistor. The antenna coil signals are sent to the base of mixer transistor. Transistor mixes these two signals and generates a new carrier frequency. The frequency is equal to the difference of the two frequencies. i.e., 455 KHz and audio signal remains amplitude modulated as before. 455 KHz signal are selected and amplified by the IF amplifier section. Transistor BF194B act as the mixer in the converter section. Dc supply is given to its base through 390 ohms resistor. DC supply is given to the collector through a resistance of 470 ohms, primary coil of IF transformer, primary of oscillator coil and 100 ohms resistance. Its emitter is grounded through a resistance of 1.5K. As transistor gets proper volts, current starts flowing in it. As the current increases in the primary of oscillator coil, some electrical energy reaches in the secondary coil. Because of the gang capacitor connected in parallel to the secondary coil, oscillations starts. These oscillations are given to the emitter of transistor through .01micro farad capacitor. Signal selected by antenna coil are given to the base of transistor through .01microfarad capacitor. This capacitor does not allow dc to reach to antenna coil. IFT is tuned to 455 KHz by connecting a 2700 PF capacitor in parallel to it and by rotating the core of IF transformer. Signals of the other frequencies are grounded. Antenna coil, oscillator coil, gang and trimmer capacitors are generally kept outside the PCB. These are connected to PCB with wires. Procedure:

Check the components, Measure and note down the resistance of all the coils used. Solder the

components on the square board given, Fix the gang capacitor and ferrite rod in their respective places.

Measure the biasing voltages at emitter, base and collector of the convertor transistor, BF 194B and note

it down

Result:

Studied the converter section of the radio receiver on square board


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USE AND CONNECTIONS OF A BAND SWITCH


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USE AND CONNECTIONS OF A BAND SWITCH

Aim:

To connect band switch to the circuit

Theory

In a transistor of 1 band, antenna and oscillator coils are permanently connected to aerial, gang capacitor

and with the base, emitter and collector of the mixer transistor. But if the transistor radio is more than

one band, then permanent connections are not possible. The oscillator and antenna coils of one band

only should get connected to mixer transistor, gang and aerial at one time. Rest of the coils should remain

cut from the circuit.

The following 4 connections are required to be changed to switch from one band to another band.

P1 Antenna Gang with Primary of Antenna coil

P2 Base of convertor with Secondary of Antenna Coil

P3 Oscillator gang with Secondary of Oscillator coil

P4 Emitter of convertor with Secondary of Oscillator coil

All these four connections can be changed simultaneously with the help of a band switch and the coils of

any one band can be brought in circuit.

Procedure

1. Check the band switch connections by using a multimeter in resistance range.

2. Connect the band switch as shown in the circuit.

Note

Special care should be taken while connecting the band switch to the circuit as there are many chances of

mistakes

Result:

Studied about the band switch and connected the switch to the circuit.


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IF SECTION AND DETECTOR SECTION

Measurement of coil resistances of IF Transformers

First IFT (Yellow)

Primary resistance = _______Ω

Secondary resistance = _______ Ω

Second IFT (Green)



Third IFT (White)




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IF SECTION AND DETECTOR SECTION

Aim: To set up the circuit of an IF amplifier and a detector stage on a square board.

Theory

Two transistors and 3 three IF transformers are used in IF Section. First IFT is the oscillator IFT, 2nd

one is the Inter IFT and the last one is the detector IFT. The primary of first IFT is attached to the collector

of mixer transistor BF 194 B. Very low volt IF signals develop at the secondary which are given to the

base of first IF transistor BF 195C. This transistor amplifies IF signals. Amplified IF signals are available at

the collector and develop in the primary of second IF transformer. From here, they reach the secondary

and the base of second IF transistor BF 195D. The transistor further amplifies the signals. There signals

become available at the collector and develop in the primary coil of 3rd IF transformer. By transformer

action, they reach the secondary coil and from here given to detector section.

Detector Section

Detector section consists of a diode, a high frequency filter and a variable resistance known as

volume control.

Due to the presence of diode, only negative half cycles of 455KHZ amplitude modulated signals produces

current in detector section. The two capacitors used in pie filter are of low capacity and only allow high

frequency IF signals to reach ground.

Low frequency audio signals develop their volts in the variable resistance known as volume

control. By rotating the shaft, the value of audio signals available at the middle terminal can be increased

or decreased. From the middle terminal of volume control, audio signals are sent to the audio section &

then to the load speaker.

AGC (Automatic Gain Control) (AVC)

The function of this section is to produce sound of approximately same intensity in loud speaker,

whether the signal developed in the antenna coil is of low volt or high volt. It can be achieved if the IF

transistor BF 195C amplifiers more when their volts are low and amplifies less when their volts are high.

For such amplification, a negative DC voltage of changing value is obtained from the detected audio

signals and is mixed with the base supply of the transistor BF 195C. The value of negative DC voltage

depends on the value of audio signals. When audio signals of higher voltage come, more negative DC

voltage is produced. It is obtained from AGC generator circuit made of resistor and electrolytic capacitor.

This AGC supply is given to the base transistor BF 195C through the secondary of first IF transformer.


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Biasing Voltages

BF195C

Emitter -

Base -

Collector -

BF195D

Emitter -

Base -

Collector -


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When more audio comes, more negative AGC is formed which decreases base volts of transistor BF 195C.

Transistor amplifies less in this condition. When less audio comes, less negative AGC is formed. It

increases base volts and the transistor amplifies signals more.

Circuit Diagram

BF 195C acts as first IF amplifier. IF signals are given to its base from the secondary of first IFT

connected to the collector of mixer transistor BF 194B. DC supply through 220K resister and AGC supply

are also given to the same base. Its collector gets DC supply through 470Ω resistor and primary of IInd

IFT. IF signals developed at the secondary are given to the base of BF 195D. DC supply is given to its base

through 180K Ω. DC supply is given to its collector through 220 Ω resistor and primary of 3rd IF

transformer. Amplitude modulated amplified 455KHZ IF signals develop in the secondary of 3rd IFT.

OA79 rectifies IF signals. 470 Ω resistor and the two 0.01 MF capacitors form a pie filter and send IF

carrier signals to ground. Audio signals develop at 10K volume control. From the middle terminal of

volume control, audio signals are sent to audio amplifier circuit.

Procedure

1. Check all the components before connecting in the circuit. 2. Note down the resistances of primary and secondary coils of all the IFTs. 3. Verify whether a capacitor is present in each IFT. 4. Rig up the circuit. 5. Avoid dry soldering and short circuit in the PCB 6. Measure the voltages at different terminals of transistors and mark it. 7. Mark the forward and reverse resistances of the diode, OA79.

Result

Constructed the circuits of IF stage and detector stage on a square board.

Measured and marked the coil resistances of each IFT and biasing voltages of BF195C and BF195D.


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Audio Driver Transformer

Resistance of the primary winding (between terminals 1 & 2) = ________Ω

Resistance of the secondary winding (between terminals 3&4) =________Ω

Resistance of the secondary winding (between terminals 5&6) =________Ω

Biasing Voltages

BC 148A

Emitter = ________V

Base =________V

Collector =________V

BC 148B

Emitter = ________V

Base =________V



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AUDIO SECTION OF RADIO RECEIVER

Aim:

To set up both audio voltage amplifier and power amplifier circuits on a square board.

Theory

Generally 2 NPN and 2 PNP transistors are used in audio section of a transistor radio. PNP type transistors

are used in a push pull circuit.

From the middle terminal of volume control, audio signals are sent to the base of transistor, BC 148A.

Amplified signals appear at the collector and are then sent to the base of transistor BC148B. It amplifies

them further. And the amplified signals develop in the primary coil of driver transformer attached to the

collector.

Driver transformer has 2 secondary coils of equal number of turns. By transformer action, similar audio

signals develop in the 2 secondary coils. In the circuit, when terminals 3 and 5 becomes positive,

terminals 4 and 6 becomes negative, hence signals developed at terminals 3 and 6 are opposite volts.

Signals of opposite volts developed at terminals 3 and 6 are given to the bases of the two PNP transistors

AC 128 and AC 128 joined in series.

Even in the absence of audio signals, current flows in the two AC128 transistors, and 6V dc supply

becomes divided equally on them. 3 V develop at the junction of 2 transistors. One end of the loud

speaker is attached to this junction and the other end is attached to another supply also of 3 V. No

current flows through the loud speaker as equal volts are present at its two ends.

When audio signals reach the terminals 3 and 6, base volts of one PNP transistor increase and of the

other decrease. Which ever transistor has its base voltage equal or more than the emitter volts, current

stops flowing in that transistor. The other transistor’s current now flows through the loud speaker and

the 3 V battery.

So, for half cycle of audio signal, if current flows through the transistor1 and the loud speaker; for the

other half cycle of audio signal, current flows through the transistor2 and the loud speaker. Hence one

transistor amplifies one half cycle of the audio. Such type of a circuit is known as PUSH PULL circuit.


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AC 128

Emitter = ________V

Base =________V


AC 128

Emitter = ________V

Base =________V


Voltage between loudspeaker terminals


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Circuit Diagram

From v/c, audio signals are given to the base of the transistor BC148A through a capacitor. Dc supply is

given to this base through a resistance of 1 MΩ. Amplified audio signals at the collector are given to the

base of BC148B through a capacitor. DC supply to this base is given

through a resistance of 220 KΩ. amplified audio signals develop at the collector and reach the bases of

transistors AC 128 and AC 128 through the driver transformer.

DC supply is given to these bases from a potential divider circuit formed from 47Ω, 820Ω, and 47Ω and

820Ω resistances. By push pull action, audio signals reach the loudspeaker which converts audio signals to

sound.

DC supply is given direct from the battery to BC 148B, AC128 and AC128. 150 ohm resistance decreases

the value of supply for other transistors of the radio. 100MFD capacitor attached to 150 ohm resistor

performs the work of de coupling. Any of the RF, IF or audio signals reaching the supply line are grounded

by the d coupling capacitor.

Procedure:

Check all the components using a multimeter. Measure the resistances of both primary and secondary

windings of the audio driver transformer. Connect the power ON/Off switch of volume control to the

board. Take voltages at different points in the circuit like speaker points, terminals of transistor etc and

mark them. Give any audio signal to the input of the circuit and see whether loud speaker gives full audio

sound. Then we can conclude that audio stage is working perfectly.

Result:

Assembled the audio stage of a radio receiver on the square board and tested its performance.

Measured biasing voltages of the transistor and the resistance of both primary and secondary coils of the

audio driver transformer and marked them.


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TESTING WITH SIGNAL GENERATOR

Aim:

To check whether different stages of radio receiver which you have assembled is working using Signal

Injection Technique.

Procedure

Sl. No Signal From

Generator

Reading Point Indication Result

1 AF Collector of AF Driver Whistling sound

from speaker

Audio Power amplifier

working

2 AF First lead of volume control

which is not grounded

Whistling sound

from speaker

The pre-amp driver and

power amplifier are

working

3 Modulated

IF

Base of the first IF

Amplifier

Whistling sound

from speaker

The IF amplifier and

subsequent stages are

working

4 Modulated

IF

Base of Converter Whistling sound

from speaker

AF, IF and Mixer Stages are

working

Result

Checked different stages of Radio Receiver


41

IF Alignment Aim: To study about the IF alignment To carry out alignment of IF stage in the radio you have assembled. Equipments Required: Signal Injector, Screw driver, Multimeter Procedure:

1. Make sure that the IF offset which is to be aligned is generally 455 KHz

2. Set the volume control to maximum

3. Put the receiver into medium wave band and set the gang to get maximum capacitance.

4. Connect the multimeter at ac range of 50V across the output of audio power amplifier.

5. Set the signal generator at IF (455 KHz).

6. Connect the positive lead of the signal generator to the base of BF 195D with a 0.01MF capacitor

connected in series with the positive lead.

7. Connect the earth lead of signal generator to the chassis of the set.

8. Now adjust the trimmer of last IF transformer (white). Note the multimeter reading. Adjust it for

the maximum reading on the multimeter. It can also be adjusted by connecting a loud speaker at

the output of AF amplifier. In that case, it is tuned for maximum sound. If the sound is too loud,

adjust the attenuator of the Signal Generator.

9. Now connect the positive lead of signal generator to the base of the inter IF amplifier, BF 195C

without disturbing the frequency of the signal generator.

10. Adjust the tuner IFT for maximum response in the loud speaker or maximum reading of

multimeter. If response is too loud, adjust the attenuator of signal generator.

11. Now connect the positive lead of signal generator to the base of BF 194B without disturbing the

frequency of signal generator

12. Adjust the IFT for maximum response as above.

13. Repeat the three adjustments once again in the sequence and the IF is ready for working

Result

Studied about IF alignment procedure.

If alignment is carried out satisfactorily as per the given directions.


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RF ALIGNMENT Aim:

To study about RF alignment

Materials Required

Soldering Iron

Tweezer

Screw driver

Medium wave antenna and oscillator coil

Short wave antenna and oscillator coil

Signal generator

Multimeter

Procedure

Connect the negative e lead of signal generator at the chassis of the receiver and positive

lead at the antenna input

Connect a multimeter on ac range across the secondary of the sound transformer. A speaker can

also be connected

The modulated signal is fed from the signal generator to the given points

Circuit Signal

generator

setting

Signal

generator

termination

Signal

generator

Connection

Receiver

strength

Adjustment

M.W 1560 KHz 233 KPF Aerial 1560 KHz Oscillator, Trimmer and antenna

S.W 1 2.5 MHz 233 KPF Aerial 2.5 MHz Oscillator, Trimmer and antenna

S.W 2 7.5 MHz 233 KPF Aerial 7.5 MHz Oscillator

S.W 3 22 MHz 233 KPF Aerial 22 MHz Oscillator

Result

Studied about RF alignment procedure

Carried out RF section alignment as per the given directions


43

TROUBLE SHOOTING CHART BASED ON SYMPTOMS IN A RADIO RECEIVER Aim: To study about different troubles and the defective stages connected with a super heterodyne receiver

Sl. No

Symptoms Defective Stages Probable Faults

1. Radio Not Working (Dead Receiver)

Power supply stage Short or open circuit in connecting wires, transformer or rectifier Defective rectifier or short filter capacitor

2 No output Speaker, Audio Stage

Short or open circuit in connecting wires of audio stage Defective speaker Defective transistor

3 Hum in sound Power supply Filter capacitor in power supply section is open

4 Less output Audio stage, IF stage

Defective transistors/ coupling capacitors/ resistors Less gain in IFT

5 Variation in output or noise

AGC Feed back resistor from detector to first IF stage damaged.

6 Motor boating sound from speaker

Detector Stage Open bypass capacitor for RF signals at detector stage

7 Continuous whistling sound

Mixer Stage Emitter coupling capacitor of mixer transistor became short

8 No medium wave RF stage Short/open circuit on antenna coil / oscillator coil or band switch wiring

9 No short wave RF stage Short/open circuit on antenna coil / oscillator coil or band switch wiring

10 No Medium Wave and short wave

RF, Mixer IF or detector stages

Short/open circuits in coils, gang or band switch Defective transistors in Mixer or IF stage Defective detector stage

Result Studied about different troubles and the defective stages connected with a super heterodyne receiver


44

TESTING OF RADIO PARTS USING MULTIMETER

PIN NO. RESISTANCE CONCLUSION

1 – 3 2 – 3

Very low ohm - Very low ohm -

Primary okay

4 – 5 Very low ohm - Secondary okay

3 – 5 1 – 4

No movement of needle No movement of needle

No short between primary and secondary

1 & metal container 5 & metal container

No movement of needle No movement of needle

No short between coils and container


45

TESTING OF RADIO PARTS USING MULTIMETER

Aim: To test different parts of Radio with Multimeter

Procedure

Resistance: Find the value of resistance from the meter and from the colour code. Change the resistance

if meter shows more than 5% difference.

Disc Capacitor: Value of these types of capacitors is generally printed on them or in terms of number

code. There should not be short or leakage in a capacitor. Use the multimeter in 1 MΩ range to test this

type of capacitor. If no movement of needle takes place, the capacitor is neither leaky nor short.

Electrolytic Capacitor: Use multimeter in 1MΩ range to test the capacitors. If the capacitor is good, the

needle should take a sudden jump in the beginning and should return slowly, and should stop at the mark

of 50KΩ or more. If the needle stops at low ohms, the capacitor is either leaky or short. If no movement

of the needle takes place by connecting in the same way after shorting its leads, diode will be open.

Gang Capacitor: Use multimeter in 1MΩ range. Connect the probes with the middle terminal and an end

terminal of the gang and rotate the shaft slowly. The movement of needle should take place if the

capacitor is good. Test the other part of the gang in the same way.

In most gang capacitors, the capacity increases when the shaft is rotated in anti-clockwise direction.

ON/OFF Switch and Volume Control

ON/OFF switch is present between the terminals marked as S-S and 1,2and 3(in figure) are the terminals

of the volume control.

Rotate the shaft to bring the switch at OFF and connect the probes with S and S. no current should pass

through the switch. i.e., no movement of the needle should take place. Now make the switch ON. The

current should pass through the switch; the needle of ohm meter should rotate, and reach 0 ohm mark. If

it does not happen, the switch is faulty.

Attach the probes of ohm meter at the terminals 1 and 3 of the volume control. The reading should be

equal to the value written on the volume control. Now connect the probes with terminals 1 and 2 and

rotate the shaft. On one direction of rotation, the reading should reduce to zero ohms and in the other

direction, the reading should increase towards the value written on the volume control. If it does not

happen, the volume control is faulty.

LOUD SPEAKER: Connect one probe of the ohm meter with one terminal of loud speaker. Connect and

disconnect the second probe of the meter with loud speaker again and again. The needle of the meter

should move and click sound should come from the speaker. If it does not happen, loud speaker is

defective.


46

IF TRANSFORMER:

Terminals 1, 2 and 3 belong to the primary coil and terminals 4 and 5 belong to secondary coil of IFT (in

figure). The two coils are kept insulated from each other as well as from the metallic container. IFT will

not work if any one of the coils breaks down, or if the two coils become short among themselves or with

the metal can. In 10K range, measure the resistance between the terminals of IFT as shown in figure.

If different comes in any one reading, the IFT is defective. If a capacitor is present inside the IFT, it should

also be alright

Driver Transformer

One primary coil and two secondary coils are generally present in a Driver Transformer. Neither of these

coils is open nor short among themselves or short with the metal container. This transformer is also

tested like an IF transformer. Small resistance should come between primary winding, first and second

secondary windings

Coils

An oscillator coil has 5 terminals for connections, whereas an antenna coil has 3 or 4 terminals for

connection. The terminals are attached to small metal parts having paints of different colours on them.

The colours are used to recognize different terminals of the coil.

Oscillator Coil

The terminals of primary coil have RED paint and WHITE paint applied on them. RED end is connected to

DC supply through IF transformer whereas the WHITE end brings DC supply to the collector of MIXER

transistor.

The terminals of secondary coil have GREEN, YELLOW and BLACK paints applied on them. Green end is

connected to oscillator GANG, Yellow end to emitter of converter transistor and Black end is connected to

Ground.


47

As an oscillator coil is really a transformer, it is also tested like an IF transformer. The primary and

secondary coils should neither be open nor short among themselves. Hence multimeter should show

some ohms between white and red, green and yellow and between green and black. The needle should

not move when the probes are attached to red and black.

Antenna Coil: The terminals of primary coil to be attached to antenna gang are painted green. The

terminal to be connected to the base of mixer transistor id painted blue. If the coil is of 3 terminals only,

then the third terminal is painted black. It is connected to ground either direct or through a loop aerial.

If the coil is of 4 terminals, then the third end is painted red and the fourth end is painted black. Red paint

is present on the other terminal of primary and is connected to ground either direct or through a loop

aerial. Black paint is present on the other end of secondary and this end is connected directly to ground.

The radio frequency spectrum is divided into major bands: Frequency: Wavelength (in meters): VLF very low frequency 3 KHz – 30 KHz 100 Km – 10 Km LF low frequency 30 KHz – 300 KHz 10 Km – 1 Km MF medium frequency 300 KHz – 3 MHz 1 Km – 100 m HF high frequency (a.k.a. short wave) 3 MHz – 30 MHz 100 m – 10 m VHF very high frequency 30 MHz – 300 MHz 10 m – 1 m UHF ultra high frequency 300 MHz – 3 GHz 1 m – 100 mm SHF super high frequency 3 GHz – 30 GHz 100 mm – 10 mm EHF extremely high frequency 30 GHz – 300 GHz 10 mm – 1 mm


48

FAULT ANALYSIS OF RADIO RECEIVER

The fault of a radio can be analyzed on the basis of sound it produces. The sound may be good or distorted or there may be no sound at all. Our first motto is to identify the section (block) which has gone faulty. This can be done by injecting a signal either by signal injector or by grounding the test point and by noticing the sound produced by the loud speaker. (Signal injection method). After identifying the section, follow voltage analysis technique to identify the faulty component. For this, biasing voltages of active components (eg. Transistors) if any in the particular section should be taken. From the biasing voltages taken, try to identify the faulty component, then replace it and make the radio receiver work. The faults connected with a radio receiver come under three heads.

1. No sound, No audio – Dead Receiver. (Audio refers to the hissing sound that occurs when there is no sound transmission).

2. Audio Okay, no sound 3. Distorted sound (eg. Motor boating sound).

In the first case, the fault will be with the power supply section or with the audio power amplifier section. 2nd case arises if there is some kind of faults with Mixer, Oscillator, IF section, Detector, AGC and voltage amplifier sections. Fault analyzing Procedure Symptom: Ex. No sound, Audio okay Possible faulty sections: 1. 2. 3. (If the student is very much familiar with the working of radio receiver, he / she can very easily chalk out the probable defective stages) Procedure 1. Tracing the faulty section by signal injection method

Action taken Observation

Ex. Signal injected at the base of voltage amp transistor

Tone heard from loud speaker

Signal injected at the cathode of OA79 sound heard from speaker

Signal injected at the input of 1st IF transistor No sound from speaker

Conclusion: Fault with IF section. 2. Voltage measurement method to find the faulty component in the section

Action taken Observation

1. Take the biasing voltage of BF 195C Emitter – Base - Collector

2. Take the biasing voltages of BF 195D Emitter – Base - Collector


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If the biasing voltages of transistors are not correct, analyze the problem so as to see what all components might have gone faulty and list out the possible faulty components. Now check each component separately. Replace the faulty component and see whether the set works properly Result Replaced the faulty component (Specify the component and its specification). Set working properly.

VARIOUS METER BANDS OF RADIO STATIONS Wave length of radio waves:- The length of a radio wave is known as its wave length. It is measured in meters. Frequency of radio waves:- All radio waves travel with a speed of 3×108 m/s in sky or in air. Relation between wave length, frequency and speed:- Wavelength × frequency = speed Wavelength × frequency = 3×108 m/s Wavelength and frequency of radio waves:- The wavelength of RF carrier radio waves generated at different radio stations lie between 13 meters and 550 meters. Frequency of 13 meter long wave = (3×108 m/s)/13 =23 MHz Frequency of 550 meter long wave = (3×108 m/s)/550 =545KHz Medium Wave Band (Mw) Radio waves having wave lengths between 200m and550m are known as the wave of medium wave band. These frequencies lie between 1500 KHz and 545 KHz. Short Wave Band: Radio waves having wave length between 13 meter and 120 meter are known as the waves of short band. Their frequencies lie in between 23MHz and 2.5MHz. Transistor Radios of 1 band, 2 band Medium wave band is present in all transistor radios; hence all radio receivers can receive programmes from 200 meters to 550 meters wave lengths. Transistor radios are made of 2 or more bands to receive programmes of Short wave band. If only one band of short wave is present, then the receiver can receive programmes between 19 meters and 60 meters. If 2 bands of Short Wave are present, then SW2 receives 16 meters to 41 meter programmes; and SW1 receives 41 meters to 90 meters programmes.


50

PA SYSTEM INSTALLATION


51

PA SYSTEM INSTALLATION

Aim: To Install the Public Address system and to operate its controls. Materials Required: Amplifiers, Loud speakers. Microphones Theory: The intensity of sound decreases with distance. Hence when a large gathering is to be addressed, sound needs to be amplified so that people at a distance from the stage may receive good intensity of sound. The system which fulfils this function is called Public Address System (PA system). PA system is an electro acoustic system in which sound is first converted into electric signal by microphones. The electrical audio signals are amplified, processed and fed to another transducer (loud speaker) which converts the audio signals into sound wave. Microphone: It converts sound signals into electric signals. Generally, amplifiers have option of two or more microphones in addition to an auxiliary input for tape recorder/CD player. Mixer: The outputs of microphones are fed to mixer stage. The function of mixer stage is to effectively isolate different channels from each other before feeding it to main amplifier. It can be either a built – in unit or a separate pluggable unit. There are commonly 3 types of mixers:-

1. That does not use Pre-Amps/Amps but uses only gain controls (faders) and isolating resistors 2. That uses a common pre – amp after isolating resistors (fig). P1 to P5 are isolating resistors and R1

to R5 are isolating resistors 3. That uses separate pre-amps for each channel and then after the gain control potentiometers and

isolated resistors. There will be a common amplifier and an emitter follower.

Voltage Amplifier: It amplifies the signals coming out of the mixer Process Circuit: These circuits have Master Gain Controls and tone-control circuits (Bass/Treble controls). These circuits are usually used to correct or control elements of sound. Procedure:

1. Collect the equipments and identify each connector. 2. Connect the given microphone and loud speaker to the PA and with suitable position. 3. Switch ON the PA amplifier and microphone. 4. Adjust the volume control of each microphone. 5. Adjust the overall volume level with master control. 6. Adjust the tone quality by using bass and trouble controls. 7. Check the sound volume and quality with different inputs.

Result: Installed the PA system and operated its controls.


52

DIRECT TO HOME (DTH)


53

DIRECT TO HOME (DTH) SYSTEM

Aim: To set up a DTH system

Theory:

Band Frequency

L 1 – 1.5

C 3.4 - 7

Ku 12 - 14

The Direct To Home (DTH) Television system enables viewers to receive many channels of high

quality TV Programmes via high power Ku band satellite

A DTH network consists of a broadcasting centre, satellites, encoders, multiplexers, modulators and DTH

receivers. DTH is an encrypted transmission that travels to the consumer directly through a satellite. DTH

transmission is received directly by the consumer at his end through the small dish antenna. A set-top

box, unlike the regular cable connection, decodes the encrypted transmission.

The provider selects programmes and broadcast them to subscribers as a set of package. The providers’ broadcast is completely digital which means it has much better sound and picture quality. The encoder converts the audio, video and data signals into the digital format and the multiplexer mixes these signals. At the user end, there will be a small dish antenna and set-top boxes to decode and view numerous channels. On the user's end, receiving dishes can be as small as 45 cm in diameter.

For multiple connections in the same premises, one can use the same connection. However, every television set will need to have an individual STB.

There are 5 major components involved with a DTH system. They are,

1. Programming source

2. The broadcast centre

3. The Satellite

4. Satellite Dish

5. The Receiver.

Programming sources are simply the channels that provide programming for broadcast. The provider doesn't create original programming itself; it pays other companies (HBO, for example, or ESPN) for the right to broadcast their content via satellite. In this way, the provider is kind of like a broker between you and the actual programming sources. (Cable TV companies work on the same principle.)


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Procedure

1. Select a suitable location for the Antenna

2. Fix the antenna loosely on the stand provided for it.

3. Fix the stand without jerking.

4. Never tighten the screws before tracking.

5. Connect one end of the cable to the LNB and the other end to the receiver input.

6. Connect the output of the receiver to the TV receiver either using RF chord or AV chord.

7. Make necessary adjustments so as the view the picture clearly.


55

The broadcast center is the central hub of the system. At the broadcast center, the TV provider receives signals from various programming sources and beams a broadcast signal to satellites in geosynchronous orbit.

The satellites receive the signals from the broadcast station and rebroadcast them to Earth. The viewer's dish picks up the signal from the satellite (or multiple satellites in the same part of the sky)

and passes it on to the receiver in the viewer's house. The receiver processes the signal and passes it on to a standard TV.

Encryption and Transmission After the video is compressed, the provider encrypts it to keep people from accessing it for free. Encryption scrambles the digital data in such a way that it can only be decrypted (converted back into usable data) if the receiver has the correct decryption algorithm and security keys.

Once the signal is compressed and encrypted, the broadcast center beams it directly to one of its satellites. The satellite picks up the signal with an onboard dish, amplifies the signal and uses another dish to beam the signal back to Earth, where viewers can pick it up.

Satellite Dish

When the signal reaches the viewer's house, it is captured by the satellite dish. A satellite dish is just a special kind of antenna designed to focus on a specific broadcast source. The standard dish consists of a parabolic (bowl-shaped) surface and a central feed horn. To transmit a signal, a controller sends it through the horn, and the dish focuses the signal into a relatively narrow beam.

The dish on the receiving end can't transmit information; it can only receive it. The receiving dish works in the exact opposite way of the transmitter. When a beam hits the curved dish, the parabola shape reflects the radio signal inward onto a particular point, just like a concave mirror focuses light onto a particular point. In some systems, the dish needs to pick up signals from two or more satellites at the same time. The satellites may be close enough together that a regular dish with a single horn can pick up signals from both. This compromises quality somewhat, because the dish isn't aimed directly at one or more of the satellites. A new dish design uses two or more horns to pick up different satellite signals. As the beams from different satellites hit the curved dish, they reflect at different angles so that one beam hits one of the horns and another beam hits a different horn.

The central element in the feed horn is the low noise block down converter, or LNB. The LNB amplifies the radio signal bouncing off the dish and filters out the noise (radio signals not carrying programming). The LNB passes the amplified, filtered signal to the satellite receiver inside the viewer's house.

Result

Set up a DTH system.

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TAPE RECORDER


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TAPE RECORDER

Aim: To study about the tape recorder, its mechanism etc.

Theory

Tape recorder is used for recording and reproduction of sound. It is a combination of mechanical

assembly and electrical/electronics units. Function of tape transport mechanism is to roll the tape

from one side to other side of the cassette and vice versa as and when required, ensuring

constant and swift speed of the tape. The tape mechanism also enables the tape to be wound

quickly on either side reel for fast forward and rewind operations. Tape transport mechanism

consists of the following components.

1. Motor: DC motor, generally in built in the circuit for constant speed. Its speed is also

adjustable.

2. Capstan: It is an accurately machined spindle. The tape is passed against the capstan by means

of a rubber roller

3. Fly Wheel: It is a heavy wheel made of metal and is fitted to the capstan shaft. This damps

minor variations in the speed.

4. Gear wheel: There are different arrangement of gears to have required speed in the directions

of play back, rewind and fast forward.

5. Heads: 2 heads commonly. One head for recording and playback and the other head is for

erasing

6. Rubber belt: Motor rotations are transferred to the capstan and fly wheel with the help of a

motor belt.

7. Spools: There are two spools. One spool feeds tape to the other spool. The spool that supplies

tape is known as supply spool and the one that receives tape is the take up spool.

You can record anything you want instantly and the tape will remember what you recorded for playback at any time.

You can erase the tape and record something else on it any time you like.

The Mechanical System

Tape Path

Tape starts from the SUPPLY REEL, runs past one or two TAPE GUIDES or TENSION ARMS, past the

ERASE, RECORD, and PLAY HEADS, between a CAPSTAN and PINCH ROLLER, past more guides and arms,

and finally onto the TAKEUP REEL.

Motion of the tape is controlled by the capstan. This is a steel shaft which is always turning at a constant

speed. When the PLAY button is pushed, the rubber pinch roller squeezes the tape against the capstan

and the tape is pulled past the heads. The TAKEUP MOTOR winds the tape onto the take up reel as this

goes on. Some back tension is necessary to keep the tape tight against the heads. This is generally applied

by providing a little power to the SUPPLY MOTOR (Which always runs backwards; it may also be called

the rewind motor.), although there are other methods.


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When the tape is to be rewound, the pinch roller stays away from the tape and full power is applied to

the supply motor making the tape zip backwards. (A low power is applied to the take up motor to keep

the tape tight.) To save wear and tear on the heads and to suppress some loud annoying sounds, one or

two TAPE LIFTERS pop up to pull the tape away from the heads during this operation. When the machine

is in the FAST FORWARD mode, the same sort of things go on, but this time the take up motor gets full

power.

There are brakes on both reel motors to stop the tape quickly and gently. Because the tape and reels can

build up a fair amount of momentum, care must be taken in going from one of the fast modes to the play

mode to avoid damaging the tape.

Result

Studied about the tape recorder and its mechanism.


60

CONTROLS OF A TAPE RECORDER

Aim:

To familiarize with the controls of a tape recorder and the way of operating them.

Theory

Play Button: On pressing this button, the tape mechanism gets power supply through a leaf switch

activated by the PLAY button. The Record/Play back head comes in contact with the tape and the pinch

roller engages the tape on the capstan. The capstan starts rotating due to the motor and Pinch Roller

rotates because of the friction between the capstan and pinch roller, the tape which is held between the

pinch roller and capstan is pulled by the rotational action at a constant speed.

Fast Forward Button

By pressing this button, the leaf switch closes, applying the supply to the motor. In this mode, the play

head does not touch the tape. The pinch roller does not make contact with the capstan. The take up

wheel rotates faster and the tape is pulled directly from the supply wheel and gets wound on the take up

wheel without going through capstan and pinch roller.

Rewind Button

By pressing this button, the leaf switch gets closed applying DC supply to the motor. The play head does

not touch the tape. The pinch roller does not make contact with the capstan. The supply wheel rotates

fast rolling the tape in the reverse direction of play.

Record Button

In some mechanisms, record button is interlocked with the play button in such a way when record button

is pressed, the play button is automatically depressed. In cheap mechanisms, both the play and record

buttons are to be pressed for recording. When a record button is pressed, the leaf switch gets closed,

applying DC supply to the motor. The erased head (permanent magnet type) is pushed forward making it

touch the tape thus erasing the existing information on the tape. The Play/Record head also touches the

tape, but now instead of reading information, the information to be recorded is transferred on the tape

through the head.

Stop Button

This button is used to release the mechanism from other modes such as Play, Record, FF and Rewind. This

button releases the leaf switch and cut off the supply to the motor.


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Eject Button

This button is used to take out the cassette from the tape recorder. Before pressing this button, the stop

button should be pressed. In modern mechanisms, the stop and eject buttons are provided in the same

switch so that a mailed press stops the tape function and the hard press eject the tape. Pressing this

button ejects the cassette compartment so that the cassette can be easily taken out of the compartment.

Pause Button

This button is used only during Play or Recording mode. On pressing this button, whether it is in play or

record mode, the tape movement is paused, but the dc supply to the motor is not cut off. On pressing

pause, the pinch roller is pulled back from touching the capstan, and the drive to the take up is

disengaged. This stops the pulling of the tape and the tape remains stand still. In this mode, the motor

will continue to run and recording/playback can be continued instantly. In regular record/play mode, the

motor takes sometimes to attain the required speed.

Result

Studied about the different controls of a tape recorder and the way of operating them.


62

HEAD CLEANING OF TAPE RECORDER


63

Head Cleaning of Tape Recorder

Aim: To clean the heads of a Tape Recorder Materials Required: Cotton swab(s), Rubbing alcohol, Small receptacle to hold alcohol, Tweezers, strong working light Theory It is a requirement when using a reel to reel tape recorder, that the heads and guides must be kept clean.

This should be done daily, especially if you are playing back recordings made on tape more than 10 years

old. Old tape often becomes sticky, shedding oxide at an alarming rate and this sticking soon causes loss

of quality, screeching and even slowing down if not attended to.

Procedure:

First equip yourself with some isopropyl alcohol or alternatively methylated spirit can be used, but does

not evaporate so quickly. You will also need some strong cotton buds

Disconnect the machine from mains electricity and set it flat on a table so that you can see the tape path

easily. Remove the head cover of the machine. This is usually achieved by evenly pulling the cover

upwards, but sometimes there are a couple of screws to be undone first. Some machines have two covers

to give excellent access to the heads and guides. Be careful on older machines as plastic parts often

become brittle with age.

Identify all the parts in the tape path. That is every part that the tape touches on its path through the

machine. All these parts will need to be cleaned thoroughly with the cotton bud soaked in the isopropyl

alcohol. Never use any metallic tools anywhere near the tape path. Pay attention to the guides where the

tape touches first on its journey from the supply spool. One of these may be a swinging pin and possibly a

rotating guide. Be sure to remove every trace of contamination from these as a lot of oxide may be

deposited on them. Pay particular attention to the upper and lower surfaces of the guides. Next to be

cleaned will be the erase head. If this is not particularly clean the erase performance of the machine will

be less than perfect.

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The next head will be the record head which must be clean to ensure full fidelity recording. If the cotton bud you are using has got dirty by now, change to a new one. Next head is the play head. This is most critical for accurate playing of recordings. Don't be afraid to be quite vigorous when applying the cotton bud, as it is essential to remove all traces of dirt. This is where the magnifying glass, mirror and strong light will come in handy. Keep cleaning in an up and down and side to side motion until the cotton bud comes away clean. Some cheaper recorders have a combined record and replay head. The advantage of having three heads is that you can listen to what you have recorded a fraction of a second later, confirming that no quality has been lost.

There may be other fixed or rotating guides depending on the type of machine. Just make sure they are all spotlessly clean and free to rotate. Don't disturb the adjustments on any of the heads or guides as this is beyond the scope of home maintenance. The next important parts for cleaning are the capstan shaft and the pinch roller. The capstan is a motor driven metal shaft which drives the tape through the machine at a constant speed by means of the rubber pinch roller which presses up to grip the tape and so pull it past the heads. The pinch roller may be very dirty on a neglected machine, so be sure to work your way all around it to remove all traces of residue. Rotate it by hand to achieve this. In extremely dirty cases it might be better to use a lint free cloth instead of a cotton bud as there may be too much dirt to be removed.

Lastly, there may be a further guide and possibly a swinging or fixed pin to attend to. These stabilize the tape before it passes to the take up reel and must also be very clean. Finally, replace the head cover and reconnect the power to your tape recorder. You will probably find that the quality of your machine has been restored. If the quality starts to be impaired again, especially when using old tapes, you will have to consider restoring your tapes and copying them to CD or some other modern format for the future.

Result

Cleaned the heads and other parts in the tape transport mechanism


66

HEAD REPLACEMENT OF TAPE RECORDER


67

HEAD REPLACEMENT OF TAPE RECORDER

AIM:-

a) To remove, test and replace play back/record head. b) To remove, test and replace erase head.

THEORY:-Generally tape recorders have two heads. One for play back and recording and the other one for erase

the record information on the tape.

Erasing head come to action only at the time of recording. There are three types of erasing – AC erasing, Dc

erasing and permanent magnet erasing. In the case of permanent magnet erasing, the erase head comes down

and touches the tape during recording. In the case of AC or Dc erase, one or two wire connections will be

available on erase head.

PROCEDURE:-

1. Remove the cassette door assembly of the tape recorder.

2. Locate the record/ play back head and record the printed data on the head.

3. Observe the soldered wires at the head and make a rough sketch of it along with wire colors.

4. De solder the insulated wires and shield wire soldered at the R/P head.

5. Loose the screws fitted at the left and right of the plate on which the R/P head is situated. Loose both screws

simultaneously and take out the screws, R/P head and a tension spring found below one of the screw (azimuth

adjustment).

6. Use a sharp tip (pencil tip) soldering iron, remove the excess solders. (NB: Do not hold the heated bit for a

long time at the terminal while cleaning as this may damage the coils inside the R/P head.

7. Clean the face of the R/P head using a cotton band dipped in pure alcohol or head cleaning solution. Check if

the R/P head face is free from dirt, dust, grease etc.

8. From the lookup of the head face, identify whether the head is a stereo or mono head.

9. Measure and record the resistance of R/P head using an ohm meter.

10. Fit the new R/P head in the tape recorder. While fixing the screws, first fix the screw with the spring and then

the other screw. Tighten the screw simultaneously.

TO REMOVE AND REPLACE ERASE HEAD

1. Locate the erase head. Identify and record the type of erase head.

2. Make a rough sketch of the wire connections at the rear of erase head. (in the case of DC and AC erase only)

3. Remove the screw for fixing the erase head and take out the erase head gently.

4. Clean the solder terminals (if any) on the erase head using soldering iron. Clean the face of the erase head

using cleaning solution and cleaning buds.

5. Measure and record the coil resistance of erase head (skip this step if the erase head is permanent magnet

type).

6. Now clean the new erase head. Measure and record its resistance.

7. While fixing the screws, tighten them simultaneously.

Result

Removed, tested and replaced Record/Playback head.

Removed, tested and replaced Erase Head


68

REMOVE AND FIX LEAF SWITCH OF TAPE RECORDER


69

HEAD ADJUSTMENT (AZIMUTH ADJUSTMENT)

AIM:-

a) To know the idea of head adjustment

b) To identify the head adjustment points

c) To perform the head adjustment

d) To verify the effect of head adjustment

THEORY: The misalignment of head has the effect of increasing the effective gap of the play back head.

This causes reduction in output at high frequencies. The recording/playback heads are mounted in a way

which permits alignment of the azimuth. The azimuth of the head can be adjusted by trimming the

azimuth adjustment screw. The head can be aligned with a special cassette test tape. These test tapes are

precision recorded on cassette tape recorders, the heads of which are aligned very accurately. The

frequency recorded on these cassettes for aligning head is about 4 KHz.

Equipment/Tools: Tape recorder, screw driver, cassette, multimeter

PROCEDURE:-

1. Place the cassette tape on the recorder

2. Connect the multimeter on a range 2.5V ac

3. Set the volume control to mid way

4. Play back the head alignment part of tape. If necessary, adjust the volume control for a

convenient reading on meter.

5. Adjust the head azimuth adjustment screw for maximum reading on the meter( by turning screw

slowly to one side and then to the other side till the output increases)

6. If head has been replaced, the azimuth may be much out. In this case azimuth should be adjusted

till a clear defined peak is obtained and the output reaches a maximum value.

Result: Head adjustment is done satisfactorily.


70

REMOVE AND FIX MAIN BELT OF A TAPE RECORDER


71

REMOVE AND FIX MAIN BELT OF A TAPE RECORDER

Aim: To remove and fix Main Belt of a Tape Recorder

PROCEDURE

1. Locate the motor in the tape recorder . Identify and record the specifications of motor.

2. Locate the flywheel. Rotate it with fingers and check if the flywheel 5rotate freely without any friction,

noise or sticky feelings. If any defects are noticed, record them.

3. Locate the idler wheel. Check whether it can be rotated without any friction. Record the defect if any.

4. Locate the main belt running around the motor pulley, idler wheel and fly wheel.

5. Rotate the idler wheel with your finger and check for any of the following belt defects.

a. Falling off from pulleys.

b. Slipping over the pulleys.

c. Not able to rotate the motor and idler pulleys.

d. Insufficient belt tension.

e. Twisted

6. Record defect if any

7. To remove the main belt from the assembly, loosen the flywheel cover plate screws by two or three

inches. Using a flat screw driver, slightly lift the cover plate upwards.

8. Slip the belt from the pulleys of the wheel and take out/pull it gently through the gap between the

flywheel and flywheel cover plate-belt removed.

9. Clean the new belt using paper to remove oil/grease deposits.

10. Insert the belt through the gap between the flywheel and the flywheel cover plate. Pass the belt over

the motor pulley and flywheel, then pull it and pass it over the idler wheel.

11. Tighten the screws of the flywheel cover plate.

12. Give supply to the motor and check if the belt rotates without any slipping in play, FF and REW modes.

13. Remove the supply and put a drop of wax or point at the fixing screws so as to avoid the loosening of

screws.

Result: Removed and fixed main belt of a tape recorder


72

Fault Finding of Tape Recorder


73

FAULT ANALYSIS OF TAPE RECORDER

Complaint: Dead Tape Recorder

Additional symptom: Tape not moving, No hissing sound from speaker (Max. volume), No indicators ON

POSSIBLE FAULTS CAUSES/ REASONS REMEDIAL MEASURES

Defective AC Power cord Low rating cord, mishandling, low quality

Replace power cord with suitable rating and flexibility

Battery voltage not reaching both mechanism and circuit

Dead cell, Corroded sell, rusted terminals, broken wire from cell to circuit

Replace new cell, clean terminals with sand paper, re solder wires

Defective ON/OFF switch on the mechanism

Open switch, corroded, ageing/mishandling

Replace with new switch

Defective power supply Defective components, Open connecting wires, Cut PCB tracks

Replace with good component of same specification, re solder joints, make joints b/w cut tracks

Complaint: No tape Movement

Additional Symptom: Neither take up nor supply wheel not moving, hissing noise heard from loud speaker (high

volume)


Slipped Main Belt

Loose belt Ageing, low quality belt Replace belt

Belt Cut Very tight belt used, low quality belt, belt touching some metallic portions while running

Replace belt

Worn out/Broken pulleys

Wobbling of pulley/fly wheel

Ageing, low quality, improper fitting Replace worn out pulleys, remove &refit pulleys/flywheel

Motor not Running

Open/dry solder at motor terminals

Ageing, improper soldering Remove and re solder wires

Open leaf switch Ageing, low quality, burnt contacts Replace leaf switch

Motor winding burnt Ageing, overloading, over voltage Replace motor

Open/broken supply wires to leaf switch/Motor

Ageing, dry soldering, mishandling Re solder/Repair wires

Jammed Fly wheel

Without any lubrication Ageing Lubricate with lubricants

Bent flywheel shaft Mishandling Remove/straighten bend

Jammed flywheel, shaft and bush

Ageing, due to rust Remove rust using fine sand paper

Excess tightness of fly wheel cover

Mishandling/negligence Loose the tightness


74


75

Complaint: No Fast Forward/Rewind

Additional Symptom: Sound okay when tape is played


No Fast Forward

Bend in spindle shaft Mishandling Remove/straighten bend and refit

No Contact/poor contact b/w spindle and drive

Worn out/broken rubber contact Remove/straighten bend and refit

Defective Fast Forward lever

Improper fitting, rough handling Remove and refit/replace lever

Loose Belt Ageing, low quality belt used, incorrect belt size used

Remove and replace with suitable size.

No Rewind

Bent supply reel spindle shaft

mishandling Remove/straighten the bend and refit

Defective rewind lever Improper fitting, rough handling Remove and refit/replace lever

No contact/Poor contact between spindle and drive

Worn out/Broken rubber contact Remove and refit rubber contact

Loose Belt Ageing, Low quality belt used, Incorrect belt size

Remove and replace with suitable size belt

Complaint: Tape getting jammed in Play and Record

Additional Symptom: Tape not getting jammed while fast forward and rewind


Defective Pinch Roller

Worn out pinch roller Ageing, low quality pinch roller Replace Pinch roller of good quality

Sticky pinch roller Low quality pressure rubbed in pinch roller

Replace Pinch roller of good quality

Defective Take up wheel

Worn out idler wheel rubber

Ageing Replace idler wheel

Take up wheel contact surface with idler with idler wheel rubber worn out

Bad quality take up wheel Replace take up wheel

Take up wheel jammed Dusty environment, Bad quality take up wheel

Replace take up wheel

Weak idler assembly tension spring

Ageing, bad quality Replace spring and complete idler assembly

Sticky capstan shaft Dusty/oily/greasy, rusted shaft

Replace fly wheel assembly


76


77

Complaint: No sound

Additional Symptom: Play mode tape movement okay


Defective Speaker

Open Voice Coil Over loading/ over voltage Replace speaker

Defective wire terminals Dry soldering Remove and re solder terminal wires

Defective Power Amplifier

Absence of power source Open series resistance, supply wires cut/open, shorted filter capacitor

Replace resistors, re solder supply wires, replace filter capacitor

No power amplifier output

No power amplifier input Open/short IC or circuit Cut/short shield wires

Rectify/replace IC or circuit Rectify/replace shield wire

Defective Volume Control

Poor soldering terminals Open/dry soldering Remove/re solder wires

Poor contact of moving parts Broken contacts, damaged carbon track

Replace volume control

Defective head pre amp

Absence of Power source Open series resistor, supply wires cut/open, shorted filter capacitor

Replace resistors, rectify/re solder wires, replace filter capacitor

No head pre amp output No head pre amp input

Open/short IC or circuit Cut/short shielded wires

Rectify/replace IC or circuit Rectify/replace wires

Defective R/P Head

Poor soldering, R/P head terminals

Open soldering Re solder terminals

No signal pick up Dusty R/P head Worn out R/P head

Clean R/P head using head cleaner, Replace head.


78

INSTALLATION OF A SURROUND SYSTEM


79

INSTALLATION OF A SURROUND SYSTEM

Aim: To install a surround system – Dolby (5.1)

Theory

Surround Sound

5.1 (5 speakers + subwoofer) A 5.1 surround-sound setup includes left, center and right front speakers. It also has left and right surround

speakers. Dolby Digital, Dolby Pro Logic II and DTS 5.1 will all support this format. DTS 96/24 uses a 5.1

channel format to play audio at the same sampling rate at which it was recorded. Woofer can be placed

anywhere in the room

6.1(6-7speakers+subwoofer)

A 6.1 setup takes all the speakers from 5.1 and adds a rear channel. Dolby Digital EX uses this format,

splitting the one additional channel into left and right rear speakers.

7.1 (7 speakers + subwoofer)

Dolby Pro Logic IIx has separate channels for the left and right rear speakers, rather than splitting one

channel and directing it to two speakers.

The sound system is what really makes a home theater experience complete.

Procedure

1. Place speakers at the front centre, front left, front right, rear left and rear right. 2. Place sub woofer at any position in the room. 3. Connect surround amplifier’s output to the corresponding speakers and woofer. 4. Connect the output of a DVD either through amplifier or directly to speakers. 5. Adjust the controls in the amp to obtain a good and an echo free sound.

Result

Set up a DOLBY surround (5.1) system in the room.


80


81

TELEVISION ANTENNA, TRANSMISSION LINES AND BOOSTER

Aim:

1. To study about Television Antenna, Transmission lines and Booster

2. To mount booster unit

Theory

TV antenna receives electromagnetic waves which are transmitted from TV station and convert them into electric currents. These currents are fed to TV receiver by means of transmission lines such as flat twin lead or co-axial cable. Antenna principle: Accelerated charge results in radiations. TV signals are transmitted as horizontal polarized waves.

Yagi Uda Antenna This is the most commonly used antenna in VHF range and it is to be pointed towards TV transmitting antenna for maximum signal pick up. It mainly consists of three elements – Reflector, Directors and Folded dipole. Antenna provides high directivity, wide band and high terminal impedance Reflector Reflector is placed beyond the folded dipole and it is about 5% more in length than dipole. Its main function is to reflect the signal coming from the front side of the antenna towards dipole and to reject signals coming from other sides. By using reflector,

a) The signal strength at the dipole increases b) The directivity of the antenna improves c) Possibility of ghost picture avoided

Dipole Dipole is constructed by folding an aluminum rod. Feeder is connected to its open ends and extends to TV. Transmission feeder is connected to its open end and extended to TV. The length of the dipole is kept almost equal to the wavelength of the channel for which it is meant. Director These rods direct the signal towards folded dipole. They are the smallest among these three elements.

Television booster (VHF) Booster is just an amplifier which is commonly used to amplify the weak RF signals received by the antenna before feeding it to the receiver. The entire unit consists of two sub units

a. Power supply unit b. Amplifier unit.


82

BALUN

Observation

Output voltage from the booster power supply unit to the antenna = …………..V (ac)

Biasing voltages of transistors/ FETs used in the amplifier section

1.


83

Power supply is normally placed near to Television receiver. The unit generates ac voltage of about 18 to 22 Volts and feed it to the amplifier section kept near the antenna through the feeder wire. The booster control placed in the power supply is used for varying the ac voltage supplied to the booster amplifier. It is from this unit that the signal coming from the antenna is directed towards receiver through capacitors of 0.01 MF each.

The amplifier unit consists of two BALUN s– each at the input and at the output for impedance matching, a rectifier unit to rectify the ac voltages reaching from the power supply unit and 3 or 4 stages of amplification (transistors or FET). Power from the power supply and the signals amplified by the amplifier are carried through the same feeder. Procedure

1. After removing the case of power supply unit, sketch the circuit of the unit. 2. Identify the components used in this section. 3. Similarly sketch the circuit of amplifier unit and identify the components used in it. 4. Connect both units by means of a twin lead feeder wire. 5. Switch on the power supply unit and measure voltage at the output of the unit. 6. Note the changes in the supply when booster control is varied. 7. Measure the biasing voltages at different terminals of transistor/FET in the amplifier section and

mark them.

Booster Mounting Procedure:

1. Keep the power supply unit of the booster unit near the TV and connect the booster amplifier to the supply unit via a feeder line.

2. If the picture and sound quantities are not good, adjust the booster control to get best results. 3. Always use the BALUN to connect feeder wire of 300 Ω (flat twin lead) to the RF amplifier of

tuner (75 Ω). If BALUN is not used, impedances do not match and reflections may occur causing Ghost images. If co-axial cable is used for interconnecting antenna terminals with tuner, no need of BALUN since both the impedances are 75 ohms.

Transmission lines Wave Guide: Usually used for carrying high power RF. Example – Radar. It offers less loss, but

handling is difficult

1. Co –axial cable: Characteristic impedance - 75 Ω. No need of BALUN for connecting this to RF amplifier of tuner

2. Flat twin lead: Characteristic impedance - 300 Ω. BALUN is used to connect this to RF amplifier(75 Ω) to match the impedances

Result: Studied about television antenna, booster and transmission lines Learned how to mount Television Antenna.


84

PATTERN GENERATOR


85

PATTERN GENERATOR Aim: To perform the alignment of Television Receiver using Pattern Generator Theory Pattern Generator provides video signals direct and with RF modulation on standard TV channels for alignment, testing and servicing of TV receiver. PG produces different patterns which enables the service technician to check the performance of TV receiver even when the TV station is not ON. The patterns are produced with the help of multivibrators and wave shaping circuits. The RF modulated by the selected pattern is fed to television receiver and the output is viewed on the fluorescent screen to determine various faults of monochrome and colour TV receivers. Pattern generator also has the provision of testing the audio section of television receiver. A 1 KHz tone generator modulates the 5.5MHz carrier frequency using frequency modulation method. This signal goes to the inter carrier frequency amplifier (2nd IF amplifier) in the TV receiver and is processed to reproduce sound from loud speaker. Different controls of PG (Sanwa PG 301)

1. Pattern selector switch

We can select the desired pattern by this switch. We get six different types of patterns from this generator

2. Band selection switch By this switch, we can select the signal of the desired band. If we want RF signals on channels 2, 3 and 4, we have to push this switch on band 1. If we want signals on channels 5 to 12, we have to push selector switch on band III

Patterns produced by this PG

a. Dot Pattern The pattern appears in the form of dots. This pattern is useful when the focus of the picture is to be adjusted. Fine and clear dots indicate proper focusing of picture while adjusting. There are 15 vertical dots and 19 horizontal dots produced by this PG

b. Cross hatched Pattern This pattern indicates whether the horizontal and vertical scanning of the picture is proper or not. These squares should be equal if the TV set is good. This pattern is also used to adjust the yoke coil.

c. Horizontal line pattern If the lines that appears on the raster are not parallel and the distance between the lines are not equal, the centering magnets of the yoke coil has to be adjusted and correct pattern has to be obtained.

d. Vertical line pattern If the vertical lines are not straight, both the centering and ring magnets have to be adjusted to make them straight


86


87

For the proper alignment of centering magnets, both the vertical and horizontal line patterns are necessary.

e. Colour Pattern Colour pattern generator generates colour for colour TV receivers. We can check the purity of the colour of the picture by this pattern

f. White Pattern To adjust white level in colour TV, this pattern is utilized. The raster in the screen should appear white when this pattern is applied. The white level adjustment should be proper in order to obtain natural colours.

Procedure

1. Use horizontal bars to check vertical linearity. If the bars are straight and are equally spaced, we can say that the vertical linearity of the receiver is good.

2. V-bar pattern checks horizontal linearity. If the lines are equally spaced, horizontal linearity of the receiver is good.

3. Cross hatched pattern easily allows both the horizontal and vertical deflection circuits. 4. If the pattern rolls up or down, it shows lack of synchronization of the vertical sweep generator

with the vertical sync pulse. 5. If the pattern shows diagonal splitting, it reflects lack of horizontal sweep circuit with horizontal

sync pulse. 6. Cross – hatch pattern allows checking of centering and aspect ratio. This is done by counting the

number of squares on the vertical and horizontal sides of the screen. 7. As the RF modulated signal is available, the working of RF and IF sections can be checked. 8. Sound IF, limiter, discriminator and audio circuits can be checked by using FM signal of the Pattern

Generator. 9. It can be used for fault diagnosis of TV receiver.

Result:

1. Studied about the pattern generator. 2. Carried out the alignment of TV receiver with it


88

TELEVISION BROAD CAST CHANNELS Band I - Lower VHF range - 41 MHz to 68 MHz Band III – Upper VHF range – 174 MHz to 230 MHz Band IV – UHF Range - 470 MHz to 582 MHz Band V -UHF Range - 606 MHz to 890 MHz TELEVISION CHANNEL ALLOCATION IN BANDS I AND III

BAND CHANNEL

FREQUENCY RANGE (MHz)

PICTURE CARRIER FREQUENCY (MHz)

SOUND CARRIER FREQUENCY (MHz)

OSCILLATOR FREQUENCY (MHz)

I (41 – 68 MHz)

1

2

3

4

III (174 – 230 MHz)

5

6

7

8

9

10

11

12

IV (UHF) 470 – 582MHz

13

14

15 to 28


89

BLOCK SCHEMATIC OF TEXLA TELEVISION KIT

TELEVISION ANTENNA CHECK

For checking the TV antenna, disconnect the feeder wire from the antenna socket and measure

the resistance between wires.

If the resistance between wires is in between 3 ohm and 5 ohm, Antenna is good.

If the resistance between wires is less than 3 ohms, antenna is short

If the resistance between wires is above 5 ohms, antenna is bad.

Result

Measured the resistance between wires.

Resistance between the leads is …….ohms

Antenna is …………….(good/ bad)


90

TELEVISION TUNER (TURRET TYPE)


91

TUNER (TURRET TYPE) Objectives

1. Note the antenna input, B+ supply and AGC coils in tuner box 2. Inject a pattern generator at the input point and observe different patterns on screen. 3. Measure AGC voltage in the box (Note the AGC voltage when the antenna is connected and

removed. There should be a rise in voltage when antenna is introduced)

Theory Tuner tunes the desired channel and converts it into two IF frequencies – Picture IF of 38.9MHz and Sound IF of 33.4 MHz

Turret tuner is a 12 channel unit contained in a metal box. It covers the channels 1 to 4 on Band I and channels 5 to 12 on Band III. This unit has a channel selector switch and a fine tuning control. The fine tuning control is intended for correctly adjusting the RF oscillator frequency in order to get correct IF frequencies (Picture IF of 38.9 MHz and sound IF of 33.4 MHz). This unit is fed with 11.5 V obtained from the 12 V dc line. The IF output from the tuner is fed to pin 6 of IC CA3068. AGC preset is provided for setting the threshold of AGC operation. Tuner consists of an RF amplifier circuit, a mixer circuit and an oscillator circuit. Signals tuned by the antenna circuit are fed to mixer where it gets mixed with the signals obtained from the local oscillator and as a result, the new frequencies (Picture IF of 38.9MHz and Sound IF of 33.4 MHz) are produced. Internal Structure of Tuner Tuner has a shaft with 4 drums attached to it. 12 coils for 12 channels are fixed on each drum. Shaft, drums and 48 coils rotate together by turning the knob. For any position of the knob, a set of 4 coils comes in contact with 4 circuits of the tuner. If the knob is on 7, then signals of channel 7 only can pass through the tuner. When knob is turned further, another set of 4 coils comes in contact with 4 circuits of the tuner, and any one out of 12 channels can be selected by the tuner Result

1. Noted the antenna input points. 2. By connecting pattern generator at the input point of the tuner, observed different patterns on

screen 3. Measured the B+ and AGC voltage

B+ Voltage = AGC Voltage =


92

310C1P4 AND 470 C1P4

500C1P4, 590 C1P4 AND 590 C1P4

Picture Tube Yoke


93

MONOCHROME PICTURE TUBE SPECIFICATIONS Aim: To measure neck voltages of different monochrome picture tubes The commonly used picture tubes are 310C1P4, 470C1P4, 500C1P4 and 610C1P4. The first three letters indicates the picture tube size in mm. All these picture tubes employ electrostatic focusing and electromagnetic deflection. Pin Connection All picture tubes have 8 pin base. The gap between all these pins are almost equal, but there is a key position between 1 and 8. From this key position, all pins are counted in clock wise direction.

310C1P4 AND 470 C1P4

SL.NO PINS VOLTAGES OBSERVED

1 FILAMENT 3 & 4

2 CATHODE 2

3 CONTROLGRID 5 & 1

4 ACCELERATING GRID 6

5 FOCUSSING GRID 7

6 NO CONNECTION 8

500C1P4, 590 C1P4 AND 590 C1P4

SL.NO PINS Typical voltages

VOLTAGES OBSERVED

1 FILAMENT (AC RANGE) 1 & 8 6.3V ac

2 CATHODE 7 75V

3 CONTROLGRID 2 &6 -ve to 40V

4 ACCELERATING GRID 3 160V

5 FOCUSSING GRID 4 0

6 NO CONNECTION (GND) 5 0

Result: Measured neck voltages of different picture tubes


94


95

TELEVISION POWER SUPPLY (TRANSFORMER POWER SUPPLY) – TEXLA KIT(20”) Objective To study and test the power supply section of a TV receiver a) Check B+ power supply 140V at dc fuse point b) Check B+ fed voltages for the different sections of TV receiver. c) Observe whether picture tune is glowing or not Theory Usually transformer power supply is used in texla television kits. As in the figure, three outputs are obtained in TEXLA power supply. For this, a step down transformer with three separate windings is used. The winding 0 to 150V is the high voltage winding, 0 to 15V is the low voltage winding and 0 to 6.3V is the winding that provides filament voltage to CRT.

150V ac (high voltage supply) available in the secondary winding of the transformer is rectified by a bridge rectifier and is filtered by a filter network. RC filter network consist of 2 capacitors (100+100MFD/350V) and a 100Ω/35 Watt resistor. 15V ac obtained from another winding of the secondary is also rectified and filtered by an RC filter consisting of 1000MFD/25V capacitor and a resistor of 1Ω/1W. The sync separator, AFC, horizontal oscillator, sound IF and sound output section are fed from this low voltage power supply. 6.3V ac obtained from a separate winding of the secondary is fed to the filament of CRT Other supplies of TV DC supplies of 150 V and 12V become available after 230V ac supply is given to TV. The two dc supplies reach the points as shown in the figure. Few seconds after the arrival of 14V supply at pin 1 of IC CA920, the pulses of 15625 Hz are formed which reach the horizontal output section. Now, LOT produces pulses of 18KV, 500V boosted power supply, 35V and 15V regulated dc power supply. In the absence of 15625 Hz pulses, neither the raster nor the regulated supply can be obtained. The pulses available at pin 5 of LOT are rectified to get 35V dc. This supply is sent to TDA 1044 in vertical section, to the blanking transistor BC 147 in video section and to the transistor AC 187 to obtain 15V regulated supply. 15 V supply is sent to tuner, video IF board, BF 195, video section, BC 148 and to pins 1 and 8 of IC, CA 920. Result Studied and tested the power supply section of TV receiver.


96

Video IF Amplifier

Pins Functions Voltage Voltage measured

1 Ground connected to metal shield of IC 0 V

2 5.5 MHz inter carrier sound output 5 V

3 Keying pulses obtained from LOT 0.6 V

4 Keyed AGC output -2 V

5 Ground 0 V

6 Input of 1st video IF stage from tuner 2 V

7 RF AGC output for Tuner 9 V

8 AGC delay is controlled by applying stable positive voltage to these pins

0.8 V

9 First Video IF collector voltage 7 V

10 Ground 0 V

11 No connection NC

12 Tuned circuit of sound IF connected to this pin 1.6 V

13 Base of second video IF 1.6 V

14 Position for fine tuning (not used here)

15 Supply 12 V

16 Bias obtained internally to sound IF tuned circuit at pin 13 1.6 V

17 Ground 0 V

18 Regulated Power Supply 11 V

19 Video output signal to video Amp 4.4 V

20 No connection


97

VIDEO IF SUB SECTION Objective To study and test video IF and AGC sections

a) Identify the ICs and components used in this section b) Check pin voltages to CA 3068 and record c) Check the proper functioning of AGC in this section

Functions In Tesla circuit, IC CA3068 performs the function of IF amplification, video detector and AGC generator. Prior to video IF stage, wave traps are provided to attenuate certain frequencies. 1. To amplify very low volt IF signals coming from tuner. 2. It detects the video signals from the amplitude modulated video IF signals of 38.9 MHz coming

from the tuner 3. The section does not separate audio signals from IF signals, but converts 33.4 MHz sound IF

signals to 5.5 MHz sound IF signals. Separation of audio signals from these low frequency 5.5 MHz SIF signals becomes easy.

4. Video pre amplifier provides a low level amplification for the video signal developed at the output of video detector.

5. A portion of CVS from the output is applied to the AGC generator which develops control voltage for RF and IF stages

Working CA 3068 is a 20 pin IC. The signal obtained from RF tuner is passed to pin 6 of IF IC CA 3068. Trap circuits placed before the IC eliminates different interferences and allows only the IF to reach the IC. This IC amplifies the two Ifs to a level of nearly 5Vpp from the input level of 1mV at the tuner output. Video signals obtained from pin 19 of the IC and sound IF of 5.5 MHz is obtained from pin 2 of the IC. AGC voltage is obtained from pin 7 which is converted to forward AGC by BC 548B and then fed to RF amplifier stage of RF tuner. The IC operates from a 12 V dc applied at pin 15 of the IC. The base of BC 548B is kept at a positive bias by means of 1.2 KΩ resistor. The transistor can operate only when the voltage of the input signal is higher than the base bias voltage

The input amplifier of IC is biased at pin 4 by a potential divider network. A keying current of about 0.8mA is applied from LOT for AGC generator. The amplified and detected video signal and the newly generated inter carrier sound IF of 5.5MHz are tapped off from pin. 19

Features

1. Three stages of video IF amplification 2. Provision of both keyed and delayed AGC 3. Video signal pre amplification 4. Video detection 5. Generation of sound IF


98


99

Procedure

1. Study the circuit of video IF board, components. 2. Check the voltages on different pins of the IC by a multimeter.

Precaution 1. Don’t touch the setting of pre-sets and contrast control 2. Obtain the guidance of your teacher/instructor for connecting instruments 3. Do not forget to connect earth leads of the instrument to the chassis of TV receiver.

Result

Studied and tested the video IF and AGC sections


100

SOUND SECTION TBA 120S – S.IF Amplifier, FM Detector, AF Amplifier

Pins Function Typical Voltage

Voltage measured

1 Ground 0

2 Feed back (de coupling capacitor) 1.9

3 Ground 0

4 Ground 0

5 Electronic volume control 3.8

6 FM detector

7 FM Detector 3.3

8 Audio output 4

9 FM Detector 3.3

10 FM detector

11 +Ve supply voltage 11

12 Ground 0

13 Sound IF signal from video detector 1.9

14 Sound IF signal from video detector 1.9

TBA 810– Power Amplifier


Voltage measured

1 +Ve supply voltage 12

2 N/C N/C

3 N/C N/C

4 Ground 0

5 Ground 0

6 Boot strap 12

7 Compensation 0.6

8 Feed back (output to input) 1.4

9 Ripple rejection 6.2

10 Audio input 0.3

11 Negative voltage 0

12 Ground 0

13 Ground 0

14 Ground 0

15 N/C N/C

16 Audio output 6.5


101

SOUND IF AND OUTPUT SECTIONS OF A TV RECEIVER

Objectives

1. Identify the ICs used in this section and components

2. Check pin voltages of these ICs and record

Theory

ICs, CA920 and TBA 810 are used in the sound section of TESLA television. CA 120 recovers audio

signals from sound IF signals. TBA 810 amplifies these signals and gives them to loud speaker

Signals coming from pin 19 of IC CA3068 are sent to the primary of sound IF transformer through a

capacitor 6.8PF. As the primary and secondary coils sound IF transformers are tuned to 5.5MHz, video

signals cannot reach the secondary of this transformer

Audio IF amplifier, IC TBA 120S

This sub system consists of an IC, TBA 120 S which performs the functions of sound IF amplifier,

limiter, FM detector, attenuator and audio driver. This IC also has built in power supply to provide power

to different stages inside the IC. The operating potential of this IC is provided at pin 11 wrt pins 1, 3, 4 and

12.

From the secondary of the trap circuit, sound IF signals are applied to pins 13 and 14 of IC

TBA120S. Output of IC is available at pin 8. Inductor and capacitor connected in parallel across pins 7 and

9 does the job of FM detection. Limiter stage eliminates all amplitude variations due to noise pulses from

FM sound signal. Audio signals from pin 8 is sent to volume control present on the outer panel of the TV.

The other end of the volume control is connected to the ground of PCB.

Other ICs that can be used as sound IF and detector are TAA 570, CA 3065 and TBA 750


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Audio Amplifier, TBA 810

The detected audio signal from audio IF amplifier is applied to the input of IC at pin 8 through a volume

control. This IC performs the functions of voltage amplifier and power amplifier. The working potential of

IC is applied at pins 1 and 4 with respect to pins 9 and 10. The amplified output developed at pin 12 is fed

to the loud speaker. The loud speaker converts audio signals into corresponding sound wave.

CA 810 carries a heat sink for heat dissipation. It delivers an audio output of about 4 Watts at its

pin 12, which is coupled to an 8 ohm impedance loud speaker through a 1000MFD condenser. Both the

ICs are wired separately on the same PCB mounted on the main board supply.

Result

Studied about the sound section of Texla Kit

Sketched voltages at different pins of 120 S and 810


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ADJUSTMENTS IN TELEVISION RECEIVER Aim To study various adjustments in a TV receiver

Servicing Controls : (Mono Chrome) Theory Height Control It is to adjust the height of the picture. It is done by varying the amplitude of the vertical pulses. In our receiver, this control is a 1 K preset incorporated in the dc biasing circuit between pin 7 and 1 of vertical IC, TDA 1044. While adjusting this preset, dc bias to saw tooth generator is varied and hence the amplitude of the saw tooth pulses also varies. Vertical Linearity Control

This control is to check the linearity of the picture. It is achieved by varying the shape of the vertical saw tooth pulses. In our circuit, it is a 100K preset connected to pin No. 1 of the vertical IC – TDA 1044. If the picture is not uniform in the vertical direction, it is the result of vertical non-linearity which can be corrected by the vertical linearity control. This control either varies the cathode bias on the vertical amplifier or it controls the amount of feedback in the vertical circuit Horizontal Hold Control This control in a TV receiver varies the horizontal oscillator frequency. In the circuit, it is a 15K preset connected between pin. No 15 of horizontal IC, CA 920. Vertical Hold Control V.Hold varies the frequency of vertical oscillator. Usually, this is a 100 K preset connected to pin no.11 of the vertical IC, TDA 1044. AGC level This control is to set the delay for the AGC voltage. It is provided in the AGC line to the tuner. It is a 47K preset connected between pins 8 and 7 of the video IF IC, CA 3068. Volume Control: Controls the volume of the TV receiver Contrast Control Varies the amplitude of the video signal. On varying this control, bright parts become more bright and dark parts become more dark. Brightness Control Changes the overall brightness of the scene that is being televised.

Picture position and centering control: Picture tubes are fitted with a pair of deflection coils for horizontal and vertical deflection of the electron beam. The entire yoke can be turned round in its housing there by shifting the raster. For centering of the picture, the yoke coil is fitted with two magnetic discs or rings which can either be rotated together or with respect to each other so that the beam can be moved horizontally, vertically or any other angle. The magnetic rings are first moved together to the best position of the picture on the screen is obtained. The magnetic rings are then rotated with respect to each other till the raster or the picture is properly centered.

Result Studied about different controls used in TEXLA kit. Examined the changes in picture and sound when each control was varied.


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ICS AND TRANSISTORS USED IN DIFFERENT SECTION OF TEXLA KIT Aim: To study about different ICs and Transistors used in different sections of TV receiver Theory 1. Horizontal Section

a. BC 148A - Sync Amplifier b. TBA 920 - Horizontal Oscillator, AFC, Sync Separator

2. Vertical Section a. TDA 1044 - Vertical Oscillator, Vertical Amplifier

b. BC 147B - Blanking Transistor

3. Video Amplifier Section a. BF 195C - Video Driver Transistor b. BD 115 - Video Output Transistor c. BC 147B - Blanking Transistor

4. Video IF Section

a. CA3068 - Video IF Amplifier, Video Detector, AGC b. BC 158B - RF AGC Transistor

5. Sound Section

a. TBA 120S - Sound IF Amplifier, FM Detector b. TBA 810 - Voltage Amplifier, Power Amplifier

6. Horizontal output Section a. BD 115 - Horizontal Driver b. BU 208 - Horizontal Output Transistor

Result Studied about different Transistors and ICs used in Texla Kit


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Horizontal section of TEXLA television


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Horizontal output section of TEXLA television

Aim: To study about horizontal output section of Picture Tube.

Horizontal Output section

The main functions are,

1. To provide a current of suitable waveform for horizontal deflection coil. 2. To supply a high voltage of about 18 KV for final anode of CRT. 3. To provide a high voltage of about 250 V known as boosted voltage to accelerating anode. 4. To provide 6.3 V AC to CRT heater. 5. To provide different low voltage auxiliary power supplies for different stages of the receiver 6. To provide fly back pulses for horizontal oscillator to synchronize the phase and frequency of

horizontal signal with the incoming signal 7. Provide keying pulses for AGC generator in video IF sub system 8. Horizontal blanking pulses to blank out the CRT during horizontal retrace.

Driver transformer, Line output transformer (EHT), two transistors – BD115 and BU 205 are used in horizontal output section of Texla Television. 150V dc supply is given to the collectors of both transistors.

15625 Hz saw tooth waveform available from pin 2 of IC CA 920 is fed to the base of the driver transformer, BD 115 through the coupling capacitor 4.7MF and 56 ohm resistor network. The amplified pulses reaches the collector and primary of the driver transformer. From secondary of the transformer, the pulses pass through a resistance and coil and reach the base of transistor BU 205. Pulses of different volts are produced and different winding of LOT attached to the collector of BU 205. The different pulses are used for different functions as explained below.

Pulses of pin no. 2 of EHT

These pulses perform the main function of horizontal output section. The pulses passing through a capacitor reach a resistance and a linearity coil. From here, the pulses reach the yoke present on the neck of picture tube and start the horizontal trace and retrace of electron beam.]

The width of raster and shape of picture in horizontal direction can be slightly increased or decreased by rotating the core of linearity coil.

Pulses of pin no.3 of EHT

The pulses are changed to boost dc supply with the help of a diode. The capacitor of 0.002MFD present between the boosted supply and 150V dc supply is used to filter the boosted supply. Through 2 resistors, boosted supply is given to the accelerating anode of picture tube, i.e., to pin No. 3 of picture tube.


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Pulses of Pin No.9 The pulses are used for the following two functions

1. Through a capacitor, the pulses are given to the accelerating anode of picture tube. It stops the ejection of electron beam to a horizontal beam during the horizontal retrace time, i.e., the pulses perform the work of horizontal blanking

2. With the help of a diode and capacitor, the pulses are converted to a supply of 35Vdc. This supply is used in vertical section and video section. This supply is also given to transistor AC187 and a zener diode 15VZ to obtain a regulated supply of 12V

PULSES OF PIN 5 The pulses are used as fly back pulses and are sent to pin 5 of IC CA 3068. Pulses of EHT winding EHT winding contains a very large number of turns and pulses of about 18KV develop in this winding. These high voltage pulses are rectified by TV20 and 18KV dc supply is obtained. The EHT supply is given to a socket on the picture tube and reaches the inner conductive coating on the glass of picture tube. The other conductive coating present on the outside of the glass is connected to ground. The two conducting coating and the glass present between them and as a filter capacitor of very large capacity. The filter capacitor converts fluctuating dc coming from TV20 to pure dc of 18KV. Result Studied about horizontal output section of Texla TV receiver.


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VERTICAL OSCILLATOR AND OUTPUT - TDA 1044

TDA 1044– Vertical Oscillator, Vertical output, Vertical Blanking Generator


Voltage measured

1 Geometrical distortion circuit to improve vertical linearity 3.4

2 Feed Back 3.8

3 Feed back 0.8

4 50Hz frequency output to vertical deflection coil 6

5 Positive supply to final V. Amplifier 18

6 Vertical blanking generator (50Hz) 1

7 Positive supply from EHT section 18

8 Vertical sync input from sync separator 0

9 Not connected in the circuit N/C

10 Vertical Oscillator – 50Hz 1

11 V. Oscillator control, V- Hold 6

12 Vertical Oscillator supply 7


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VERTICAL OSCILLATOR AND OUTPUT - TDA 1044 Objective 1. Identify ICs used in this section 2. Conduct a check to know the goodness of this section – vary V-hold control and see whether

picture rolling takes place and then lock it to a steady picture. 3. Vary height and linearity controls and see how the picture is affected. Set it right. 4. Check pin voltages of TDA 1044 and record. 5. Check ac and dc voltages on vertical deflection coil and record.

Theory

The main functions of this section are,

1. Generation of vertical sweep frequency of 50 cycles/second 2. To amplify the signal sufficiently to drive vertical deflection unit 3. To keep the vertical sweep of the receiver in lock with the transmitted vertical sweep 4. To provide vertical sync pulses and blanking pulses to synchronize and blank out in CRT during

vertical trace and retrace periods respectively.

The vertical oscillator and output stage drives from 40V dc obtained from an auxiliary power supply in the horizontal output stage of the receiver. The vertical synchronizing pulses are applied to pin 8 of IC TDA 1044 through an integrating circuit from pin No.7 of IC, CA 920. This synchronizing pulse keeps the vertical sweep frequency in lock with transmitted vertical sweep.

By varying the vertical hold control, the oscillator frequency could be changed. The picture height can be adjusted by varying the vertical height Control. The vertical output will be developed at pin no.4 and it is fed to the vertical deflection coil through an electrolytic coupling capacitor.

Result

Studied about vertical oscillator and output sections of Texla Kit.

Checked pin voltages of TDA 1044 and recorded.


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HORIZONTAL OSCILLATOR

Pins Functions Voltage Voltage

measured

1 Dc supply from zener diode - regulated 12 V

2 Output of horizontal oscillator to drive horizontal output stage 4.2V

3 Pulse shaper and Phase shifter 2.4V

4 Oscillator phase control voltage (Phase discriminator)(APC) 2.4V

5 Horizontal fly back pulse from LOT for phase correction -0.2V

6 Horizontal Sync Pulses 0V

7 Sync pulses (horizontal and vertical) 1 to 7

8 Composite video signal input 0.2V

9 Noise Gating (Not Used) 0V

10 Filter network for controlled voltage at pin 4 2.6V

11 Oscillator frequency (Time constant switching) 3.2V

12 Control current which is passed to pin 15 1.4V

13 Oscillator reference voltage 7.5V

14 Oscillator frequency determining network 7V

15 Horizontal hold control 3V

16 Earth 0V


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SYNC SEPARATOR AND HORIZONTAL OSCILLATOR, TBA 920 Objective

a) To identify ICs used in this section and its components – driver transformer, LOT etc. b) Check the goodness of this section

1. Vary H hold and observe diagonal lines on screen 2. Take biasing voltages of BC 148 B and record.

The main functions are,

1. Separation of sync pulses from composite video signal 2. Generation of 15625 Hz 3. To keep the phase and frequency of horizontal oscillator in lock with transmitted horizontal sweep

with reference to the horizontal sync pulses. 4. Shaping the oscillator output to obtain pulses capable to drive horizontal output circuit

Sync Separator Pins 6, 7 and 8 of IC CA920 and transistor BC148 are used in separating the sync signals from video signals. CVS coming out from pin no.19 of IC CA 3068 are sent to the base of transistor BC148. The sync signals after amplification in the IC come out at pin 7 are sent to integrator and differentiator circuit Only vertical sync pulses get integrated in integrator circuit. The integrator signal are sent to pin 8 of IC, TDA 1044 to synchronize the frequency of horizontal oscillator Horizontal oscillator and horizontal hold The frequency of horizontal oscillator pulses coming out of pin 2 of IC CA920 depends on the value of capacitor attached to pin 14 and the value of resistance attached to pin 15. The frequency can be changed by changing the preset attached to pin 15. The preset is called horizontal hold. Fly back pulse From pin no.2 of IC CA920, horizontal pulses reach the base of BD115. Fly back pulses of same hertz come back to pin 5 of same IC. IC compares the frequency of these fly back pulses with 15625 Hz horizontal sync pulses. If there exist a difference among these frequency, IC gives a control voltage on its pin 11. This control voltage reach pin 12 and 15 and forces the frequency of pulses coming at pin 2 to remain at 15625Hz. DC supplies Both the 15V dc supply from the rectifier circuit and regulated dc supply from the EHT section are given to pin no1 of IC, CA 920 through separate diodes. The cathode of two diodes are joined together 12V regulated supply is also given to the collector of BC148. The supply is also given to pin 8 of IC CA 920 through a resistance of 2.2 Mega ohms. Result Studied about sync separator and horizontal oscillator. Measured voltages at different pins of IC.


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VIDEO AMPLIFIER AND PICTURE TUBE SECTION

]


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VIDEO AMPLIFIER AND PICTURE TUBE SECTION Objective To study video amplifier and picture tube biasing sections

a) Check brightness control for goodness b) Check contrast control for goodness c) Take biasing voltages of BD 115 and record.

Theory Functions of video section

1. It separates 5.5 MHZ sound IF signal from video signal 2. It sends the amplified video signals to the cathode of picture tube.

Video section amplifies the video signals obtained from pin 19 of IC CA3068 and gives these signals to the cathode of picture tube. This section is wired on a separate PCB and mounted on the main board at its middle right hand corner. Since the video band is large, the amplifier stage is to be specially designed to perform uniform amplification for all frequencies. An output signal of about 60Vpp develops at the collector of final video amplifier transistor, BD115. Beam current limiting diode, 1N 4003 is used between the collector circuit of BD 115 and the cathode of picture tube.

The CVS from the video IF amplifier is applied to the base of the transistor, BF195. A trap circuit made of a coil and capacitor joined in parallel is present at the emitter of this transistor to attenuate 5.5 MHz inter carrier sound signal. Only video signals appear at the output of this trap circuit. Presence of 5.5 MHz inter carrier sound IF at the output appear as sound bars on CRT screen. This transistor is used in the emitter follower configuration for getting the maximum output.

The video signal at the output of the driver transistor is applied to the base of final video amplifier transistor, BD115 through contrast control. Amplified video signals become available at the collector of BD115 and these signals are then fed to the cathode of CRT via a parallel combination of a diode, 1N4148 and a capacitor, 220KPF. The amount of video signals determines the picture contrast. It is in turn decided by the setting of contrast control. Transistor BD115 is a wide range high gain amplifier

Vertical blanking pulses of about 40Vpp coming from 6th pin of IC 1044 is applied to the base of BC147B (blanking transistor). On the arrival of blanking pulses, BC147 starts conduction and develop a voltage across emitter bias resistance of BD115. The signal voltage developed at the emitter of BD115 will be sufficient to cut off its conduction and hence blank out the CRT during vertical retrace period

At the time of horizontal retrace, blanking pulses are sent from pin 5 of LOT to pin 3 of picture tube.

DC supplies of video section 3 dc supplies of 150V, 35V and 15V regulated are given to the video section of TESLA TV. 150V supply is given to the collector of BD115 through a resistance of 5.6K 35V supply is given to the collector of blanking transistor BC147 through a resistance of 1K 15V regulated supply is sent to the base of BF195 through a resistance of 10K and 4.7K. It is also sent to the collector of BF195 and to the contrast control Result Studied about Video Amplifier and picture tube biasing section.


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ICs used in Daewoo Kit – 14”

Aim: To measure pin voltages of different ICs used in Daewoo Kit

µPC 1366 Functions: Video IF amplifier, Video Detector, Video Amplifier, AGC generator


1 Video Detector 8.9V

2 Fly back (blanking) pulse (15625Hz) input for IF AGC generator 1V

3 Composite video signal output 3.2V

4 AGC time constant 1.9V

5 RF AGC adjustment 6.3V

6 Delayed AGC control output to tuner 3.6V

7 Positive supply voltage 11V

8 Video IF input 5.7V

9 Video IF input 5.7V

10 Video IF Amplifier 5.7V

11 Video IF Amplifier 5.8V

12 Positive supply voltage 7.3V

13 Ground 0V

14 Video Detector 8.9V

µPC 1353C Functions: Sound IF and audio output, FM detector, Electronic attenuator


1 Squelch 9.8V

2 FM detector coil 4.8V

3 Electronic attenuator (de coupling capacitor) 5.9V

4 Detected audio signal output from FM detector 5.2V

5 Supply for sound IF section 8.4V

6 De coupling capacitor (for improving sound quality) 7.9V

7 Detected audio signal input 3.8V

8 Audio signal output to speaker 7.8V

9 Boot strap capacitor (to increase sound quality) 15.8V

10 Positive supply for audio section 19.3V

11 Feed back circuit to improve sound quality 7.8V

12 Sound IF signal input, 5.5 MHz 2.4V

13 Sound IF signal input, 5.5 MHz 2.4V

14 Volume control (electronic attenuator) 0.1V

Note: Ground with heat sink


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µPC 1031 Functions: Vertical oscillator, Vertical output, Vertical blanking generator, Vertical sync Amp


1 Vertical output (50Hz) to vertical deflection coil 9V

2 Positive supply for IC output section 18V

3 Vertical output (50Hz) to vertical deflection coil 16V

4 50Hz output from vertical oscillator and vertical sync amplifier (Height control)

15V

5 Vertical sync input (50Hz) from sync separator 1.2V

6 Vertical frequency adjustment, V-hold 4V

7 50 Hz input for vertical output stage (internal) 5.1V

8 Ground 0V

9 Feed back to improve vertical linearity 9V

10 Positive supply to IC 18V

Result: Measured pin voltages of ICs used in Daewoo Kit.


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Operating Controls of ColourTelevision Receiver

Aim:

To operate controls of Television Receiver.

Theory:

Common controls of a CTV receiver are,

1.ON/OFF Switch

2. Channel selector (Programme Selector)

3. Fine Tuning Control

4. Brightness Control

5. Contrast control

6. Colour control

7. Volume Control

8. Tone Control

9. V-hold

1. ON/OFF Switch: Mains supply to the receiver can be connected or disconnected with this switch.

2. Channel – Selector: Selects desired programme on desired channel. Push button channel selectors are commonly used for selecting programme on desired channel. In these, the tuned circuits connected with each push button can be tuned for any one of the channels and thus each of these can be pre-set to receive signals from any one of the desired channels.

3. Fine tuning control: Fine tuning control is provided to enable the viewer to tune the receiver exactly to the desired channel. Adjusting the fine tuning control make changes in the oscillator

frequency permitting accurate tuning.

4.Brightness Control: This control controls the average brightness of the picture. It adds or subtracts an offset, or bias, into the red, green, and blue signals. This control should be adjusted so that black picture content displays as true black on your monitor. Misadjustment of this control is the most common problem of poor quality picture

reproduction on computer monitors, video monitors, and television sets. The setting is somewhat dependent upon ambient light. Modern display equipment is sufficiently stable that frequent adjustment is unnecessary.


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5. Contrast control: Following symbol indicates contrast control. The level of luminance signals given to the picture tube cathodes depends on the setting of this control. It controls the

amplification of signals in video amplifier.

6. Colour control: The level of colour signals given to the cathodes of picture tube depends on the setting of this control. Thus colour intensity of the picture can be adjusted with it.

7. Volume Control: Level of sound signals can be controlled by this control

8. Tone control: Tone of sound cab be adjusted by this control

9. V-Hold: used for adjusting the vertical frequency to 50Hz.

Procedure:

1. Switch ON the television receiver

2. Select the desired channel with channel selector switch.

3. Adjust the volume control and tone control for the desired sound level and most pleasing tone.

4. Turn the colour control completely anti clock wise (to the minimum colour position). Turn the

brightness and contrast controls to obtain a picture of proper brightness and details.

5. Now tune in colour. Colour intensity of the picture depends on setting of this control. Carefully adjust

the colour control to obtain the desired amount of colour in the picture.

Note:

1. Skin tone of a person appearing on the screen provides a reference point for adjusting the colour.

2. Correct tuning is essential for receiving colour.

Result: Operating controls are operated and observed variations in picture when each control is

varied.


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TEEVISION SERVICING INSTRUCTIONS AND WARNINGS Safety Instructions

1. Remove the back cover of the TV receiver without hitting the neck of the picture tube 2. Connect the set to the mains power supply via an isolation transformer 3. Always wear chappals 4. Replace the safety components only by the components identical with the original ones 5. Wear goggles for the protection of eye

Maintenance instructions 1. Re solder the soldered portions through which the horizontal current flows such as pins of LOT,

fly back capacitor, Line output transistor, pins of connector joints to yoke coil etc. 2. Route the wire trees and EHT cables correctly 3. Check the strain relief of ac power chord for proper function to prevent the chord from touching

CRT, fusible resistor etc. Warnings

1. In order to prevent damage to ICs and transistors, avoid all high voltage flash over like EHT discharging, Mains filter discharging etc.

2. Be careful during the measurement in high voltage section 3. Never replace the modules or other components while the unit is turned ON. 4. When you align the set especially presets, use plastic rather than metals. It prevents short circuit. 5. Always use the lead free solder ( use tin solder only). This ensures that there will not be any dry

solder and that the soldered joints wont get heated up easily. Prefer the ratio 67:33 combination of tin and lead.

You can become a successful TV technician only if:

1. You know the basic theory and can understand circuit diagrams.

2. Which component is attached where on the printed circuit board, could be recognized by you on

looking at the PCB.

3. You could trace different wires in a TV and understand their functions

4. You could de solder and solder different components on PCB without damaging them or the PCB.

5. You could test and change easily the tuner, volume control etc. fixed on the panel.

6. You could use your multimeter easily in different ranges.

7. You have some necessary instruments and components.

8. You remember supply pin numbers of ICs and could trace dc supplies on PCB.

9. You could trace signal path on PCB.

10. You could recognize which part of the TV is faulty, by looking at the faulty picture and by listening the

defective sound.

11. You could detect faulty components by measuring resistances, volts and currents with a multimeter.

12. You have knowledge of necessary precautions to be observed during TV testing. You can get severe

shock or you can damage various components if you don’t take necessary precautions.


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13. You have good practice of setting AGC presets, horizontal hold, vertical section presets, linearity coil

etc. to get good picture and clear sound from Television

Correct use of Soldering Iron

1. Keep its bit clean by using a file.

2. Put solder on one side of bit only. Use the other side for heating purpose and for straightening

pins, wires etc.

3. Develop habit of holding soldering iron as a writing pen.

4. When de soldering joints, lift small bits of solder with the soldering iron and jerk them out of

the iron. Use de soldering wick for perfect de soldering.

5. When soldering a joint, first heat the joint for a few seconds as necessary, then apply solder

wire on the joint to be soldered.

6. Use good solder of 60% tin and 40% lead.

7. Clean the pins of new components with a blade and tin them before soldering.

8. Don’t use soldering iron on IC pins for a long time. Prolonged heating can damage the IC. Heat

the pin quickly with hot bit and apply solder wire.

Necessary Precautions in TV checking

1. Disconnect the TV from AC mains supply before touching any part inside the TV.

2. Discharge the DC filter capacitors of the main supply with the help of 100Ω/10W resistor and lead

wires or by using a test lamp. Else, you get severe shock.

3. It is important to discharge the picture tube before touching either of the EHT transformer, TV 20

or 18KV lead wire. You may get a severe shock due to electric charge accumulated at 18KV line.

For this, hold the thick plastic of a long screw driver, insert it in the rubber cap of EHT lead and use

another screw driver or lead wire to connect with the chassis ground. Never hold the picture tube

by its neck; it may break.

4. Arc testing of EHT should be done for a minimum time. Prolonged heating may damage BU 205.

5. Do not touch simultaneously the antenna wires and chassis of TV connected to mains supply. The

middle part of antenna dipoles id connected to a steel pipe fixed on a wall. If by chance, phase of

AC supply is coming on the chassis, then simultaneous holding of chassis and antenna wires can

give you severe shock.

6. Be very careful during soldering that drops of solder are not falling on the PCB and shorting the

tracks. The shorted tracks will produce many new faults in the TV being repaired.

7. Do not ever try to measure EHT voltage with an ordinary multimeter as it will immediately

become damaged.

8. If a TV in running condition develops some fault, its repair is easy as it has proper components

attached at proper places. If in case, a faulty TV is brought to you after getting serviced by others,

expertise is very much essential.

More points for a TV Technician

1. Chassis should be tested with a NEON tester, for AC supply phase not coming on it.


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2. If volume control and tuner become difficult to rotate due to dust, or give disturbance in sound

and picture, then clean them with white patrol or solvent oil.

3. TV to be repaired should be first tested with series lamp circuit. If it shows no short circuit, or none

of the part becomes very hot, then it should be connected to AC mains supply.

4. Sometimes after replacing the mains transformer of the TV, raster becomes weak and smaller,

although the voltage readings of transformer do not change. It happens when the replaced

transformer has thinner wires in its windings, i.e., it is of less power, and cannot deliver necessary

power.

5. Diodes like BY 127 and 1N 4007 appear to be alright when tested with a multimeter, but they still

does not work properly when used in a circuit. The 3 volts of dry battery of meter are incapable to

test such diodes, and should be tested by replacement when there is doubt.

6. Generally supply pin voltages of ICs and transistors decreases when they are short and increases

when they are open.

7. If during TV testing, some fault of TV appears to be rectified, when a probe of meter is touched

with some point of TV, it indicates that some resistance or capacitor is open at that point.

8. In case one diode of a bridge rectifier become open, it acts as a half wave rectifier, and output DC

voltage becomes low. Many defects appear to be present in TV due to this low DC supply.

9. When measuring DC voltage of some point, if needle of the meter tries to move in opposite

direction, interchange the probes to measure –ve DC voltage present in that point.

10. 12 pins are present in ICs TBA 810 and TDA 1044 and a thick metallic strip to be soldered between

heat sink and the PCB ground. Assuming pins 4, 5 and 12, 13 to be linked with the thick strip; these

ICs are sometimes taken to have 16 pins.

11. If there is too much distortion in picture and sound both, isolate these sections and check them

one by one. Open one end of 6.8 PF capacitor connected with pin 19 of CA 3068 to isolate the

sound section. Now repair the video section and try to get a good picture. Now disconnect one end

of the two capacitors bringing video signals to the base of BF 195. Reconnect 6.8 PF capacitor and

repair the sound section to get good sound.

12. Wave shapes at different points in a TV can be observed using a pattern generator and an

oscilloscope and faults of a TV can be detected very easily.


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CHARACTERISTICS OF SOUND

Human response

Threshold of hearing – 20 x 106 Pa

Average sound - 20 x 104 Pa

Threshold of pain - 63 N/m2

Woman’s speech - 220 to 2500 Hz

Men’s speech - 110 to 1000Hz

Telephone speech - 300 to 3400 HZ

Woofer reproduces sound frequencies of about 16 Hz to 500 Hz

Squawker reproduces sound frequencies of about 500 Hz to 5000Hz

Tweeter reproduces frequencies of about 5000Hz to 20 KHz


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Trouble Shooting Of TV Receiver Power supply section Identify the major components in this section

1. Heavy duty iron core power transformer 2. Fuses 3. Rectifier diodes 4. Filter capacitors

If “SET DEAD” symptom:

Cold Check

1. Check continuity and ohm across mains cord two pin plug – normal 30/50 ohms 2. Check ac and dc fuses for continuity 3. Ohms and continuity check for power transformer windings 4. Forward bias and reverse bias of power diodes 5. Ohms check between B+ points and chassis

Hot Check

1. Check ac voltage across primary winding 2. If normal, check ac voltages across the different secondary windings 3. If they are normal, check dc voltages at the junctions of the bridge rectifier 4. Check dc voltage at the dc fuse point

Probable faults

1. Defective ON/OFF switch 2. AC fuse open circuit 3. Open circuit or short circuit silicon diodes in bridge circuits 4. Shorted filter capacitors

Weak Picture, Weak sound Selective power diodes, defective power transformer Thick black bars on picture (Hum Bars) Open filter capacitors Upper/Lower half of raster blackened (Hum in video stage) Open filter capacitor in the video stage B+ line Picture wavering at sides of the raster Open circuit or leaky filter capacitors in the horizontal oscillator or horizontal amplifier stages. Intermittent picture/raster/sound

1. Loose/dry joints in pcb 2. Defective power diodes 3. Defective filter condensers


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4. AC/DC fuses defective TESTING AND TROUBLE SHOOTING IN THE VIDEO AMPLIFIER AND PICTURE TUBE Sections: Identify these sections on the PCB in the TV demonstrator, Familiarize with the major components in these sections: 1. Video amplifier transistor BD 115 with heat sink 2. Contrast control, 1 K 3. Collector load resistor, 3.9k, 10W 4. Beam current limiting diode OA 79 5. Brightness control, 500 K 6. Bleeder resistors for pin 3 and 4 of picture tube

Trace the B+ supply to this section: Ohms check B+ point to chassis Trace the input and output pin points in TBA 920 S To check this section for overall goodness: Inject a pattern generator signal at the base of BD 115 and look for bars on the screen Alternatively use a 1.5V battery cell. With its –ve connected to chassis, touch its +ve terminal at the base of BD 115 looking for a change in raster brightness. Checking contrast control: Connect a voltmeter between BD 115 and chassis. Note the voltage. Vary the contrast control and observe a variation of about 25/30 V - good. Checking brightness control: Connect a voltmeter to pin 2 of picture tube and chassis. Vary the brightness control from minimum to maximum, observing a variation of 30/35 V Checking the Picture tube and bias setting: Connect a voltmeter between pin 2 of the picture tube and pin 7 (pin 2 to –ve lead of the meter and +ve lead to pin 7 of the meter. Vary the brightness control and observe 20/25V variation. This indicates picture tube is good and its bias settings are okay.


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FAULTS REPAIR OF TEXLA TELEVISION Fault 1: Power line fuse blows when TV is switched ON The fault occurs when there is short in AC supply circuit of TV.

1. Open the plug and check whether the two wires are in contact. 2. Check the connections of ON/OFF switch. 3. Check the primary of mains transformer for short. 4. Check AC voltages at secondary of the transformer. 5. Disconnect rectifier circuit from the transformer. 6. Measure resistance of the windings and compare with the table given below.

Primary : 40 – 50 ohm Secondary (150V) : 40 ohm Secondary (15V) : 1 ohm Secondary (6.5V) : 0.5 ohm

7. Check if any of the 4 diodes of 150V bridge rectifier short 8. Check 4 diodes of 12 V bridge rectifier

Fault 2: DC Fuse blows when TV is switched ON

In case, first filter capacitor is short, DC supply gets connected directly with the chassis ground and fuse blows off.

Fault 3: Resistances of main DC supply become red hot

1. In case, second filter capacitor is short, heavy current will flow through in 160 ohm resistance, which will become red hot.

2. In case, BU 205 is short, 100 ohm resistor will become red hot. 3. Fuses will blow out if there is a short between supply line and ground anywhere on PCB. 4. 140V DC supply is also given to video output transistor, BD 115 and to the brightness control

circuit. If a short exists in these circuits, the value of DC supply may decrease, the resistances may become red hot, or a fuse may blow out. In case a fuse blows, it is necessary to find out the section where supply is short. For this detection, DC supply of a section is cut down and TV is switched ON. If the fuse still blows, short is not in this section. Similarly other sections are checked till the fuse stops blowing, and the faulty section is detected. Check the components of the section and detect the short. Supply to a section can be easily disconnected by cutting the PCB with a sharp blade. The cut can be easily soldered afterwards.

Fault 4: Violet sparking from LOT, TV 20 connectors or from EHT lead

All the above components come in 18KV circuit. If their insulating materials becomes weak or cracked, sparking starts due to the presence of very high voltages.

Araldyte can be used for temporary repair of cracked EHT. Defective EHT leads and connectors should be replaced. Loose connections should be made tight.

Caution: Discharge picture tube before touching EHT section.


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Fault 5: Blue flash and hissing sound comes from EHT some times

Fault occurs when corona discharge takes place in EHT section.

1. In case, solder joints of EHT lead are sharp, heat them with soldering iron and change them in smooth shape.

2. If dust or metal particles are present near final anode of a picture tube, they can short circuit the final anode and outer coating of the picture tube. Remove the particles if sparking takes place near the final anode.

Fault 6: No raster, sound okay

Possible faulty stages: Picture tube biasing section, absence of 18KV from LOT.

Whether EHT is working, can be detected by following two methods.

1. Bring a neon tester near the EHT transformer, but don’t touch it anywhere on LOT. If the tester starts glowing, it indicates that 18 KV pulses are present in EHT winding.

2. Measure 35V dc supply at cathode of the diode attached to pin 5 of EHT transformer. If this supply is available, LOT is working. For EHT formation, it is essential that,

1. 150 V dc supply should reach the collectors of BD 115 and BU 205 (Primary of LOT). 2. Presence of 15625 Hz pulses at the base of horizontal output transistor, BU 205.

The pulses produce negative volts on the base of BD 115. If multimeter gives a reading of -1.1V at the base, pulses are reaching the base of BD 115. If negative volts are not available, fault finding of IC CA 920 has to be done first. If EHT does not work even after dc voltage is available at collectors and negative volts are available on the base of BD115 and BU 205, EHT transformer or yoke could be defective.

Faults

1. Loss of Picture

Problem in the blocks particularly related to picture signals – i.e., Video detector, pre – amp,

video amplifier. May be because of defective transistor, open coupling capacitor, defective

diode detector, short or open in signal path due to parallel or serial components, improper

biasing etc

2. Dead Receiver ( No Raster, No sound)

Power supply, LOT (Horizontal output stage)

Different voltages to different sections are generated by LOT and any complaint to this

section can lead to “Dead Receiver”.

3. Dead Screen (No Raster, Sound Okay)

Problem with Picture tube biasing section


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a. Filament (Heater) voltage missing

b. Cathode voltage increased

c. Control grid voltage missing

d. Accelerating anode voltage missing

e. Focusing anode voltage missing

f. Weak Picture tube.

g. 15 KV from LOT does not reach picture tube

h. Incorrect setting of Picture tube controls

4. No Sound or sound distorted, Picture normal

a. 5.5 MHz trap

b. S. IF amplifier

c. FM detector

d. Audio Amp

e. Loud speaker

f. Volume control

5. Normal sound and raster, No picture

a. Video driver

b. Video output

c. Any problem in the signal path after the sound take off point

6. Horizontal line on screen

Vertical stage

a. Vertical oscillator not working

b. Defective V. deflection winding

c. Vertical transistor/IC complaint

d. Supply to this section may be missing

7. Vertical line on screen

a. Horizontal saw tooth pulses not reaching H. deflection windings

b. Defective H. deflection winding

c. Open coupling capacitor that couples saw tooth waveform from LOT to winding

d. Open linearity coil

8. Insufficient vertical height

a. Amplitude of V. saw tooth wave form less

b. Weak V. Oscillator

c. Weak V. Amplifier

d. Faulty output stage

e. Misadjusted height control

f. Shorted turns in V. deflection winding

9. Vertical Rolling

No synchronization


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a. V. Oscillator frequency too high or too low from 50 Hz

b. Defective sync separator

c. Defective integrator

d. Misadjusted V. hold control

10. Insufficient width of the raster

a. Amplitude of horizontal deflection wave form less

b. Weak H. Oscillator

c. Weak H. Amplifier

d. Shorted turns in H. deflection winding

11. Negative Picture

a. AGC circuit

b. Video detector

c. Picture tube circuit

12. Picture tearing apart (Loss of horizontal synchronization)

a. Horizontal oscillator output high or low than 15625 Hz

b. Sync separator

c. AFC

d. Differentiator

e. Absence of fly back pulses from LOT

13. Motor boating sound from Loud speaker

Audio section

Defective filter/ decoupling capacitor


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POWER SUPPLY COMPLAINTS

1. Dead Receiver

2. Insufficient width and height of raster

Caused due to fall in amplitudes of both horizontal and vertical saw tooth waveform.

a. Open filter capacitor

b. Open diode in bridge rectifier circuit

c. Excessive current drain at some point in the supply line

3. Dead Screen

4. Dim Raster

Due to low voltages on Picture tube screen grid and accelerating anode

5. Hum bars in raster, hum in sound

Defective filter/ decoupling capacitor

6. Weak Picture

Low dc voltage to RF and IF sections of receiver

7. Blooming of Picture

a. Leaky HV capacitor

b. Weak HV rectifier

c. Defective picture tube

d. High resistance in EHT lead due to defective series resistor

HORIZONTAL SWEEP CIRCUITS

1. Single vertical line on screen

2. Poor horizontal linearity

a. Defective linearity control

b. Incorrect drive voltage waveform

c. Defective output transistor/IC

d. Incorrect drive voltage amplitude

3. Horizontal fold over

(Severe firm of Non – Linearity)

a. Defective output transistor/IC

b. Faulty Oscillator or output circuit

c. Faulty biasing circuit of horizontal output stage

4. Horizontal Key stone effect

(Dim and narrow raster with its bottom wider than top or vice versa)

a. Defective horizontal yoke (shorted turns)

b. Shorted balancing capacitor across one set of the horizontal deflection coils.

5. Loss of horizontal sync


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VERTICAL SWEEP CIRCUIT

1. Horizontal line on screen

2. Insufficient picture height

3. Vertical rolling

4. Vertical key stoning

a. Shorted turns in vertical deflection coils

b. Defective vertical output stage

c. Defective thermistor across deflection coils

SYNC SEPERATOR AND PROCESSING CIRCUIT

1. Picture tearing apart and vertical rolling

Total synchronization problem.

a. Defective sync separator

b. Defective coupling capacitor to sync circuit

c. Faulty transistor/ IC used in the circuit

2. Vertical rolling

3. Picture tearing apart (Horizontal rolling)

4. Vertical Jitter (Picture jumps up or down)

a. Open capacitor in integrating circuit

b. Defective sync separator, incorrect biasing

c. Open by – pass capacitor

5. Horizontal pulling

a. Defective AFC diodes

b. Leaky sync coupling capacitor

c. Defective transistor/IC


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VIDEO AMPLIFIER CIRCUIT

1. No picture, sound and raster okay

Video amplifier section

a. Defective transistor/IC

b. Open contrast control

c. Open coupling capacitor

d. Open bias resistor

2. Loss of clarity on fine details

Poor high frequency response of Video Amplifier

3. Sound bars on Picture

a. Defective sound trap circuit

b. Misalignment of IF stages

4. Weak Picture

a. Weak transistor/IC in video Amp

b. Incorrect bias

c. Weak picture tube

d. Excessive AGC bias

5. Intermittent Picture

a. Defective video amp

b. Poor soldering at joints

c. Worn out brightness/contrast controls

VIDEO DETECTOR

1. No sound, No Picture, Raster okay

SOUND SECTION

1. No sound, Picture, raster okay

2. Weak or distorted sound

a. Faulty IC

b. Low S.IF amplifier gain

c. Improper alignment of S.IF

d. Improper alignment of FM discriminator

e. Defective loud speaker

AGC SECTION

1. Weak Picture

Due to excessive bias voltage to IF and RF amplifier stages

a. Incorrect adjustment of AGC control

b. Faulty AGC transistor/ IC

c. Shorted AGC filter

d. Keying circuit

2. Loss of sync


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If AGC is low, over loading may happen

3. Dark Picture and Buzz in sound

a. Defective AGC transistor

b. Leaky AGC filter capacitor

c. Low AGC on strong signals

4. Negative Picture

Reversed black and white picture caused by the reversal of polarity of video signal

a. Absence of CVS from Video Amplifier section to AGC circuit

b. Absence of fly back pulses from LOT

c. Faulty transistor/IC in AGC circuit

VIDEO IF SECTION

1. No picture and sound, Raster okay

a. IF amplifier section

b. Bad cable connections

c. Incorrect setting of AGC Preset control

d. Misaligned IF subsystem

2. Smeared Picture:

Due to excessive low frequency response

3. Ringing

Excessive high frequency response

4. Weak Picture

a. Low B+ supply

b. Weak transistor/IC

c. Incorrect AGC

d. Misaligned IF stages

TUNER SECTION

1. No Picture and sound, Raster Normal

a. No AGC voltage

b. No dc supply to tuner

2. Intermittent Picture

Tuner contacts not clean

3. Weak picture and sound, Raster normal

a. Weak/defective transistor

b. Incorrect AGC bias

c. Poor Antenna Connections

d. Open BALUN

4. Snow in Picture

Tuner not working, but VIF section working.. These unwanted signals appear as snow on

screen


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COLOUR TELEVISION RECEIVER

FONDA KIT

At present, the following TV companies use this kit. CROWN, TEXLA, BELTEK, WESTON, OSCAR, SUMTHIA, EYE LINE and other low cost television receivers.

Video IF and Sound IF section

In this kit, IC – CD 7680AP is used for VIF and SIF sections. IF signal from Tuner is given to IF pre – amp transistor, Q161 (C-1676). +12 V obtained from pin 7 of EHT is given to this section. IF signal is amplified in this section.

Amplified signal obtained from IF pre amp is given to SAW filter, Z 101 (38.9MHz). IF signal obtained at its output is given to pins 7 and 8 of IC CD7680 AP of VIF section.

After amplification, IF signals are given to video detector made in the IC where video signals are separated. This separated signal after amplification by the pre – amp comes out through pin 15. CVS and inter carrier sound are included in it. The crystal filter, Z601 (5.5MHz) separates sound signal and feeds it to pin 21 of the same IC. This sound signal is amplified and is given to FM detector made in the IC. In this section, carrier signal is separated and sound signal is obtained from pin 3.

Pin 1 of IC CD 7680AP is an input pin of volume control signal. Control signal from pin 39 of command IC is given to this pin through volume control transistor, Q 901 (BC 147).

RF AGC control voltage is obtained at pin 11 of this IC. This voltage is given to the AGC tapping of the tuner. AGC control is connected to pin 10 of this IC. AGC signal can be adjusted according to the requirement by this control. AFC control voltage is obtained at pin 13 of IC CD7680 AP and is given to AFC tapping of the tuner.

This IC works on +12 V supply which is obtained from pin 7 of EHT and is given to pin 20 of this IC.

Audio Amplifier Section

IC TDA 2611 and one transistor, Q 601 (A 1018 – pre – amplifier transistor) are used in the audio output section of Fonda kit. Audio signal from pin 3 of CD 7680 AP is first amplified by this transistor and feed it to pin 7 of IC TDA 7611 of audio output section. The amplified signals which come out through pin no. 2 of the IC is given to speaker and sound is heard.

Pin no.1 of TDA 7611 is supplied with +22 V obtained from the power supply. Pin 4 is the negative supply pin and is made ground.

Chroma Section

IC TDA 7698 AP is used in chroma section of FONDA kit. Colour composite video signal obtained from pin 15 of IC CA 7680 AP is fed to pin 39 of chroma IC through a parallel combination of ceramic filter, Z 201 (5.5MHz) and coil L 201. After amplification, this signal is detected by the same IC. After detection, Y – signal goes to Y amp section made internally in this IC and remaining colour and sync signal is made out


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from pin 40 and given to pin 5 of this IC. Pin no. 5 is the input pin of chroma band pass amplifier. The signal is amplified and then taken out from pin 8 and fed to chroma trap (X 502). In addition to that, signal from pin 8 is also given to pin no. 17 (pin of AFC section). Pin 41 is the contrast control pin. Contrast control signal obtained from pin 37 of the command IC is given to this pin. Pin 4 is the brightness control pin. Brightness control signal is fed to this pin from pin 38 of system control IC. Pin 7 is the color control pin. Colour control signal from pin 36 of system control IC is fed to this pin.

Green colour signal, (G-Y) obtained from pin 20 is given to the base of green colour amplifier transistor, red colour signal (R-Y) from pin 21 is given to red colour amplifier transistor and (B-Y) signal output from pin 22 is fed to blue colour amplifier transistor. Y signal obtained from pin 42 of IC TA 7698 AP is given to pin 3 of this IC through a Y delay line. Luminance signal (Y signal) is made out from pin 23 of the IC and is given to luminance amplifier transistor, Q 202 (BC 157). This transistor amplifies Y signal and feeds this to all the three colour output transistors.

Horizontal and vertical oscillator sections are also located in IC TA7698AP. Horizontal oscillator signal is made out from pin 32 of this IC and reaches in horizontal driver section. In addition to this, vertical signal is made out from pin 24 of this IC and reaches in vertical section. Horizontal and vertical sync signals along with CVS are available at pin 39 for synchronizing frequency of horizontal and vertical oscillators. In this way, TA 7698AP works as both chroma section and vertical and horizontal oscillator sections.

CRT drive section

Three transistors, Q 507, Q 508 and Q 509 (all C 2482) are used in this section – each for amplifying (R-Y), (G-Y) and (B-Y) signals respectively. A transistor, Q 202 (BC 157) amplifies the Y signal obtained from pin 23 of chroma IC. Y signal obtained from this section is given to blue colour output section through B-drive, to green output section through G drive and given direct to Red colour output section (Y signal is applied to emitter of transistors used). +85V supply is obtained at these three colour output sections from pin 2 of EHT.

Colour difference signals (R-Y), (B-Y) and (G-Y) obtained from chroma IC are amplified in these three colour output sections and are mixed with Y signal which is fed to the emitters of these transistors to produce R, G and B. these colors are then fed to the respective cathodes of CRT. Colour cut controls of red, green and blue signals are connected in the signal path between chroma IC and colour output transistors. White balancing is adjusted at CRT by these drive and cut controls.

Vertical output section

Three transistors are used in vertical output section of FONDA kit. Transistor, Q 303 (C 2229) is connected in vertical driver section. Transistors, Q 306 (D381) and Q 307 (A 940) works as push pull amplifier in output section. Vertical signal of 50Hz generated in CD 7698AP is available at pin 24 and both driver and amplifier output sections amplifies this signal and finally this signal is given to vertical yoke coil.

Horizontal output section:

Two transistors serially Q 402 (2SC 2482) and Q 404 (2SD 1427) are used in this section. Transistor, Q 402 works as a horizontal driver and transistor, Q 404 works as a horizontal output transistor.


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Line signal of 15625Hz obtained from pin 32 of CD 7698 AP first reaches in horizontal driver section. Line signal after amplification reaches horizontal output section through LDT (line driver transformer). Line output transistor, Q 404 works as an electronic switch. It is turned ON and OFF according to line frequency. +110V supply is given to horizontal output section from power supply section through primary winding 1-2-3 of EHT transformer. Based on Faradays law of electromagnetic induction, LOT develops a voltage of 20 KV at its secondary.

System Control Section

When remote control is used with any TV kit, then all functions of that TV are controlled by system control section. This section is made on main PCB of Television.

IC ST MB23A9950F is used in system control section of Fonda Colour TV. All sections of TV are controlled by this IC. In this system control IC, analog output section is made for controlling voltage synthesizer, tuning, On screen display (OSD), character generator, remote control, decoder, contrast, brightness, colour and sound.

Audio/Video Section (A/V IN)

Audio – IN and Video – IN circuits are connected for observing and listening program by giving signals of audio and video from VCD/DVD in FONDA kit. A/V out sockets are provided in most of video CD/DVD players for obtaining output audio/video signals. Audio/video signals obtained from these sockets are given to A/V in socket of television. If A/V facility is not available in any TV, then convertor is used for converting these audio/video signals into RF signal.

Power supply Section

Switch mode power supply is made in Fonda kit by using four transistors. Transistor Q801 (C1815) output adjuster, transistor Q 802 (C369) power oscillator, transistor Q803 (C1815) power amplifier and transistor Q804 (BU 508A) is used as main switching transistor. SM transformer of 5 separate windings is used in this kit. Two supplies serially +110V and +22V are obtained from output of this power supply. When main power ON/OFF switch is turned ON, then +22V starts producing. This supply is given to IC LM7805 of sound output section and relay. When power ON command is obtained by remote control or panel key, then relay will turn ON and 110V supply will be obtained. +33V supply is made by this +110V supply, this supply is given at VT tapping of tuner.


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FAULTS IN SMPS

Usually a voltage dependent resistor commonly known as MOV (metal oxide varistor) is used between the mains ac terminals to bypass variations of ac supply voltage.

Typical circuit of SMPS used in Philips television


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FAULTS IN SMPS Aim: Identify the stages in SMPS, faults in SMPS and rectification procedure. Equipment Required: An SMPS circuit, 100Walts bulb, Multimeter, Tool Kit box. Theory: In SMPS circuit the general faults occurring in the circuit as follows. 1) Burning of fuse 2) Failure of switching transistor. 3) No 110V dc output 4) Output dc supply less than 110V. 5) The output dc. Supply more than 110V. Procedure (Connect a 100W bulb to the circuit and measure voltages) 1. Burning of fuse: When the problem IS in the switching converting transistor, bridge rectifier and filtering capacitor, the fuse burns even if it is replaced new one. 2. Failure of switching converting transistor: In SMPS circuit, if any transistor is shorted, identify the same and replace it in the place. Check the all transistors, base, collector, emitter resistors and diodes in the circuit. 3. No. 110V. dc output : Check the mains power chord, bridge rectifier, switching convertor transistor, switching convertor. Transistor collector presents 325V dc. Base voltage will be 2V dc or less than 2V. Also check proper grounding of emitter. Check the supply voltage. If there is no 110V dc, check error amplifier transistor, preset driver etc. 4. Below 110V. dc : If the fault in error amplifier transistor, check base, collector and emitter and components connected. If any one of the above component is shorted, 110V dc goes down. Also check the base feed back network. 5. Above 110V dc : If the fault in error amplifier transistor base, collector and emitter any one of the components are leakage or open. Result: Problems in SMPS and rectification procedure are studied.


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POWER SUPPLY SECTION OF FONDA KIT


141

POWER SUPPLY SECTION OF FONDA KIT

Description of the Circuit

Two supplies are made out at output of power supply of Fonda Kit - +110V and +22V. AC in reaches at input of line filter L210 through ON/OFF switch and AC fuse, F210. This supply is given to degaussing coil from output of line filter 210 through PTC thermistor. In addition of degaussing coil, this supply is fed to bridge rectifier diodes. Capacitors connected in parallel of each diode are surge voltage safety capacitors which provide safety to diodes from supply coming by jerk.

The dc supply from bridge rectifier is filtered by filter capacitor, C811. Negative dc voltage from negative tapping of bridge rectifier is made earth through resistance R805. This earth is called floating negative. Total four transistors are connected in this power supply. Transistor Q801 is a output voltage adjuster transistor. Transistor Q802 is a power oscillator transistor.Q803 is a power amplifier transistor. Q804 is the power output transistor. Positive supply from the bridge rectifier is given to the collector of this transistor through winding 1 & 5 of SM transformer and its emitter is connected with floating negative through resistor, R816. When power is turned ON, then at first this transistor turns ON by obtaining voltage from resistance R803 and R804 connected at base of transistor. Current flows in winding 5-1 of SM transformer by it and voltage produces in other windings too. Voltage obtained from tapping 8 of SM transformer is rectified by diode D805A and reaches at emitter of Q802 through diode D804. Negative supply is given to the collector of this transistor through R825.starting pulse is obtained at base of this transistor through R811 and C 804. This transistor starts oscillations by it, signal is made out from its collector and reaches at base of Q803. This transistor amplifies this signal and feeds it to the base of Q804. This transistor makes switching at fixed rate by this signal. Intermittent current flows in the winding 5-1 of SM transformer. Current pulses of fix frequency are produced in this winding of SM transformer. SM transformer works on these pulses and voltage is produced in its all other windings.

In this circuit, voltage is obtained from winding 9-10 for output voltage adjuster circuit. This voltage is rectified by diode D803 and filtered by capacitor C806. Positive supply is given to collector of Q801 through R821 and fix voltag3 is given to emitter through network made by resistance R820 and zener diode, D801. Any change made at the base of this transistor makes change at base of Q802 through R823. Variation is made in oscillation of transistor by it and switching rate of switching transistor effected by it, value of output supply changes by it. In this way, the value of supply can be adjusted according to requirement by preset connected at base of Q801.

Pin 4 of SM transformer is connected to chassis ground. Supply obtained between pin 4 and 2 winding of SM transformer is rectified by D810. C810 connected in parallel to this diode is a surge voltage safety capacitor. +22V obtained at the output of this diode is given to following sections of circuit

1. To pin 1 of IC TDA 2611 through R601 used in sound output section 2. To pin 1 of regulator IC 7805 through R980 3. To one tapping of 12V relay connected in power supply through R610

This supply does not turn OFF by pressing power button of remote hand set. Voltage produced in the winding connected from pin no. 3 and 4 of SM transformer given at N/O tapping of relay through R610A and R610B when is turned ON by remote hand set. Then relay begins working, pole of relay connects with O/C winding by it and voltage is made out from pole. This voltage is rectified by D802 and filtered by filter


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capacitor, C810A. in this way, 110V is obtained at the output of D802. Pole of relay connects with O/C tapping in that condition when supply is given to relay coil. This supply is obtained at relay from panel key board or by giving power on command by remote handset. +110V reaches the following sections of the circuit

a) +33V is obtained from +110V supply through resistance RA902 and zener diode DA13 which is filtered by CA904. This 33V is given at TU terminal of tuner through regulator circuit.

b) This supply is given to primary coil of line drive transformer and collector of line driver transistor, Q402.

c) +110V supply is given at pin 3 of EHT through R244. This supply is made out from pin1 and given to collector of horizontal transistor Q404.

d) This supply is given at one tapping of horizontal hold control, R451 through R414. Supply from this line is also given to base of line driver transistor Q402.

e) Horizontal oscillator section operates on this +110V supply before getting +12V supply from pin 7 of EHT. This supply is given to pin 33 of IC TA 7698 through R416.

Result

Studied about the power supply section of FONDA kit


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ELECTRONIC TUNER


144

Observation

Programme Tuner Pins Voltage Programme Tuner Pins Voltage

DD NATIONAL

BU DD NEWS

BU

VT VT

BH BH

AGC AGC

BL BL

AFC AFC

B+ B+

IF IF


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ELECTRONIC TUNER

Aim: To study about television Tuner and to measure tuner voltages when the receiver is set to receive programmes of DD National and DD News. Theory An electronic tuner is commonly used in Television Receiver to tune different stations. A varactor diode is employed in this tuner for tuning purpose. Generally 4 sections of the television receiver are tuned at a time – Antenna Circuit, RF Amplifier, Local Oscillator and Mixer. Electronic tuner commonly has 8 leads in addition to earth and RF – in.

1. BU :- UHF band. Voltage of about 6V comes to this pin only when the receiver starts scanning for programmes in UHF Band.

2. VT:- Tuning Voltage. Voltage varies from 0 to 30V. While tuning each band, voltage gets varied in this pin

3. BH: - VHF (High) band. Signals of Band III (channels 5 to 12) are received in this band. Frequency range of this band is from 174MHz to 230 MHz.

4. AGC: Automatic gain control. Delayed AGC produced by Video IF amplifier is applied to this pin. More AGC voltage to this pin can produce ghost images and less voltage can produce “GRAINS”

5. BL:- VHF (Low) band. Signals of band I (Channels 2 to 4) are received in this band. Frequency range of this band is from 41 MHz to 68MHz.

6. AFT: Automatic frequency Control. If the Video IF frequency shifts from 38.9MHz, a control signal is produced and applied to this pin (across varactor diode). This voltage corrects the local oscillator frequency.

7. B+:- Supply to tuner (12V) is applied to this pin. 8. IF : Output from tuner is obtained at this pin. In colour television, there are three IF frequencies –

Picture IF of 38.9 MHz, Sound IF of 33.4 MHz and Colour IF of 34.47MHz. 9. Shield: The tuner is enclosed in a metallic shield. The shield is connected to earth. 10. RF – in: Output from the antenna is applied to this pin. The voltage is directly fed to the RF

amplifier section. Procedure:

1. Remove the back cover of the CTV receiver and take the main board out from the cabinet. 2. Switch on the receiver and measure the voltages at the terminals of the tuner and note them. 3. Connect the antenna and tune the receiver to different stations. 4. At each programme, take the voltages at different terminals of tuner. 5. Now set the TV into automatic tuning option and see how the voltage variation occurs at BU, BH,

BL and VT. 6. There will be voltage at BU terminal only if the receiver starts tuning in UHF Band. Similarly,

voltages can be seen at BH and BL when band shifts to BH and BL respectively. 7. Tuning voltage, VT changes from 0 to 30V when tuning of stations in each band take place.

Result: Studied the working of tuner. Observed and measured the terminal voltage of tuner when it is set to receive signals of DD National and DD News Programmes.


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TUNER SECTION OF FONDA KIT


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TUNER SECTION OF FONDA KIT

Circuit Working

Total 5 transistors are used in the tuner section of FONDA kit. Among these, QA02, QA03 and QA04 are serially UHF, VH and VL band selection transistors. Transistor Q903 is a tuning voltage controller transistor and Q910A is a AFT buffer transistor.

VL band switching voltage (negative) is made out from pin 1 of system control IC and reaches at base of VL band switching transistor, QA02 through R915. This transistor turns on by it and positive voltage obtained at collector reaches at tapping of electronic tuner. +12V supply is given at this tapping. Channels of VL band can be selected by obtaining supply to this tapping.

At the time of auto tuning, first of all VL band programs are tuned. When this tuning is completed, next band (VHF 3) is selected. In this position, band switching negative voltage is made out from pin2 of system control IC. After this, BU voltage also reaches tuner in the same fashion

In this way, pins 1,2 and 3 of system control IC and transistor QA02, QA03 and QA04 combine work for band selection in electronic tuner.

Transistor Q903 is used for supplying essential tuning voltage at VT tapping of tuner. +33V supply is given at its collector and emitter is made direct ground. This +33V supply is obtained from +110V of power supply through resistance RA902 and zener diode DA13Z33V. Tuning control voltage is obtained at base of transistor Q903 from pin 33 of system control IC through resistor, R909. This voltage varies from 0V to 5V, these vary while making tuning by remote or panel board. When this voltage reaches at base of transistor Q903, then this transistor turns ON and its collector voltage drops by it. In this way, voltage of collector will drop on the basis of voltage obtained at base, which reaches the VT tapping of the tuner. 0.7 to 33V supply is given at this tapping. AFT tapping of electronic tuner is used for automatic fine tuning. AFT signal obtained from pin 13 of IC 7680 is given at this tapping. AFT signal is helpful in locking signal.

MB tapping of tuner is positive supply (+12V) tapping of mixer section made in the tuner.

After obtaining all supplies, IF signal is made out from IF tapping and this signal is fed to VIF pre amplifier transistor Q161.

Result

Studied the working of Tuner section of Fonda Kit


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System Control Section of Fonda Colour TV Kit


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SYSTEM CONTROL SECTION OF FONDA COLOUR TV KIT

IC ST MB23A9950F is used in system control section of FONDA kit. This is CMOS IC of total 40 pins; its pins are dual in line.

Pins Function Voltage measured

1 UHF band switching signal out

2 VH band switching signal out

3 VL band switching signal out

4 TV/AV switching out

5,6,7,21,22 Key

8 & 9 OSD oscillator

10 N/C

11&12 Memory IN/OUT

13 Horizontal blanking input

14 Vertical blanking input

15 AFT input

16, 19 &20 Ground

17,18,23 Bias

24 Reset input

25&26 VCO pins

27 Identify input

28 Standby output

29 Y OSD output

30 Green OSD output

31 Red OSD output

32 N/C

33 Tuning signal output

34 Remote input

35 N/C

36 Colour control signal output

37 Contrast signal output

38 Brightness control signal output

39 Volume control signal output

40 Positive supply pin


150

VIDEO IF AND SOUND IF SECTION


151

VIDEO IF AND SOUND IF SECTION

Aim

To study about the Video IF and sound IF IC, CD 7680 AP used in Fonda receiver and to take the biasing

voltages of the IC.

Theory

IC CD7680AP is a 24 pin dual in line IC which is used for VIF and SIF sections in Fonda kit. The IC consists of

following sections.

1. VIF amplifier section 2. Video Detector section 3. Video amplifier section 4. AGC section 5. AFT section 6. SIF amplifier section 7. FM detector section 8. DC volume control 9. Audio pre amplifier

Working IF signal obtained from IF tapping of the tuner first reaches the base if pre amp transistor, Q161

through a capacitor, C161. +12V supply obtained from pin 7 of EHT is given to its collector as

shown. The transistor amplifies IF signal obtained at its base and this amplified signal is given to

SAW filter through capacitor, C163.

Signal from this filter is applied to pins 7 and 8 of the IC (pins of video IF). After amplification,

video signals are given to video detector circuit. Here, video signals are detected and given to

video amplifier section. Output of video amplifier which includes both CCVS and 5.5 MHz sound

inter carrier frequency is obtained at pin 15. The ceramic filter, Z 601 detects this 5.5 MHz and

gives it to pin 21 (input of sound IF amplifier. The audio signal from FM detector section (located

in the IC) comes out through pin 3 of the IC. This signal is amplified and given to loud speaker.

FM detector coil and circuits is made at pin 22 and 24 of the IC. Volume control signal obtained

from pin 39 of system control IC is given to pin 1 of this IC through transistor, Q901.


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Pins Function Voltage Measured

1 Input for attenuator

2 Noise filter

3 Audio signal output

4 Ground

5 AGC detector

6 Feed back out

7 & 8 IF input

9 Feed back IN

10 AGC control

11 RF AGC output

12 Ground

13 & 14 AFT out

15 Video Out

16 AFT detector

17&18 Video detector

19 AFT detector

20 Positive supply, +12V

21 SIF IN

22&24 FM detector

23 FM controller


153

Pins 17 and 18 are pins of video detector section. The detector coil, L507 makes a tuned circuit of

resistance R108 and coil and a capacitor connected internally in parallel which detects the video.

After that, the signal reaches AFT section. The signal is detected in AFT section and obtained at pin

13 which is further sent to AFT tapping of the tuner. In order to lock channel with this signal, the

signal is fed to pin 15 of system control IC through AFT buffer transistor, Q 910 A.

AGC voltage from pin 11 of the IC can be controlled by AGC control (15K) connected to pin 10 of it.

Result

Studied about the IC

Took the pin voltages of the IC.


154

SOUND OUTPUT SECTION


155

SOUND OUTPUT STAGE

Aim:

To study about the sound output stage of FONDA kit.

To measure the pin voltages of the IC, TDA 2611A

Theory

IC TDA 2611A is used in sound output section. It is a 9 pin single in line package IC.

Pins Function Voltage Measured

1 Positive supply

2 Output

3&5 N/C

4 Negative Supply to audio output

6 Negative supply to audio driver

7 Signal input

8 Filter

9 N/C

Audio signals from pin 3 of 7680 is amplified by audio amplifier transistor, Q 601 which is a PNP

transistor. Positive supply is given to its emitter. The amplified signal is then fed to pin 7 of audio out put

IC, TDA 2611. This IC amplifies audio signals to the sufficient level and is taken out from pin 2 and fed to

loud speaker. Positive supply either from pin 2 of SM transformer or from pin 7 of LOT is fed to pin 1 of

this IC.

When ‘MUTE’ button is pressed by remote control, the low voltage from pin 39 of system control IC

reaches the volume control transistor, Q901. This transistor turns OFF by it and the increased collector

voltage reaches pin 1 of IC 7680. When high voltage comes at pin 1, then no audio signal comes out from

pin 3.

Result

Studied about the sound output section.

Measured pin voltages of the IC.


156

COLOUR SECTION


157

COLOUR SECTION

Aim

To study about the colour section of FONDA kit. To measure pin voltages of the colour ICTA7698AP Theory IC TA7698AP is used in colour video section of Fonda kit. This is a 42 pin dual in line package IC. It consists of Chroma Amplifier, Band pass amplifier, R-G-B matrix, Luminance signal amplifier and colour sub carrier oscillator. Horizontal and vertical oscillators are made in this IC because maximum pins of this IC are used for colour video section, hence it is called colour IC. The pins 1 to 23 and pins 38 to 42 is used for colour video section. Working Composite colour video signals obtained from pin 15 of IC TA 7680A is given to pin 39 of TA7680AP through coil L105, R598, L201 and ceramic filter Z201. Composite colour video signal is given to inverter circuit made internally in this IC through this pin. This section detects signal in addition to amplification. Y signal obtained from this section goes in internally made Y amplifier section. The composite signal obtained from pin 40 of this IC are given to pin 5 which is the input pin of chroma amplifier. The amplified chroma signal comes out from pin 19 through chroma trap circuit. In addition to this, chroma signal from pin 18 is also given to pin 17 of AFC section. Y signal is made out from pin 2 of this IC and given to pin 3 through delay line, W201 and capacitor, C204. Contrast control signal from pin 37 of command IC is fed to pin 41. This signal controls Y signal and makes contrast of picture. It can be adjusted by remote control through contrast key. Brightness control signal from pin 38 of system control IC is given at pin 4. This signal controls the brightness of the picture. Colour control signal from pin 36 of system IC is given to pin 7 of this IC. G-Y signal from pin 20, R-Y signal from pin 21 and B-Y signal from pin 22 ate given to concerned colour video output sections connected on CRT drive board. Y signal is made out from pin 23 of IC and given at base of Y signal amplifier transistor. The signal is amplified by this transistor and given to emitter circuits of all three colour output transistors. Horizontal blanking pulses are given through resistance R217 and diode , D203 and vertical blanking pulse3s are given through D 202 at base of this transistor. Result Studied about the colour section of FONDA kit. Measured pin voltages of the colour IC, TA 7698AP.


158

Pins Function Voltage measured

1 Video signal amplifier pin

2 +ve supply pin of colour video section and oscillator

3 B&W video signal input which reaches from pin 42 via delay

4 Brightness up/ down signal input pin

5 Input pin of CCVS

6 Automatic colour control input pin

7 Colour up – down signal input pin

8 Output pin of chroma amplifier section.

9 Colour sharpness control pin

10 Phase of colour signal is controlled by this pin

11 Negative supply pin of colour video section. Ground

12 Pin of colour killer section

13, 14, 15 Pins of colour sub carrier oscillator

16, 18 Pins of colour AFC section

17 Colour sync signal given to this pin from pin 8

19 Pin of colour mixer section

20 (G-Y) output

21 (R-Y) output

22 (B-Y) output

23 Y signal output

36 PAL switch ON pin, Horiz. Blank pulses from LOT given to this.

39 Composite video sync signal input

40 Amplified CCVS come out through this pin

41 Input pin of contrast control up/down signal

42 Output pin of Y signal. Its output fed to pin 3 through delay


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160

RGB & OSD DRIVE SECTION (CRT DRIVE BOARD)


161

RGB & OSD DRIVE SECTION (CRT DRIVE BOARD)

Aim: To Study about RGB and OSD drive section

Total five transistors are used in CRT drive board of Fonda Kit. Among these, transistor T1 (2SC1815) is

green colour ON screen display out and transistor T2(2SC1815) is red colour ON Screen display output

transistor. Transistor Q507(C2482) is red colour output, transistor Q508 (C2482) is green colour output

transistor and transistor Q509(C2482) is the blue colour output transistor. Red colour signal obtained

from pin 21 of chroma IC TA7698AP is given to base of red colour output transistor Q507(C2482) through

resistance R527(560 ohm). This is an NPN transistor. +185V supply obtained from pin 2 of EHT is given to

its collector through resistance R591(15K,2W). Red colour signal amplified by this transistor is given to

red cathode (pin 8) of CRT. Green colour signal obtained from pin 20 of IC TA7698AP is amplified by the

transistor, Q508 is given to pin 6 of CRT through R902. In the same way, blue signal obtained from pin 22

is amplified by Q509 is given to blue cathode pin (pin11) of CRT through resistance R903. In this way

green, red and blue signals obtained from pins 20, 21 and 22 are given to base of concerned output

transistors, amplified and made out from collector and given to concerned pins of CRT.

Three presets (10K) for red cut off, green cut off and blue cut off are provided. Negative supply to

emitters are given through these presets. In addition to that, VR253 and VR252 (200 ohm) connected in

emitter circuits of green output transistor and blue output transistor are called green drive and blue

drive. Amplification of these transistors is adjusted by these both drive controls and three cut off

controls.Y signal obtained from Y signal amplifier is given to emitters of all three colour output

transistors.

In this way, transistor Q507, Q508 and Q509 connected at CRT board work for bringing color picture on

screen. Other two transistors on the board work for ON screen display. Red OSD signal from pin 31 of

command IC is given to the base of Q905 through 1K. +12V is given to its collector through 680 Ohm.

Negative supply given to its collector through R957. Amplified signal is obtained at its emitter reaches the

base of red OSD output transistor, T2(2SC1815) through 10K and resistance R2 and 220pF capacitor are

connected in parallel. This signal is amplified by transistor and reaches the emitter of colour output

transistor 507 (C2482) through R4(220 ohm). In this way, this signal along with colour video signal

reaches at cathode of CRT.

Green OSD signal from pin 30 reaches the base of Q506 through 1K. This transistor amplifies this signal

reaches T1(2SC1815) through R5 and C928 and resistance 10 ohm connected in parallel. This signal is

amplified by this transistor reaches the emitter of Q508 through R6. In this way, signal along with green

colour video signal reaches the green cathode of CRT and green display is obtained on screen.

Result: Studied about RGB and OSD driver section of Fonda Kit.


162

FAULT ANALYSIS – COLOUR TELEVISION

Aim:

Complete the chart after identifying the relation ship between the facts depicted in the few examples

shown below.

Stage Function Raster

Picture

Sound

colour

Tuner Selection of channels, conversion of Picture and Sound Carriers to Ifs of 38.9 MHz and 33.4 MHz

OK X X X

AFT Does fine tuning adjustments automatically, Essential in colour receivers as this is a critical adjustment

OK OK OK X

Remote Tuning

Helps to tune, controls volume, contrast etc from a distance OK X X X

Video IF and Detector

This section provides necessary selectivity and does vestigial side band correction, minimizes adjacent and co-channel interferences

OK X X X

Sound S.IF amplifier amplifies 5.5 MHz sound, S. Detector converts S.IF into audio frequency signals, Audio output stage raises the power level of the audio signals

OK OK X OK

Volume Control

Located in audio amplifier stage and controls the audio signal level

Brightness Control

Adjusts the overall light output of the picture tube

Delay line (Not stage)

Delays the Y signal so that it arrives at the picture tube at the same time as the colour signal information

Video Output Amplifier

Provides additional amplification to video signals up to about 90 to 150 Vpp. This signal drives the picture tube

AGC Sync Seperates sync from CVS, Generates dc voltage proportional to the strength of input RF signal

Vertical output stage

Multivibrator in this section generates vertical saw tooth and output stage drives vertical deflection yoke

Height control

Adjusts the amplitude of vertical sawtooth waveform

Vertical Linearity

Adjusts the linearity of vertical saw tooth

Horizontal AFC and Oscillator

AFC compares horizontal sync pulses with horizontal oscillator output and generates a dc voltage that depends upon any frequency error in between them. This error voltage corrects the error. Horizontal oscillator produces saw tooth wave form of 15625 Hz

Horizontal Hold Control

Controls the frequency of Horizontal Deflection oscillator


163

Horizontal Output

It drives the deflection yoke to provide horizontal scanning. It supplies pulses for AGC, AFC , blanking and provides ac voltages needed for high voltage second anode and focusing electrodes of picture tube

Damper Damper is primarily responsible for deflection on the left hand side of the raster. This also generates the B+ boost voltage

High voltage rectifier

Rectifies the output of LOT to produce 15 to 21 KV of dc. TV 20 diode commonly used.

Focus Control

Controls the dc voltage output to focus control, thus adjusting the focus

Convergence

The circuit does not emply any transistors. These circuits take a sample of the horizontal and vertical deflection voltages and combine them to form the correction voltages and currents

OK Poor convergence

OK OK

Chroma Band Pass Amplifier

Amplifies and separates the high frequency chrominance signal from the CCVS

Colour Control

Determines the output amplitude of the chroma band pass amplifier. Adjusts the colour saturation of the colour picture

Colour Killer

Acts like a switch to turn ON or OFF the band pass amplifier. The switch turns ON the BPA when colour signal is transmitted and turns it OFF during monochrome receptuion

Burst Amplifier

Switch that is keyed ON and OFF by a pulse coming from the horizontal output amplifier. Burst gate is turned ON during the time that the colour burst appears at its input. The only output of the stage is 8 to 11 cycles of colour burst. During black and white reception, no burst

APC Compares the colour burst coming from burst gate with 4.43 MHz generated by sub carrier oscillator. If any phase or frequency error observed between these signal, a dc error voltage is generated and it forces the oscillator into synchronism with the colour burst

Chroma Oscillator control

This stage fed by dc output of phase detector. Depending upon the magnitude and polarity of this dc voltage, thisw stage forces the chroma oscillator to synchronise with colour burst

OK OK OK

U and V demodulator

Demodulate high frequency chrominance signal colour difference low frequency video

G-Y, B-Y and R-Y Amplifiers

Converts U and V demodulator outputs into R-Y, B-Y and G-Y signals. Also amplifies these signals and feed them to picture tube

Red, Green and Blue drive control

To obtain proper grey scale tracking


164

NECK CONFIGURATION OF COLOUR PICTURE TUBE


165

NECK CONFIGURATION OF COLOUR PICTURE TUBE

Aim To study about the neck configuration of picture tube. To measure neck voltages at the base socket of picture tube Theory Unlike monochrome picture tube, colour television picture tube has three electron guns each for

green, blue and red colours. Sony television employs TRINITRON picture tube, where as all other

television receivers employ PIL (Precision In Line) picture tubes. Yoke is placed at the neck. In addition, a

degaussing coil is wounded around the picture tube to demagnetize the effect of earth’s magnetic field.

There are two types of picture tube based on the Neck configuration – Broad neck and Narrow

neck. The voltages at the neck of a broad neck picture tube are as follows.

SL. NO PINS TYPICAL VOLTAGES

VOLTAGE MEASURED

1 FOCUS 1 5KV Cannot be measured

2 FREE/ EARTH 4 0V

3 G1 (CONTROL GRID) - EARTH 5 0V

4 GREEN CATHODE 6 200V

5 G2 – SCREEN VOLTAGE 7 300 TO 450V

6 RED CATHODE 8 200V

7 FILAMENT 9 &10 6.3V (AC)

8 BLUE CATHODE 11 200V

9 FREE OR EARTH 12 0V

RESULT

Studied the colour picture tube connections

Measured the neck voltages at the base pin socket of the picture tube.


166

COLOUR RECIEVER SYMPTOMS

Symptom: Screen with over blue and Retrace. Possible Faulty Section –Blue output section. Blue cathode voltage may be decreased. 1: Collector resistance value high. 2: blue transistor may be short. 3: IC output may be increased. Symptom: Blue absent screen (Yellowish Screen) Possible Faulty Section:-Blue output Section. Blue Cathode Voltage may be increased. 1. Blue transistors base to emitter junction not to be forward biased. 2 Blue output transistor may be open. 3. Blue IC output may be missing. 4. Blue cathode may be weak. Symptom: DEAD RECEIVER. Possible Faulty Section 1. Power supply 2. Horizontal output 3. Horizontal oscillator Symptom: Red colour absent (Only Cyan) Possible Faulty Section

Red cathode output section.

1. Red cathode voltage may be increased. 2. Red output transistor may be open. 3. Red IC output may be missing. 4. Red cathode may be weak. 5. Red output transistor base to emitter junction may not to be forward biased.

Symptom: OVER RED AND RETRACE LINE Possible Faulty Section : Red output section. 1 .Red cathode voltage may be decreased.

2 collector resistance value may be high.

3 IC red output may be missing

Symptom: DEAD SCREEN Possible tally stages; 1. Filament Voltage may be missing. 2. G2 voltage may be decrease.


167

3. 3-cathode voltage may be increase. 4. Final anode voltage may be miss. 5. Picture tube may weak. Symptom: OVER BLUE RETRACE LINES Possible faulty stage;

Blue output section:

1. Blue cathode voltage may be decreased

2. Collector resistor value may high

3. IC is ok may increased

4. Blue output transistor may short.

Symptom: DEAD RECEIVER WITH SHORTING SOUND Possible tally stages; Horizontal output section Horizontal oscillation section Power supply section Check power supply LPS and HPS Shorting component, check weather it’s direct or indirect Collector capacitor was shorted. Symptom: SCREEN WITH OVER BRIGHTNES AND RETRACE LINES Possible faulty stage

1. G2 voltage may be increased 2. 3-cathode voltage may be decreased

3. Picture tube may short

4. G1 may not be grounded

SYMPTOM: OVER BRIGHTNESS & RETRACE LINE

Possible faulty stage;

Picture tube biasing section

1. G2 voltage may be increased

2. 3-cathode voltage may be decreased

3. Picture tube may short

4. G1 voltage may not be grounded


168

White Balancing in TV receivers

Aim:

To perform white balancing in TV receivers.

Theory:

White balancing is very much necessary in colour Television receivers to reproduce good quality picture

and sound. It should be carried out when the yoke is to be replaced with another. Also, if the cathodes of

the picture tube becomes weak, the reproduced picture would suffer interferences from other colours. At

this time too, white balancing is essential.

This is a procedure by which we adjust the intensity of (R-Y), (B-Y) and (G-Y) signals so that a pure

monochrome signal is obtained in the receiver.

Procedure:

1. Open the back cover of the receiver

2. Turn colour control to the minimum position and see whether there are any traces of any colour

on screen. If any traces are observed, white balancing is not correct.

3. Now reduce colour, contrast and brightness to zero so that no picture appears on screen.

4. Increase screen voltage sufficiently that the picture appears on the screen.

5. Now adjust the presets ((R-Y) Cut off, (B-Y) cut off and (G-Y) cut off) so as to obtain a proper

monochrome picture on screen.

6. Reduce focusing voltage and increase contrast and brightness to sufficient level. If focusing

voltage not reduced, retrace lines will be observed on screen.

7. Still if pure monochrome picture not obtained, adjust the two drive presets on the neck board of

picture tube to obtain monochrome picture. The presets can be R,G or R,B or G,B.

8. Now increase colour so as to obtain a good clarity picture.

Result:

Carried out white balancing adjustments in Colour Television Receiver.


169

TECHNICIAN CONTROLS IN COLOUR TELEVISION RECEIVER

AIM

To study about the technician controls of a colour television system and to familiarize with the way of adjusting these controls to produce good quality picture.

Theory

Correct adjustments of technician controls are necessary for the proper functioning of the receiver. If proper picture with true colours cannot be obtained with operating controls, adjustment of the relevant service controls should be attempted.

Common servicing controls in a colour television receiver are Horizontal Oscillator control, Vertical Oscillator control, Height control, Focus control, AGC delay control, AFT control, Colour subcarrier frequency control, Colour purity adjustment, White balancing adjustment and Convergence adjustment.

Horizontal Oscillator adjustment: If horizontal frequency drifts away from 15625Hz, horizontal synchronization will be lost resulting in horizontal instability (picture tears apart). If this happens, horizontal frequency should be adjusted with horizontal oscillator control. Procedure

1. Adjust horizontal frequency control till the picture stabilizes. 2. Now rotate this control to one side till the picture just looses horizontal synchronization. Next rotate this

control to the other side till the picture again loses synchronization. 3. Adjust the control to a centre position of the two settings where the picture just lost its synchronization.

Vertical Oscillator Control: This control should normally be adjusted to provide a stable picture (V-Hold) Height Control: The picture height should be slightly more than the height of the screen. Adjust the control so as to obtain this. Focus Control: Correct focusing of the electron beam depends on the focusing voltage given to the focusing anode of the picture tube. If the focusing is not proper, it should be adjusted with the focus control provided on LOT. Automatic Gain Control: In most of the colour TV receivers, adjustment of only the delay of RF AGC is provided. Normally the factory adjustment of this control should be satisfactory. However if any component is replaced in the AGC circuit or if there is overloading on a strong channel, RF AGC control should be adjusted as follows.

a. Tune the strongest station available in the area. b. Turn the AGC delay control for minimum gain (fully counter clock wise). c. Now adjust the control until snow disappears from the screen.

Automatic Fine Tuning: AFT control adjusts the oscillator frequency automatically to maintain correct tuning of the channel.

a. Place the AFT switch to OFF. Tune the receiver to an active channel and adjust the fine tuning control for best picture.

b. Now switch ON AFT and adjust the AFT transformer core till the best picture is obtained.

c. Check the pull in action by tuning the fine tuning control to both sides.

Colour Sub carrier Control: Colour sub carrier control provides adjustment of the free running frequency of the colour subcarrier oscillator. If the frequency of the oscillator drifts beyond pull – in range, it will loose synchronization and the colours would not be stable.

a. Tune in colour pattern from Pattern Generator and let the receiver warm up for 5 or 10 minutes. b. Earth the subcarrier bursts given to sub carrier oscillator. c. Earthing will bring colour killer into operation thus blocking the chroma amplifier. Turn off the colour killer

by using suitable means. d. Adjust the colour subcarrier control till the colour bar pattern stands still or drifts slowly across the picture

tube screen. Result: Studied the adjustments of technician controls of CTV receiver


170

PURITY AND CONVERGENCE ADJUSTMENTS


171

PURITY AND CONVERGENCE ADJUSTMENTS

Aim:

To carry out purity and convergence adjustments in a colour television receiver

Procedure

Colour Purity Adjustments: Colour purity adjustments are carried out to ensure that the electron beams from each gun should strike the phosphor dots of respective colour only. If the colour reproduction is not pure, this can be due to either magnetization of the picture tube or due to wrong adjustment of the colour purity magnets.

a. Switch ON the receiver and let it warm up for at least 15 minutes

b. Turn the contrast and brightness control to maximum.

c. Adjust the red and blue cut off controls to provide only a green raster. Advance the green cut off control if necessary.

d. Loosen the clamp screw holding the yoke and slide the yoke backward or forward to provide vertical green belt on the screen of the picture tube.

e. Centre the raster vertically by adjusting the colour purity magnets.

f. Move the yoke slowly forward and backward until a uniform green light is obtained on the screen. Tighten the clamp screw.

g. Check the purity of the red and blue rasters by adjusting the cut off controls.

h. Tighten the screw of the yoke temporarily.

i. Proceed the grey scale adjustment.

Convergence Adjustments

The convergence adjustments are done to achieve the convergence of all three electron beams in correct planes. These adjustments are in two parts – centre convergence adjustment (static convergence) and circumference convergence adjustment (dynamic convergence).

Static Convergence

i) Feed cross hatch pattern from the pattern generator and adjust the brightness and contrast controls for a well defined pattern. If the centre convergence is correct, a cross hatch pattern with pure white lines should be visible. If different colour lines appear, the convergence is not correct.

ii) Adjust the two tabs of the four pole magnets to change the angle between them till the red and blue vertical lines are superimposed in the central area of the picture tube screen. Now turn both the tabs at the same time keeping the constant angle to superimpose red and blue horizontal lines at the centre of the screen.

iii) Adjust two tabs of six pole magnets to superimpose red/blue line and green line. Just as in the case of four pole magnets, change of angle between the two magnets affects the horizontal lines.

iv) Repeat the adjustments ii and iii till pure white cross hatch pattern is obtained.

Demagnetising the picture tube

An automatic degaussing coil mounted across the colour picture tube demagnetizes the picture tube every time the receiver is switched ON. If the set is moved or faced in a different direction, the power


172


173

must be switched off for at least 10 minutes (this is the time required for PTC thermistor, connected in series with the degaussing coil to cool down and allow normal current flow through the degaussing coil).

If the chassis or parts of the cabinet become magnetized resulting in poor colour purity, the picture tube should be demagnetized using external degaussing coil.

For this, connect the degaussing coil to the mains and slowly move it around the face plate of the picture tube, the sides and front of the receiver (but keep it away from the loud speaker) and slowly withdraw the coil to a distance of about 2 metres before disconnecting it from the mains. If the colours are still impure, perform the colour purity and convergence adjustments.

Result

Studied about the technician controls of Colour Television receiver and familiarized with the methodology of adjusting these.


174

Series Voltage feedback Regulator

Tabulation Column

Load Current Constant Input Voltage Constant

Input Voltage Output Voltage Output Current Output Voltage

6V 7mA

7V 8mA

8V 9mA

9V 10mA

10V 11mA

11V 12mA


175

Series Voltage feedback Regulator

Aim

To construct a Series feedback Voltage regulator as used in Monochrome and Colour Television

Receivers.

Materials Required Transistor – BC148 (2 Nos), Resistors – 4.7K (2 Nos), Potentiometer Zener diode Principle The series feedback voltage regulator is one of the most efficient voltage regulators. The circuit contains 3 elements. They are Reference Element, Sensing Element and Control Element. Q2 and R1 acts as sensing element, Zener diode and R2 acts as reference element, Q1 acts as sensing element. Sensing element compares the output voltage with reference voltage. Any variation in the output voltage produces difference voltage which is applied to the control element by the sensing element. As a result, the resistance of the control element varies in a manner so as to oppose the original change in the output voltage and the output voltage remains constant always. Procedure

1. Rig up the circuit 2. Apply a dc voltage from a variable power supply. 3. Make the load current constant and vary the input voltage. Measure the output voltage in each

case. 4. Make the input voltage constant and vary the load current. Measure the output voltage in each

case. 5. Tabulate the readings

Result

Constructed the series feed back voltage regulator.

Studied its working when both the input voltage and load currents are varied


176

Understanding VCRs

Video Cassette Helical Scan recording

http://science.howstuffworks.com/enlarge-image.htm?terms=vcr&page=0


177

Understanding VCRs Aim: To study the working of a VCR.

The VCR itself has two jobs:

It must deal with the tape -- an extremely thin, fairly fragile and incredibly long piece of plastic. It must read the signals off of the tape and convert them to signals that a TV can understand.

In sound recording, the sound information is stored linearly on the tape. That is, the tape moves past the recording head and the sound information is laid down as a long line following the length of the tape. The tape might move past the head at a speed of 2 or 3 inches (5 - 8 cm) per second. A video signal contains perhaps 500 times more information than a sound signal, so the same approach cannot work. The tape would have to be moving past the head at a rate of many feet per second.

To solve this problem, two recording heads are mounted on a rotating drum that is tilted with respect to the tape. The data recorded on the tape looks as shown.

Since the drum contains two heads on opposite sides of the drum (180 degrees apart), the two heads alternate, each one reading or writing every other band. The top linear tracks represent the audio and control tracks. The control track is especially important:

It tells the VCR whether the tape was recorded in SP, LP or EP mode. It tells the VCR how quickly to pull the tape past the drum It gets the heads lined up with the bands during playback.

When you play with the "tracking" control on your VCR, what you are doing is adjusting the skew between the control track and the actual head position on the tape. Usually, this is not necessary, but if a tape is badly worn or stretched you may have to adjust the tracking.

The head is rotating at 1,500 revolutions per minute (rpm), or 25 revolutions per second. Obviously, the rotating head approach, also known as helical scanning, saves a lot of tape.

The only problem this creates is that a VCR designer has to get the video tape to wrap around the rotating head in order to record or play back the tape. In addition, the device has to read the audio and control tracks from the tape, keep the tape moving at exactly the right speed and detect the end of the tape. To do all of this, the tape has to follow a tortuous path, as shown

When the tape is first seated in the VCR, these two rollers are actually inside the cassette, behind the tape. The cassette has cutouts to allow these rollers to fit into the cassette.

Once the rollers fully extend on their tracks, the tape fits very nicely around the drum:

The pinch roller and inertia roller engage, and the tape is pressed onto the erase and audio heads. It's like watching a ballet when you see all of this take place -- there are some pretty amazing mechanical engineers working on this stuff!

Result: Studied the working of VCR.


178

Cleaning of VCR Heads


179

CLEANING OF VCR HEADS

Aim: To clean VCR Heads

Materials required

VCR head cleaning tapes VCR head cleaning fluid Q tip swabs Assorted screw drivers. Latex gloves if you have them. Isopropyl Alcohol. Procedure

1. First thing to try is putting a tape head cleaning cassette in the VCR. Scotch makes a good one. The one shown requires no solvent. Just put the tape in and when it's done in a few seconds it will let you know. See the next step. If this works, great, if not keep reading.

2. When the Scotch tape head cleaner has done all it can do, you will get this message on your TV screen which tells you to stop the VCR. Try a Video tape now and see if the situation is improved. If not, keep reading.

3. There are several types of these. One type requires the addition of a little solvent to a webbing wound in a cassette. With this one you run the cassette a few seconds then try a Video and see if it's improved. If not, keep reading.

4. If none of the above work, you can get into the VCR and clean the heads by hand. The heads are that round aluminum colored object in the center of the picture. Here is how you do it. Take the cover off the VCR. This should be a very simple task of just removing a few screws and lifting it off. Dip a tip swab in some head cleaner solvent if you have it or some isopropyl alcohol and run it around the head as shown. DO NOT TOUCH THE HEAD WITH YOUR FINGERS!!! If you have latex gloves it's OK to put them on. Then you can turn the head at the very top flange with a finger. You can do this any time you need to. Good viewing.

How to Clean Inside a VCR

As with any appliance in your home, dust and dirt will build-up inside your VCR over time. Don't think that just because the mechanical pieces inside are protected by a case that dust can't work its way inside to coat the components. Especially sensitive are the VCR heads that are responsible for reading the magnetic encoding on the VCR tapes and turning that code into picture and sound. Dust can harm your VCR and with enough build-up, can prevent it from working altogether. At the very least, too much dust can compromise the clarity of special projects, such as copying VCR tapes to DVD. The inside of your VCR and the VCR heads are easier to clean than you might think, and cleaning them is essential to keeping your VCR in top working condition.

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Materials Required

b) Dust cloth c) Can of compressed air d) Head-cleaning cassette or unused cassette tape e) Rubbing alcohol and cotton swabs

Procedure

1. Unplug your VCR.

2. Clean the outside of the VCR so that any dust or dirt coating the outside does not find its way back inside the machine.

3. Push the cover of the cassette bay inward with your fingers as if you were inserting a cassette. Hold the bay open.

4. Insert the nozzle of a can of compressed air into the cassette bay and fire the compressed air into the unit. This will loosen and blast away the dust and dirt that is coating the general interior of the VCR.

5. Clean the VCR heads. There are different ways to clean them, but the easiest and most common is to use a commercial cleaning cassette. This is a cassette that is designed to clean the heads with cleaning fluid. Simply insert the cleaning cassette into the VCR as you would a tape cassette and press "Play." The cleaning cassette will do the rest.

6. An alternative to the commercial cleaner is to use a new, blank cassette tape. Insert the new, blank cassette into the VCR and press "Play." Allow the tape to play from beginning to end and the heads will be cleansed in the process. It is also possible to clean the heads manually by removing the outer cover of the VCR and gently rubbing the heads with alcohol-soaked cotton swabs.

Result

Cleaned VCR heads


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CD/DVD PARTS

The surface of the compact disc contains billions of microscopic small holes. These holes contain the digital (zeroes and ones) coded information. From this, (a) The sound will be reconstructed, (b) the speed is controlled, (c) the laser beam will be controlled and (d) the errors will be corrected. A laser beam senses the recorded information. There is no contact between the disc and the sensing system. The reflected light, via a prism, hits a photo detector and will be converted into an electrical signal.

The track will read from inside to the outside with a speed decreasing from 500 till 200 rotations per minute. The total track length is about 30 km.

CD and DVD Belts


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Parts of a CD Player

1. Casing

The internal components of a CD player are protected by an outer enclosure made out of steel or plastic, which may include a headphone/stereo jack and/or an AC adapter jack.

2. Drive Motor

The drive motor of a CD player is a small motor that is designed to spin a CD at a rate of 200 to 500 revolutions per minute (RPM).

3. Laser

The laser in a CD player is created by a semiconductor known as a laser diode, which focuses light on the surface of the CD.

4. Lens/Sensor System

CD player focuses its laser through a series of lenses that shine light onto the CD and bounce the light back up to sensors that decode the information.

5. Tracking Mechanism

The tracking mechanism of a CD player moves the laser, sensors and lenses down the tracks of the CD so the player can read each track.


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MOTHERBOARD LAYOUT OF A CD PLAYER


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MOTHERBOARD LAYOUT OF A CD PLAYER

Aim: To get familiarized with the layout of a CD Player and understand about the ICs used in the system.

Theory

1 is the main programme IC (Eg. SST27SF020). This IC handles DISPLAY and COMMANDS. This IC is

an EEROM (Electrically Erasable Read Only Memory) and can be programmed subsequently after

detaching it from the Mother Board using an external programmer with 12V power supply. These devices

can retain data for more than 100 years. Read operation requires 4.5 – 5.5V. So base pin is provided for

this IC, where as all other ICs are soldered directly to the board.

Faults: a) All functions of VCD may stop b) No Play c) No MP3 reading d) Tray may get

in/out but optical unit may not read the disc e) No forward/reverse f) Disc may stop often g) Player

may not turn on h) Player manufacturer logo may not display i) all functions may not work

2 is the Visba 3 (128 pin) VIDEO PROCESSOR IC. Its features include Dual CPUPMP core, integrated

TV encoder, VCD 1.1 and 2.0 compatible, Composite/S video output, NTSC/PAL formats, audio and video

error concealment, smart bright feature for adjusting brightness of movies during play back, zoom in/out

4x magnification, video CD 2.0 play back control, dual microphones output, 7 band graphic equalizer,

karaoke voice recording, programmable master clock for external audio DAC, digital echo up to 168ms

delay, MP3 audio playback, direct servo control, 4 bit OSD controller etc.

Faults: NTSC/PAL system fault, No CVS/S-video out, No sound/faulty sound/surround sound/3D

sound, Microphone input not working, Remote power on/off standby not working

The IC, GM71V18163CT6 marked (3) makes and gives commands to other ICs for their working. If

something happens to this IC, system will be dead. (If ICs marked 1 and 2 goes defective, system will not

be dead)

(6) is the 9290x02 IC is used for signal processing. Its features are EMF data demodulation, Frame

sync detection, error correction, interpolation, digital audio interface, CLV servo control (x1, x2), digital

filter etc.

(4) is the 9226x01 IC which is a low voltage, low current consumption one that can read CD-RW

and CD-R discs and can be applied to various products such as VCD, disc man etc. main features are RF

amp, gain setting for CD-R, CD-RW, RF offset adjustment, focus error amp, tracking error amp, center Y

amp, Automatic Power control, RF AGC and EQ control, Loop for spindle, focus, tracking servos, fast

search mode etc.

Note: If Visba3 IC goes defective, there won’t be colour, only black and white.

5 is the IC which loads all commands and is known as loader IC. So it is provided with heat sink.

Supply to all motors is from this IC.

Result:

Studied about the layout of the motherboard and the functions of different ICs used.


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Fix a Skipping CD Player Aim To fix a skipping CD Player Procedure

1. Because skipping can be caused by vibration, ensure the CD player is stable.

2. If stability is not the problem, use a cleaning disk to clean build-up on the laser lens. You may also clean the lens with a cotton swab dipped in rubbing alcohol.

3. If the CD player continues to skip, the tracking mechanism inside the player may be dirty, causing the laser arm to catch while it is gliding back and forth. Clean the tracking mechanism by carefully spraying compressed air into it.

4. If the player still skips, your CD read head may be misaligned. Before opening the case to attempt realignment, consider the fact that taking apart your player means your warranty is no longer valid.

5. Disconnect the CD player from its power source and/or remove batteries at least 30 minutes before taking the player apart.

6. Open the case of the player by removing all screws. Use as little force as possible.

7. Locate the CD tray and the arm that hovers over the closed tray. This arm holds the lens.

8. Now locate the small motor that moves the arm.

9. Look for a small square component on the circuit board attached to this motor. There should be a plastic disk on top with a slot for a flat head screwdriver.

10. With a marker, mark the current position of this component, called a potentiometer. This way you'll know where it was originally positioned and how far you will have adjusted it.

11. Adjust the potentiometer using a flat head screwdriver in small increments, testing the results of each adjustment. Carefully plug in the device. Touch only the "Play" and "Stop" buttons. Unplug the device for 30 minutes before making additional adjustments and retesting.

12. Reassemble the player.

Result

Corrected the CD Player which was skipping


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REPAIRING A SCRATCHED CD/ DVD

Aim

To repair a scratched CD/DVD

Procedure:

1. Examine the surface of the CD/DVD. Try to find the location of the scratch or skip.

2. The skip could be caused by grease or dirt, so the first step is to clean the entire

CD/DVD with a damp, soft cotton cloth .

3. Rinse your disk in tap water and dry with a lint-free cloth.

4. Rub a small amount of toothpaste on the scratches of the CD with a cotton swab

until the scratches have disappeared. Use small circular motions around the scratch

to fill with toothpaste. Circle the cotton swab from the centre to the outside edge.

5. Let the toothpaste sit for a few minutes. Use a lint-free cloth and wipe in a straight

line from the center of the disc to the outer edge

6. Rinse under cool/warm water and remove all toothpaste. Dry with a soft cloth.

7. If this doesn't work, buy a DVD refinisher. This is a little device that spins and

polishes DVD's, taking out the scratches in the bottom layer of plastic.

Result

Repaired a scratched VCD/DVD.

It works well when inserted in a CD/DVD Player


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FIXING AND MAKING CDS/DVDS PLAYABLE AGAIN

Aim:

To make faulty CDs/DVDs playable again by applying wax

Procedure

1. Turn CD on side that is where laser reads it. Do not repair side with writing or

logs on it. Get the wax and rag ready. You can use any kind of car wax, such as

Turtle wax. Polishes do not work as well.

2. Rub small amount of wax on cd in up and down motion. Do not rub it in

circular motion. This works with even new discs to protect them. Let sit for a

minute.

3. Let it haze up and wipe the same way as you did to polish the disc. You may

have to do it twice. You may still see some scuffs and scratches on the disc,

but what you will be doing is fill them in with the rubbed in wax. The disc

should now be playable and should last, if handled with care for a long time.

Result

Made the faulty CDs/DVDs playable again by applying wax on them


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HOW TO BUY A CD/DVD PLAYER

Aim

To understand the basic facts before buying a new CD/DVD player

Procedure:

1. When looking for a DVD player for your television, remember it can also be wired to your stereo,

for a full and rich audio track, as well as that widescreen HD picture

2. Decide on what kind of DVD player you’re going to purchase. DVD players have many features

these days, including parental locks, digital video output, playback of not only regular CDs but

MP3 audio and picture CDs, and progressive-scan capabilities.

3. When buying a DVD player, be sure to choose whether you want the unit to run more types of

disks, such as CD ROM's, and Audio CD's. Will one of the thin, streamlined models fit best in

your current entertainment center, or can you pick something a little more bulky, with a few

more features?

4. Consider your budget. DVD players are fairly inexpensive these days, but that is just your basic

model. If you are looking for something a little more advanced, you should pay fairly high.

5. Keep in mind that all DVD players come equipped to play video CDs, but only video CDs that are

mass market produced. Any CDs burned on your home computer will not play unless that is a

special feature of the DVD player, which will probably cost more money.

6. Make sure the DVD comes with a full remote control.

7. Make sure the DVD can handle higher resolutions, as televisions change over to higher

resolutions and HDTV signals.

Result

Understood the facts before preferring to buy a new CD/DVD Player

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HOW TO PROLONG THE LIFE OF A CD/DVD PLAYER Aim To understand the procedures about how to prolong the life of a CD/DVD Player Procedure:

1. If possible, keep your player/recorder in a cabinet. This really reduces the amount of foreign particles entering your system.

2. If you have bought a DVD player lately, you may receive a micro fiber cloth with the packaging. This is really great for the outside of the system. You can get electrostatic cleaner just about anywhere.

3. Ok, now for the inside. The Lens is one of the most important part of your player/recorder. This is what reads all the vision, and audio information. You can get a wet/ Dry cleaning system by paying little, and it is well worth it. Especially if you rent DVD's.

4. Read the directions on your Lens Cleaner. There are two little fine brushes attached to the cleaning disk (usually Black and white). You only put ONE drop of the cleaning solution on one of the brushes. When you insert the disk, the instructions will be played. It usually says to clean every ten hours of play.

5. If your player has openings for connecting portable flash memory devices or a slot for a memory card. SD disks, micro, or any other openings; flatten your micro cloth and swipe the dust out, Do not use anything wet.

Battery Life 1. Allow a new battery on a portable DVD player to completely charge before using it. A portable DVD

player's battery is usually a rechargeable lithium model, and as such it will develop a memory that greatly depends on how much it is filled to capacity the first time it is charged. Filling the battery to full capacity before using the portable DVD player will significantly prolong its life, while the battery will only last half as long as it would otherwise if you were to charge it to 50 percent of its full capacity.

2. Drain the portable DVD player's battery completely before charging it up again. This also relates to the idea of a battery's memory, because if a battery is charged before it has been completely drained of power, it will have a slightly shorter life than it did when you first charged it. Subsequent charges and not allowing the battery to drain will further shorten its life, until the battery cannot hold a charge that is useful to the portable DVD player.

3. Avoid charging the portable DVD player's battery to any point less than full power. This is also related to a rechargeable battery's memory, as charging a battery to less than its full power will cause the battery to develop a shorter charge. Recharging the battery fully allows it to keep its original memory of how much of a charge to hold, and it prolongs the battery's life.

4. Keep the battery safe from power surges. A power surge can overload a portable DVD player's battery or severely reduce its memory capacity, among other harmful results. Invest in a surge protector for your portable DVD player, preferably one that lets you plug in other devices while charging it, and use it for other electronic items you want to protect from a power surge.

Result

Understood the procedures to prolong the life of CD/DVD Player

http://www.ehow.com/how_2214500_prolong-battery-life-portable-dvd.html


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CLEANING DIGITAL CAMERAS Aim

To know how to clean Digital Cameras

Theory

Cleaning digital cameras will help them to last longer and take better pictures. If you think your

camera is not working well a good cleaning can save you the time and expense of a repair. Cleaning a

camera lens will help you are take sharp photographs. Cleaning the LCD will allow you to view each

photo clearly before having them printed. Camera Maintenance is an important part of keeping your

digital camera working properly. However, it is a delicate piece of electronics. Make sure you have the

correct supplies and take your time. This process is best used for point and shoots digital cameras. If

you own a more complicated camera, please refer to your owner’s manual.

Procedure:

ii. Carefully clean the digital camera lens. Never touch the lens with your fingertips and only clean

when absolutely necessary. Turn on the camera and gently blow on the lens. If particles still remain

use your soft lens brush to gently brush away dust If you have stubborn dirt or smudges use a micro

fiber cleaning cloth and gently wipe off the camera lens. If your lens is still smudged, put a few

drops of lens cleaner or water on the microfiber cloth and wipe again. Never put water or cleaner

directly on the lens. Use your lens caps to keep the lens clean longer.

iii. Clean the cameras LCD screen next. Turn off the camera to be able to see the dust and smudges on

the screen. Use the soft brush or micro fiber cloth to remove dust. If you have smudges, add a few

drops of water to the cloth and wipe gently. Never put water or cleaner directly on the LCD screen.

iv. Clean the viewfinder and the front of the built-in flash. Use the same method as described above.

v. Clean the body of the digital camera by wiping it with a lint-free or micro fiber cloth. Use the soft

brush to clean around the battery, memory card, power adapter and USB slots.

Result

Understood how to clean Digital Cameras

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VIDEO COMPACT DISC, VCD


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VIDEO COMPACT DISC, VCD

Aim: To Study about CD Player

VCD or Video CD is a new video format that offers exceptional high – end digital picture quality and smoothness, over an hour of playing time with full CD-quality stereo sound. The signal on the disc is stored as digital data in the form of 1s and 0s (pits and flats)

Optical pick up assembly

The pick up assembly basically consists of

1. A low power LASER diode to illuminate the VCD tracks. 2. Lens and prism adjustment to direct the laser beam to the VCD surface and to direct the reflected

laser beam towards photo-diode array. 3. A photo diode array to obtain data, focus and tracking signal from the reflected laser beam. 4. Focus and tracking coils to focus the laser beam to the VCD surface and to move the assembly to

proper track across the disc surface In the optical pick up unit, the laser diode emits laser beam from a small point into an

elliptical or conical distribution. The beam is passed through various prism and lens to form a very small diameter light beam on the disc surface at the centre of the track.

The objective lens is controlled by the tracking and focusing coil to keep the beam focused on the VCD and to keep the condensed beam at the centre of the track.

The laser beam is reflected back by the pits and flat areas on the disc surface. This reflected beam is applied to a group of photo diodes through objective lens, collimator lens and some prism arrangements.

The photo diodes induce voltage according to the reflected beam falling on it. Focus error and tracking error voltage generated by this photodiode array is applied to the tracking and focusing coil to control the objective lens.

Data signal generated by this photo diode array is sent to an amplifier to ampify the data signals picked up from the disc. The output from the amplifier is processed to produce the audio/video signal stored on the disc surface.

3 types of optical assemblies which are commonly used are, 1. Single – beam radial tracking 2. Single – beam linear/straight line tracking 3. Three beam linear/straight line tracking.

Single – beam radial tracking

In single – beam radial tracing method, the objective lens can only move vertically for focusing, but has no horizontal movement for tracking. The beam splitting prism is used to produce two beams from the single laser beam. The photo – diode array comprises of four photo diodes from which the data, focus error and tracking error signals are obtained.

Single – beam linear/straight line tracking

This type of objective lens has the capability of moving vertically to achieve focus, and also it has limited horizontal movement of about 2 mm for tracking.


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http://www.alibaba.com/product-gs/240921793/CD_VCD_Optical_Pick_up_Laser.html


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The reflected beam from the disc surface is directed through a semi transparent mirror towards the photo – diode array comprising of four photo diodes. Output from these photodiodes are used to develop the data, focus error and tracking error signals

Three beam linear/straight line tracking.

This is the most commonly used optical assembly. In this type, three laser beams are generated from a main laser beam, the main or center laser beam provides data retrieval as well as focus error information and two side beams provide tracking error signal.

In this assembly, the objective lens can move vertically to achieve focus, and laterally (horizontally) for tracking, i.e to move to the center of track.

In this assembly, the laser diode produces only one laser beam, other two beams are obtained from this single beam by using a diffraction grating.

As the lens has limited amount of lateral movement, the complete assembly is moved gradually across the surface of the disc to read the signal on the VCD surface.

Objective lens: Objective lens is controlled inside to optical unit using the procedure used to move the voice coil inside a speaker. The lens is mounted on a ring of magnetic material and is connected to the main housing using two leaf springs.

The housing contains a focus coil which produces magnetic fields based on the focus error signal received from the photo detector diodes.

The magnetic field moves the objective lens up or down based on the polarity and strength of the focus error current in the coil.

Laser diode: Laser diode produces laser beam of 780 nm wavelength. Power of the laser is in the range 0.2mW to 0.12mW.

To maintain the constant output level of the laser diode, a portion of laser output through a photo or monitor diode is fed back to an Automatic Power Control (APC) circuit where it is compared to a predetermined level and adjusted by the laser power control. When the intensity of the main laser beam increases, the APC circuit will reduce the beam intensity by reducing the laser diode current.

Diffraction Grating: Diffraction grating is an extremely small special lens that produces three beams from the single beam of the laser diode. This is used only in the three beam optical pick up devices. Two side beams generated by the diffraction grating is used to maintain proper tracking by the three beam tracking servo.

Prism: This prism is used to separate the direct laser beam going towards the disc and the laser beam which is reflected from the disc surface. The prism will direct the reflected laser beam towards the photo diode array for processing.

Semitransparent Mirror

This allows the direct laser beam from the laser diode towards the collimation and objective lenses and onto the disc surface

Collimation lens: The collimation lens is used to produce completely parallel beams of laser.


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This lens together with the objective lens is used to focus the laser beam to the disc surface.

Quarter Wave Plate: The direct laser beam going towards the disc surface when passed through this plate gets optically rotated by 45 degree. The reflected laser beam is further rotated by 45 degree when the beam passes through this for the second time.

Cylindrical lens: The main function of this lens is to make sure that focus of the laser beam on the playing surface of the disc is maintained.

Photo diode array: Inside the optical assembly. Laser beam reflected from the disc surface strikes photo diode array to produce the three main information required by the VCD player. These information are

1. Data information, which is used to enable the audio or other information stored on the VCD to be produced.

2. Focus error signal, to make sure that the laser beam remains in focus on the disc while it is being played.

3. Tracking error signal, to enable the laser beam to move from track to track gradually across the playing surface of the disc.

Result

Studied about CD Player and its working.


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Connecting VCD Player and TV receiver using A/V connection

Aim

To connect VCD Player and TV receiver using A/V connection

Procedure

1. Plug male pin at one end of the A/V cable (generally connected to yellow colour cable) into the

video output provided at the back of the VCD player.

2. The female pin at the other end of the same cable should be connected to the video input

provided at the front or back of the TV receiver.

3. Plug next male pin of the A/V cable (generally connected to white colour cable) into the audio

output provided at the back of the VCD player.

4. The female pin at the other end of the same cable should be connected to the audio input (left)


5. Plug the next male pin of the A/V cable (generally connected t Red colour cable) into the audio

output provided at the back of the VCD player (R1 or R2).

6. The female pin at the other end of the same cable should be connected to the audio input (right)


Connecting VCD Player and TV receiver using RF connection Procedure

1. Male pin at one end of the RF cable wire should be connected to the RF output provided at the

back of the VCD player.

2. The female pin at the other end of the RF cable should be connected to the antenna input/

aerial input/ RF input provided at the front or back of the TV receiver

Note

RF connection provide poor result compared to A/V connection, so the RF connection should be used

only when A/V connection facility is not available on TV receiver.

Result

Connected VCD Player and TV receiver using both RF and A/V connections and observed programmes.


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201

Controls of a CD player (Front load type)

Aim

To study about the front panel controls of a CD Player and to adjust them to get a good quality picture and sound.

1. Open/close switch: To open or close the VCD tray. Once the VCD is placed in the tray, the open/close switch can be pressed once again to close the tray. Without the power on, we cannot open/ close carriage assembly. Most of the disc holder can be closed by slightly pushing the carriage, but, never do this.

2. Power: When this button is pressed, power is supplied to the VCD player. 3. Play: Play button can be pressed to play all the tracks on the VCD placed inside the player. 4. Pause: Pressing the pause button can be used to suspend the playing operation temporarily.

During the pause, the motor keeps on rotating the disc but reading mechanisms stays at the same place and the output is turned off. Press this button once again or press the play button to resume the play.

5. Stop/Clear: When the stop/clear button is pressed the play stops, the disc stops spinning and the pickup will return to the starting of the disc. This will also clear any program in the memory of the VCD Player.

6. Program: The player can be programmed to play the tracks on the disc at a different order than the normal serial order, by selecting the required track and pressing the program button.

7. FF/FB or FF/FR: The Fast Forward and Fast Reverse or Fast Back key can be used to quickly forward or reverse the playing of the current track.

8. Call: This button when pressed will indicate the programmed numbers that are to be played next. 9. Repeat: This button can be processed to repeat the play of the VCD being currently played.

Pressing this key will also turn the repeat LED on. 10. Track number indicator: When a new VCD is loaded in the player, this track number indicator

shows the total number of tracks in the VCD. During normal play operation, it shows the track number currently being played by the VCD player. During the programming, it shows the track number selected for programming.

11. Time counter: The time counter shows the total playing time of the disc, when a disc is loaded into the player. During the normal play, it shows the time elapsed in minutes and seconds from the start of the current track.

12. Anti – shock switch: Many VCD players contain an anti – shock switch to allow the VCD to function properly when the VCD is used in some place with large amount of vibration, or when the disc used in the player has many irregularities, ups and downs. In these conditions, the anti – shock switch should be turned on to get proper output from the VCD player. A negative side of this facility is, if a disc is badly scratched, then turning on the anti-shock circuit will increase the sound skipping on the disc. Result Studied about different controls of a CD player and operated its controls


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203

Remote Control operation

Aim: To study about remote control operation of a CD Player

Before using the remote control, make sure that the power supply to the VCD player is ON and the VCD player contains a known good VCD.

When using a remote control, the remote must be in line – of – sight with the remote sensor on the VCD player. Normally a sensor allows the remote to be used within 60 degree in front of the player.

Remote control should be kept within 7 meter from the VCD player.

Never allow high intensity of light to fall directly on remote sensor

When using remote control, there should not be any object between the remote hand set and VCD player front panel.

1. Power: Turn on the power supply of the VCD player. When the player is off, pressing this button will turn on the player and when the player is on, pressing this button will turn off the player.

2. Open/ Close: This button is used to load/unload or open/close disc tray. 3. Volume + button: Pressing this button will increase the volume level, step by step 4. Volume – button: Pressing this button will decrease the volume level, step by step 5. Play: Starts play operation. 6. Pause: Pressing this button stops the play temporarily. 7. Stop: Pressing this key will stop the play operation and take the player into power on position. 8. Next: Pressing this button will show next track from the VCD. 9. Previous: Pressing this button will show previous track from the VCD. 10. Forward: This button can be pressed to move forward on the same track. The VCD player has four

fast forward facility. Pressing the Forward button once will show FF x1 on the screen and the image start to move at a faster rate than normal speed. Pressing the forward button twice will display FF x 2 on the screen and image will move faster than FF x 1 Pressing the forward button thrice will display FF x 3 on the screen and image will move faster than FF x 2 Pressing the forward button four times will display FF x 4 on the screen and the fast forward operation will take place in the fastest speed. During the fast forward operation, when the end of the track is reached and a new track starts, the plays returns to normal speed playback. To start normal speed play during fast forward, press the play button. This will stop the FF operation and normal play resumes. During the fast forward operation, one can see the movie playing at a faster speed, but the sound is muted during the forward operation, so one will not hear any sound.

11. Reverse: This button can be pressed to move backward on the same track. The VCD player has four speed reverse facility. Pressing the Reverse button once will show FR x1 on the screen and the image start to move back at a faster rate than normal speed. Pressing the Reverse button twice will display FR x 2 on the screen and image will move back faster than FR x 1


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Pressing the Reverse button thrice will display FR x 3 on the screen and image will move backwards faster than FR x 2 Pressing the forward button four times will display FR x 4 on the screen and the fast reverse operation will take place in the fastest speed. During the fast reverse operation, when the end of the track is reached and a new track starts, the plays returns to normal speed operation. To start normal speed play from a particular position, press the play button. This will stop the FR operation and normal play resumes. During the fast reverse operation, one can see the movie running backwards at a faster speed, but the sound is muted during the FR operation, so one will not hear any sound.

12. Surround sound Button: When one is watching a video CD film, one can produce surround sound effect by pressing this button. Pressing this key repeatedly will generate one after the other five different effects.

13. Random: When this key is pressed, the VCD player starts playing the tracks on the VCD in random order.

14. OSD button: This button can be pressed to get information about the play and other operations. When this button is pressed, information obout the track being played, total number of tracks on the VCD, remaining time from currently played track, position of repeat function, system information etc. appear on the television screen as On Screen Display. Pressing this key once again will remove OSD from screen.

15. R/L button: This button is used to select Vocal/ Mono/ Stereo during the Karaoke operation of the VCD player.

16. N/P button: This button is used to sect NTSC or PAL system play back. 17. Zoom button: When the player is in pause mode, pressing this button will enlarge the screen

image. 18. Echo + button: During Karaoke play, this button can be pressed to increase the echo level of

sound output. 19. Echo – button: During Karaoke play, this button can be pressed to decrease the echo level of

sound output. 20. C/E button: This button is used to change the OSD language during the VCD play operation. 21. Slow button: This button can be pressed for slow playback of a VCD. During the slow playback, the

image on the screen will play in slow motion but the sound will be muted. By continuously pressing this button, one can get three different slow motion setting. First time when this button is pressed, SLOW 1 will appear on screen and playback speed decreases. Pressing this button for a second time will display SLOW 2 on the screen and playing speed further reduces. Pressing this button once again display SLOW 3 and the play back speed becomes slowest. Pressing this button for the fourth time restores the original playback speed. You can press the PLAY button to restore the normal playback speed during slow 1, slow 2 or slow 3 playback.

22. View Button: The button is used to open a browse or Digest menu for selection of a particular VCD operation. To use this button,


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1. Stop the VCD player operation 2. Press the view button 3. A Digest menu appears on the TV screen 4. From the digest menu, select an option by pressing the option number on

the remote number key. 23. Intro button: This key can be pressed to play all the tracks on the VCD for around 10 seconds

each. This gives an introduction of the VCD placed in the player. 24. Remain Button: This button can be pressed to know the remaining play time of the track being

played. 25. Freeze button: Pressing this button will pause the image being displayed on the screen. The sound

will continue to play. Pressing this key once again will start the normal play operation. 26. Repeat button: This key when pressed make the player repeatedly play a particular track or the

entire disc. Pressing this button once will start REPEAT 1. In this mode, the track being played will be played continuously. Pressing this button once again will select REPEAT ALL, in this mode all the tracks on the disc will be played continuously. Pressing this button once again will select REPEAT OFF and stop the repeat play.

27. Return Button: In Play Back Control (PBC) mode, this button is pressed to go to the main menu. When PBC is off, pressing this button will not have any effect.

28. GOTO Button: When the VCD operation is stopped by pressing STOP button, player remembers the position when the play is stopped. One can resume the play operation from this stopped position by pressing GOTO button.

29. Step Button: Pressing this button will play the VCD step by step. Image will appear e by one on TV screen. Pressing this button once again will cancel this mode and start normal play operation.

30. Mute button: Mute button can be pressed to Stop the audio output during the VCD play. The video output will continue normally.

31. Program Button: This button is used to program the order in which one wants to view the VCD’s content.

32. PBC Button: This button is used to turn on/off PBC mode. 33. Time button: This button is used to start the VCD play from a particular time onwards. If the total

play time of a VCD is 30 minutes, 25 seconds and one want to start the play from 15 minutes 30 seconds, then press the time button. Time ____:____ display will appear on TV screen. Press 1,5,3,0 on the remote handset keypad to start the play operation from the 15 minutes, 30 seconds onwards.

34. Direct access keys: Normally, 0 to 9, total 10 different keys are provided on the remote, one can press a key or a combination of keys to select a track from the VCD.

35. Double digit track access: 10 + button on the remote handset can be used to select a track with two or three digit number values For example, to select track 16, first press the 10 + button. Immediately press 6.

36. Hoist tone button: This button is used to increase the sound tone during the play back. Pressing this key repeatedly will keep on increasing the tone. This key is mainly used during the karaoke play.


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37. Recover tone: Pressing this button will cancel the effect of hoist tone. 38. Reset: Resets the play to the beginning of the first track on the disc. This also puts VCD in standby

mode 39. Manual search keys: Moves forward or backward on the disc to look for a particular track on the

VCD. The forward and backward movement can be done in the play mode. Once the search key is released, the play resumes at the normal speed. If the search key is pressed during the pause mode, then on releasing the key. Player returns to pause mode.

40. Automatic Music Sense keys (AMS) keys: These buttons on the remote control allow disc to be played directly from the beginning or the previous track or from the beginning of the next track. Unlike manual search operation, pressing of these keys will directly take one to the beginning of the previous or the next track on the disc.

41. Clear: This key when pressed clears any program and the repeat instructions given to the VCD player. Result Studied about remote control of a VCD Player and its functions.


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Precautions when using a VCD player Aim: To learn about the precautions while using a CD Player Procedure 1. Player should be used in a clean environment 2. Direct sunlight should not fall on the player 3. Player should not be kept in a place with vibration, dust, extreme heat, cold or humidity. 4. Do not keep player behind TV, this could affect picture and sound quality of the receiver. 5. Keep player away from electric equipments such as room cooler, motor etc. 6. A non – technical user should not open VCD cabinet, it contains high voltage. 7. One should not use excessive force while operating front panel button of the VCD player.

These are soft buttons, which require very light touch for operation. 8. Never use chemical solvents to clean VCD player’s body; this could ruin its finish. Use clean

cloth with some mild soap 9. Before using a VCD player, user should go through the user manual. 10. Mains plug should fit properly into the AC socket, a loose plug could produce noise and other

disturbance during playback. 11. When using the VCD Player, it should be kept in horizontal position, in vertical position the

disc will not rotate properly and the player will not rotate. 12. Before connecting the VCD player to a TV receiver or a music system, mains supply to both the

units should be switched off. 13. Do not use heavy objects such as telephone receiver etc on top of VCD player. 14. Before switching off the player, remove disc from the tray. 15. Sometimes due to moisture n the disc, the player may not work properly. Wipe the moisture

with a clean, dry, soft cloth. Wiping movement should be from centre of the disc towards outer edges, do not use circular motion when wiping/cleaning a VCD.

16. Never use a VCD which is not in good shape, bend broken etc. this will damage the player. 17. After starting the play, if you fine some problem, immediately stop the play by pressing the

STOP button. 18. Other than VCD, do not place any object on the player’s disc tray. This could damage the disc

mechanism. 19. To prevent dust and other pollution from entering the player mechanism, always keep the disc

tray closed. 20. When VCD becomes very dirty, clean it with soft cloth and mild soap water. Dry it completely

before using.

Result

Studied about the precautions while using a CD Player


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TROUBLESHOOTING THE VCD PLAYER

Aim: To understand about the trouble shooting procedure of a VCD Player.

Procedure

Before starting disassembling the player, do the following checks

b. Make sure that the amplifier/stereo to which the VCD is connected is operating properly. c. Make sure that the disc being played in the player is of good quality. d. Check all the external cable and connectors are connected properly and all the proper

switches are on, such as the power on switch etc. e. Check the fuse, if any is all right. f. Check that the plug – in circuit board in the VCD player are inserted properly. Check for

any loose cable, bad solder, broken copper band etc on the circuit board etc. g. Clean the objective lens. This can clear many of the problems of the VCD player such as

intermittent/ poor play, skipping during play, erratic play etc. h. Check that there is no obstruction to the free rotation of the turntable and that the optical

pick up unit can move freely on the rails.

We can categorize the common faults connected with CD Players under the following heads. f) Mechanical - dirt, lubrication, wear, deteriorated rubber parts, dirty/bad limit switches, physical

damage. A dirty lens (coated with dust, tobacco smoke residue, or condensed cooking grease) - easily remedied - is probably the number one cause of many common problems: discs not being recognized, seek failure, audible noise, and erratic tracking, sticking, or skipping.

Cleaning of the lens and any other accessible optical components (usually only the turning mirror,

if that) and a mechanical inspection should be the first things done for any of these problems (and

as periodic preventive maintenance especially if the equipment is used in a less than ideal

environment).

g) Electrical Adjustments - coarse tracking, fine tracking, focus, laser power. However, some CD

players no longer have some of these adjustments. The servo systems are totally digital - they either

work or they don't.

h) Power problems (mostly portables) - weak batteries, inadequate, defective, or improper AC wall adapter.

i) Bad connections - broken solder on the pins of components that are stressed like limit or interlock switches, or audio or power jacks, internal connectors that need to be cleaned and reseated, broken traces on flexible cables, or circuit board damage due to a fall.

j) Electrical Component Failure. These are rare except for power surge (storm and lightning strike) related damage which if you are lucky will only blow out components in the power supply.

Result: Understood about the basic trouble shooting procedure of a CD Player.


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FAULT 1

Symptom: Tray does not open or close properly

A. Tray does not open or close

Procedure:

1. Check the open/close switch (S 318) provided on the front panel is working properly. 2. Check the parts and wiring between the switch and the system microprocessor (IC301) 3. Check whether the loading motor receives a signal from pin12 of IC 102 (servo drive) when

open/close switch is pressed. 4. If signal is coming but the motor is not operating, check motor. 5. If no signal is coming, then the problem could be IC301, IC102 or any other in between parts and

wiring. 6. To find out the trouble giving part, check that there are signals at pins 10 and 11 of IC102 each

time open/close switch (S318) is pressed 7. These signals should invert each time the switch is pressed (pin 10high and 11 low, then vice

versa). 8. Also check for corresponding inverted signals at the pins 33 (open) and 34 (close) of the system

microprocessor (IC 301). If the signals are absent or do not invert when S318 is pressed, then suspect IC 301.

B. Tray opens, but not fully

Procedure 1. In this condition, check that when SW02 is actuated, a a change (low to high) occur in the

signal at pin 48 of system microprocessor IC (IC301) 2. Adjust SW02 (tray open or door open) if required. 3. Also check for any obstruction, binding gears, jammed cross rollers, improperly adjusted guide

rails etc. Any mechanical condition which might prevent the tray from fully opening. C. Tray opens fully, but the loading motor does not stop

Procedure 1. Check for the adjustment of SW02. 2. If after checking, it is found that the switch is operating properly and produce a signal at IC301

– 48, but the motor does not stop, the fault is due to IC-301. D. The tray closes, but not fully and the clamp or chuck does not hold the disc or turntable

1. Check that when CHU switch (SW03) is actuated, a change (high to low) occur in the signal at pin 47 of system microprocessor IC, IC301

2. Adjust SW03 if required. 3. Check for any obstruction, foreign objects in the clamp or chuck hinges and tray and for

wiring that has worked its way out of place. E. The tray closes and the clamp or chuck goes fully down but the loading motor does not stop

Procedure: 1. Check for the improper adjustment of SW03 2. Check for the change from high to low occur at the IC301-47, when the tray is fully in and the

clamp or chuck is fully down the disc.


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REPLACING THE DEFECTIVE TRAY OR LOADING MOTOR

Aim

To replace the defective tray or loading motor

Procedure

Before replacing the motor, first make sure that the motor is defective.

Procedure

1. Check the motor continuity, test the voltage across the motor in operation. Check all possible mechanical problems first.

2. Visually inspect the drawer gear assembly for foreign objects. A dirty open/close switch can cause erratic tray operation.

3. Inspect the button terminals for poor contact. Check the tray switch by shorting a test clip across the switch terminals. Check interlock switches in the same manner.

4. Stripped gears on the loading pulley or alongside the tray carriage can jam or prevent the tray from opening and closing. Carefully inspect both gear assemblies. Check for poor motor terminals and connections.

5. Check the controller signal. Before replacing the new motor, measure the gear and motor pulley settings from pulley to motor assembly.

6. The motor is easy to get replaced. The motor is usually bolted to main chassis. In some units, there may be a separate loading assembly. Locate the loading or carriage motor near the tray and clamper assembly. The bottom cover of the VCD player must be removed or the main chassis pulled up if there is no removable cover. Remove the small motor pulley belt. Remove the pulley if motor wont fit through the chassis hole. Now remove the mounting screws that hold the motor to the chassis base. Make sure that the motor is installed with correct polarity in the circuit. Result Replaced the defective tray/loading motor of a CD Player


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LASER DIODE PROBLEMS


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LASER DIODE PROBLEMS Aim: To study about different problems connected with LASER diode in a CD Player Procedure: The complete reading process of the VCD player depends on the laser diode producing the laser beam. If the laser beam is absent, then there will not be any EFM signal. If the beam is weak, the EFM signal will also be weak. The monitor diode used to monitor the output of laser diode is also very important. If the monitor diode does not monitor the laser – diode output properly, then the laser beam can change to an incorrect level (high or low). These conditions can produce improper tracking which will produce even weaker EFM signal. The laser diode appears to be inoperative 1. Check the safety lock provided to disable the laser diode is operating properly. Check that the

transistor Q601 is receiving +5V through CHU switch SW03. 2. If there is no +5V, then the fault will be with SW03. When the switch is in the open position,

then +5V is applied to pin 47 of IC301 to indicate that the tray is open or/and the clamp or the chuck is not fully down.

3. This signal disables a number of IC301 system control functions. When the clamp or chuck is fully down, SW03 moves to the close position and the laser diode receives power through Q601.

4. If power is applied to the laser diode and the Q601 through the switch SW03, then look for LASW signal (low) at pin 51 of IC301 and/or TP14 (LASW)

5. If this LASW signal is absent, fault will be with IC 301. If present, check for signal at pin 5 of IC604.

6. If abnormal, suspect D601. Also look for a signal at pin6 of IC 604 from the monitor diode through R629. If abnormal suspect the monitor diode and R629.

7. If signals are present at both pins 5 and 6 of IC 604, then look for the drive signals at pin 7 of IC 604 and the base of Q601.

8. If the signal is absent, then suspect IC604. If the signal is present, then suspect transistor Q601. Pick up does not move to inner limit when power is applied When the VCD is switched on, the optical pick up unit moves to the start of the disc (the innermost part) and the system microprocessor applies a temporary SLR (slide pick up motor reverse) signal to the pick up serv0. This signal is generated by a reset circuit consisting of Q103, Q104 and Q301, which applies a reset signal at pin 24 of IC301. This produces a temporary SLR signal at the IC301 – 60 which is applied to the pick up motor through IC101, IC 604 and IC102. This SLR signal makes the pick up unit to move inward until the inner limit (LMSW) switch SW01 is actuated. The switch and slide (pick up) motor offset adjustment should be set such that the pickup should stop at the point where TOC (table of contents) or the disc directory or the program information on the VCD can be read in full. If the pick up moves to the inner limit when power is applied, but the disc directory is not read properly, try correcting the problem by adjusting the motor offset adjustment.


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Optical pick up assembly inner limit trouble shooting

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If the pick up motor does not operate or operates but does not move far enough in, or continues to run when the inner limit is reached, then proceed check the following The optical pick up unit does not move when power is first applied (if the player is close, you may not be able to see the pick up, but you should be able to hear the movement of the motor) 1. In this condition, check for an SLR signal at IC301 -60 2. If the signal is absent, then suspect IC301 and the associated parts of the reset circuit. 3. If the SLR signal is present but the motor does not run, hhen suspect IC101, IC604, IC102

and the motor itself. 4. Check the motor drive voltage at the output of IC102 and at the motor 5. If the drive voltage to the motor is present, but the motor does not run, then suspect the

motor. 6. If the motor runs but the pick up unit does not move, then this could be due to mechanical

problems such as jammed gears, binding rollers, improperly adjusted rails, etc. The pick up moves, but does not reach the inner limit 1. In this condition, check that the inner limit (LMSW) switch SW01 when actuated,

generates a change (high to low) in the signal at pin 46 of IC301. 2. If necessary, adjust LMSW switch. 3. Check for any mechanical condition that could prevent the pick up from moving to the

inner limits. 4. Before adjusting the LMSW switch, check adjustment of the servo offset. 5. If after adjusting the servo offset the disc can be read properly, then the LMSW does

not require any setting. Note: Generally, the LMSW switch does not go out of adjustment unless someone has tamped with it or some related parts have been replaced, which requires adjustment in the LMSW switch

Result:

Studied about different problems connected with a CD Player.


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Replacing the defective slide motor

Aim

To replace the defective slide motor

Procedure

Before replacing the new motor, measure the motor pulley settings from the pulley to

motor assembly. Locate the slide or feed motor on the main chassis after it is found

defective. Usually, the motor is located close to the bar tracks.

Two small mounting bolts usually hold the slide motor to the bottom chassis. In some

models, the plastic slide motor assembly must be removed before you can get at the

slide motor.

Before placing the new slide motor measure the distance between the outside gear and

the top side of the motor end belt as shown in the figure, so the gear can be correctly

placed on the new slide motor. Make sure that the motor is installed with correct

polarity in the circuit.

Result

Replaced the defective slide motor.

Set working properly


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Replacing the defective spindle motor:

Aim: To replace the defective spindle motor of a CD Player

Procedure:

To replace the new spindle motor, apply uniform force on the unit support plate. Insert the spindle

motor straight while supporting the motor at its lowest section, and ensure accurate alignment to

obtain a height of 12.5mm from the mechanical base top surface.

Make sure that the motor is installed with correct polarity in the circuit.

Clean the lens:

1. To access the lens in a single-play unit, remove the housing and carefully lift up the hold-down clamp to expose the lens. To remove the lens in a carousel player, remove the player housing and unscrew the bracket secured to the top of carousel, then lift off the bracket.

2. Remove dust with canned air or a soft brush. If needed, use a foam swab or camera-lens tissue (not eyeglass tissue) dampened with lens fluid.

Service the disc tray and belt of a single-play unit:

1. Open the housing by removing the screws on the outside of the housing and remove anything

blocking the tray. Press the open-close control to extend tray, and unplug the unit. To remove the

clip-on tray front, brace the tray and slide the panel to one side.

2. Unplug any cables connecting the front panel to the interior. Remove the screws securing the

front panel and gently tilt it off. If the panel won't move, check beneath it for clips or additional

screws.

3. Lift off the hold-down clamp, screw, or spring on top of the disc tray. Gently pull the tray out of

the player. Clean the travel rail and guides with a swab dampened with denatured alcohol.

Lubricate the tray sparingly with white lithium grease.

4. Remove the belt to inspect for dirt, water, or damage. Avoid touching the belt with your fingers. Use tweezers or wear cotton gloves. Clean the belt with a lint-free cloth moistened with denatured alcohol. Replace the belt if it is damaged.

Service the tray motor:

1. Unplug the player and test the motor . 2. A dirty motor plug can make the tray work intermittently. To clean the motor plug, unplug it and

spray it with electrical contact cleaner. Then repeatedly plug and unplug the unit to verify contact.

3. To remove the motor, depress the end of each clip or bale with a finger and lift it up.

4. To replace the motor, carefully remove the drive belt with tweezers or gloved hand, then lift the

motor out of its mount.

Result: Studied about replacing the defective spindle motor.

http://www.fixitclub.com/Parts_Components/Motor.shtml


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DIGITAL VERSATILE DISC, DVD

Aim: To study about DVD Player

A DVD player is very similar to a CD player. It has a laser assembly that shines the laser beam onto the surface of the disc to read the pattern of bumps. The DVD player decodes the MPEG-2 encoded movie, turning it into a standard composite video signal. The player also decodes the audio stream and sends it to a Dolby decoder, where it is amplified and sent to the speakers. A drive motor to spin the disc - The drive motor is precisely controlled to rotate between 200 and 500 rpm, depending on which track is being read. A laser and a lens system to focus in on the bumps and read them - The light from this laser has a smaller wavelength (640 nanometers) than the light from the laser in a CD player (780 nanometers), which allows the DVD laser to focus on the smaller DVD pits. A tracking mechanism that can move the laser assembly so the laser beam can follow the spiral track - The tracking system has to be able to move the laser at micron resolutions. Inside the DVD player, there is a good bit of computer technology involved in forming the data into understandable data blocks, and sending them either to the DAC, in the case of audio or video data, or directly to another component in digital format, in the case of digital video or data.

The fundamental job of the DVD player is to focus the laser on the track of bumps. The laser can focus either on the semi-transparent reflective material behind the closest layer, or, in the case of a double-layer disc, through this layer and onto the reflective material behind the inner layer. The laser beam passes through the polycarbonate layer, bounces off the reflective layer behind it and hits an opto-electronic device, which detects changes in light. The bumps reflect light differently than the "lands," the flat areas of the disc, and the opto-electronic sensor detects that change in reflectivity. The electronics in the drive interpret the changes in reflectivity in order to read the bits that make up the bytes.

DVDs can store more data than CDs because of 1. Higher density data storage 2. Less overhead, more area 3. Multi-layer storage 4. Higher density data storage

Features of DVD Video

1. High quality digital video 2. Support for widescreen movies on standard wide screen TVs (4:3 and 16:9 aspect ratios) 3. Up to 8 tracks of digital audio (for multiple languages), each with as many as 8 channels. 4. Up to 32 subtitle/ karaoke tracks 5. Up to 9 camera angles (different view points can be selected during playback) 6. Menus and simple interactive features (for games, quizzes etc) 7. Multilingual identifying text for title name, album name, song name, cast etc. 8. Instant rewind and fast forward. 9. Instant search to title, chapter, music track and time code

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10. Durable (no wear from playing, only from physical damage)

A comparison of a CD's pit size and track spacing vs. that of a DVD


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11. Not susceptible to magnetic fields. Resistant to heat. 12. Compact size.

Most players support a standard set of features 1. Language choice 2. Special effects play back: freeze, step slow etc. 3. Parental lock. 4. Programmability (playback of selected sections in a desired sequence) 5. Random play and repeat play 6. Digital audio output 7. Compatibility with audio CDs

Supported Formats

DVD movies Just about all players play DVD movies.

Music CDs Most players also play music CDs.

Video CDs Some players can handle this format, which is used mostly for music videos and some movies from foreign countries.

CD-Rs Some players can play content that you create on your own computer.

Audio DVDs A few players can handle this format for high-quality audio. Other Features

Dolby Digital decoder This feature allows the DVD player to decode the Dolby Digital information from a DVD and convert it to six separate analog channels. This feature is not necessary if you have a Dolby Digital receiver, which has a digital input that carries all of the audio information.

DTS decoder This feature allows the DVD player to decode the DTS information from a DVD and convert it to six separate analog channels. Again, this feature is not necessary if you have a receiver with a DTS decoder.

DTS compatible All DVD players are DTS compatible. They pass the digital audio information on to the receiver, which then decodes it.

Simulated surround If you are going to hook the DVD player up to a TV or a stereo system with only two speakers, a DVD player with simulated surround processing will give you some sense of surround sound without the extra speakers.

Disc capacity Some DVD players can hold three, five or even several hundred discs. Since most DVD players can

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Power supply section of a DVD Player


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also play audio CDs, if you buy a player with a high disc capacity you could store your whole CD collection in the machine.

Remote-control type DVD players may come with three types of remotes:

A dedicated remote, which only runs the DVD player A multi brand remote, which can control other components, like VCRs and TVs made by other

manufacturers (Usually, they only support the more common brands.) A learning remote, which can learn the signals from other remotes and assign them to a button (This

feature is useful if you have uncommon brands of components to control.) Connecting the DVD Player

Connecting a DVD player to your stereo receiver (or television, if you don't have a receiver) involves

making two basic connections: audio and video.

Audio The first connection to make is for the audio portion of the signal. There will be several options depending on the receiver you have.

The best choice (if available) is either to use an optical or coaxial) digital connection. These two choices are equal in quality. In order to use either of these, you will need to have both an output on the DVD player, and an input on the receiver. Only receivers with built-in Dolby Digital decoders will have this type of input.

If your receiver does not have a built-in Dolby Digital or DTS decoder, but is "Dolby Digital ready," look for the 5.1-channel Dolby or 5.1-channel DTS. This connection involves six cables, corresponding to different speaker channels: left front, center front, right front, left rear, right rear and subwoofer.

The last option to connect the two components is with analog RCA outputs. This is a two-cable connection, with one cable delivering the left speaker sound, and the other cable delivering the right. This connection will deliver only stereo sound, but it may be your only option if you are hooking up directly to a television, or if you have an old receiver with only two channels. Now let's take a look at the video connection.

The best quality choice is to use component connection. This connection consists of three cables: color-labeled red, blue and green. The quality is superb. However, these connections only exist on extremely high-end receivers and television sets.

The next option is s-video. One cable connects the DVD player to the receiver in this setup.

The last option, similar to the audio setup, is to use the analog RCA video output, usually color-labeled yellow on both ends. This will deliver the lowest quality, but will suffice for most older, analog televisions.

Result: Studied about DVD Player and its functions



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Remote Control


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Remote Control

Aim:

To study about Remote control and its working.

Theory:

A remote control is an electronic device used for the remote operation of a machine. Commonly, remote controls are Consumer IR devices used to issue commands from a distance to televisions or other consumer electronics such as stereo systems DVD players and dimmers. Remote controls for these devices are usually small wireless handheld objects with an array of buttons for adjusting various settings such as television channel, track number, and volume. The remote gave power to viewers. It allowed audiences, for the first time, to interact with their TV. They no longer watched programmes just because they did not want to get up to change the channel.

The invention of the remote control has led to several different changes in television programming. One thing that the remote control led to was the creation of split screen credits.

The basic premise at work in an IR remote control is the use of light to carry signals between a remote

control and the device it's directing. Infrared light is in the invisible portion of the electromagnetic

spectrum.

An IR remote control (the transmitter) sends out pulses of infrared light that represent specific binary codes. These binary codes correspond to commands, such as Power On/Off and Volume Up. The IR receiver in the TV, stereo or other device decodes the pulses of light into the binary data (ones and zeroes) that the device's microprocessor can understand. The microprocessor then carries out the corresponding command.

To get a better idea of how the process works, let's take a look inside a typical remote control -- the universal remote that came with the author's digital cable box. The basic parts involved in sending an IR signal include:

Buttons Integrated circuit Button contacts Light-emitting diode (LED)

To find out more about the parts on a remote-control circuit board, check out Inside a TV Remote Control.

On the component side, the infrared receiver sits on the front of the device where it can easily see the signal coming from the remote control.

You've probably noticed that some remotes only work when you're pointing them directly at the receiver on the controlled device, while others work when you're pointing them in the general vicinity of the receiver. This has to do with the strength of the transmitting LED. A

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http://en.wikipedia.org/wiki/Television

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http://en.wikipedia.org/wiki/Stereophonic_sound

http://en.wikipedia.org/wiki/DVD

http://en.wikipedia.org/wiki/Dimmers

http://en.wikipedia.org/wiki/Television_channel

http://en.wikipedia.org/wiki/Volume

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Sony TV remotes use a space-coding method in which the length of the spaces between pulses of light

represent a one or a zero.


239

remote with more than one LED and/or a particularly powerful LED produces a stronger, broader signal.

Infrared Remote Controls: The Process

Pushing a button on a remote control sets in motion a series of events that causes the controlled device

to carry out a command. The process works something like this:

1. You push the "volume up" button on your remote control, causing it to touch the contact beneath it and complete the "volume up" circuit on the circuit board. The integrated circuit detects this.

2. The integrated circuit sends the binary "volume up" command to the LED at the front of the remote. 3. The LED sends out a series of light pulses that corresponds to the binary "volume up" command.

It carries several chunks of information to the receiving device, including:

a "start" command the command code for "volume up" the device address (so the TV knows the data is intended for it) a "stop" command (triggered when you release the "volume up" button)

When the infrared receiver on the TV picks up the signal from the remote and verifies from the address code that it's supposed to carry out this command, it converts the light pulses back into the electrical signal for 001 0010. It then passes this signal to the microprocessor, which goes about increasing the volume. The "stop" command tells the microprocessor it can stop increasing the volume.

Infrared remotes have a range of only about 30 feet (10 meters), and they require line-of-sight. This means the infrared signal won't transmit through walls or around corners -- you need a straight line to the device you're trying to control. Also, infrared light is so ubiquitous that interference can be a problem with IR remotes. Just a few everyday infrared-light sources include sunlight, fluorescent bulbs and the human body. To avoid interference caused by other sources of infrared light, the infrared receiver on a TV only responds to a particular wavelength of infrared light, usually 980 nanometers. There are filters on the receiver that block out light at other wavelengths. Still, sunlight can confuse the receiver because it contains infrared light at the 980-nm wavelength. To address this issue, the light from an IR remote control is typically modulated to a frequency not present in sunlight, and the receiver only responds to 980-nm light modulated to that frequency. The system doesn't work perfectly, but it does cut down a great deal on interference.

While infrared remotes are the dominant technology in home-theater applications, there are other niche-specific remotes that work on radio waves instead of light waves. If you have a garage-door opener, for instance, you have an RF remote.

Result

Studied about the Remote Control.

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240

TV TUNER CARD FOR COMPUTERS

Observations

Details of Tuner Card used

Internal/ External :

Make :

Specifications :

Details of channels tuned and their frequencies

Channel Tuned :

Picture Frequency :

Sound Frequency :

Other details obtained from the Main Menu


241

TV TUNER CARD FOR COMPUTERS

Aim:

To install the TV Tuner Card so as to view programmes on Computer.

Materials Required: Personal computer, TV tuner card (Internal/External)

Theory

Installation of software for Tuner Card (internal/external) for the operation of any device interfaced

to a computer requires a driving file. Generally in the case of external tuner card installation, driving file

gets automatically installed. But in the case of installing internal tuner card, software should be installed

from the CD provided.

Procedure

1. Connect the tuner card to the computer

2. Install the software if necessary.

3. Connect cable output to the input socket of tuner card.

4. With the help of remote or computer key board, tune the computer to see various

channels.

5. Note down the channel frequencies and other parameters each time the channel is varied.

Result

Installed tuner card successfully in computer and viewed different channels


242

CABLE TELEVISION SYSTEM

Observations


243

CABLE TELEVISION SYSTEM

(Students should conduct this experiment in consultation with a Cable TV Operator)

Aim

1. To identify components/modules used in Cable Television 2. To identify cables/connectors used in CATV] 3. To measure the signals strength by using signal strength meter.

Procedure

a. Identify and record the specifications of CATV equipments/ Modules

(a)Record the name and specifications of the equipments/devices used. (b) Record the input and output connector details of the equipments used.

2. Identify and record the specification of CATV cables and connectors (a) Identify the names of different cables and record them (b) Record specifications of each cable 3. Measure the signal strength and identify the frequency band and channel (a) Familiarize with the signal strength meter and its working. (b) Connect the meter in between the cable and TV receiver. (C)Operate the TV for a particular channel with the help of tuner. Note the channel name and band (d) Record the signal strength as indicated by the meter (e) Repeat the steps for other channels Result Studied how to install Cable TV Network


244

INSTALLATION OF CCTV NETWORK Observation


245

INSTALLATION OF CCTV NETWORK (Experiment should be conducted under the guidance of a CCTV Technician)

Aim: To identify the basic controls and sockets of a TV camera To operate TV Camera To assemble a CCTV Network Procedure

i. Identify the basic parts, controls and input output sockets of a TV Camera a. Identify the parts by referring the manual. b. Record the name and function of each identified part

b. To operate a TV camera (Procedure as directed by technician) A. B. C. D. E. F.

3. To assemble a CCTV Network

(Procedure as directed by the technician)

A.

B.

C.

D.

E.

Result

Studied about the installation of a CCTV network


246

PRACTICAL EVALUATION

Distribution of scores of P.E

Part 1: Identification of the given components and drawing their symbols - 15 score

Part 2: Construction of the given circuit and checking its performance - 50 score

Part 3: Fault analysis of the given faulty equipment and its rectification -40 score

Part 4: Viva Voice - 25 score

Part 5: Observation/Record book - 10 Score

TOTAL - 150 Score

Part 1

Item Evaluation Points Score

Identification of 5 different resistors Type, Colour Coding, Proper identification 5

Identification of 5 different capacitors Type, Colour coding, proper identification 5

Identification of 2 transistors and their leads PNP/NPN, Lead identification, Writing value 5

Identification of miscellaneous components –

Volume Ctrl, LED, Opto coupler etc (4 Nos)

Proper identification of the component and its

leads

6

Drawing the symbols of above components (1/4 x 16)

= 4

Part 2


Circuit Diagram and marking components Correct symbols, Neatness, Component values 15

Setting up the circuit Soldering, Procedure

Output observation

Output measurement

5 + 5

10

5

Recording the voltages, Computation, Graph Plotting Neatness, marking scale on graph sheet, correct

computation

10

Part 3


Analyzing the Given fault Systematic Analysis 10

Procedure for carrying out the rectification Correct Procedure 10

Fault rectification Systematic Working

20

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