Download - Tv Lab Mannual

R.K.D.F INSTITUTE OF SCIENCE & TECHNOLOGY

DEPARTMENT OF ELECTRONICS & COMM. ENGG.

REMOTE CONTROLLED

COLOUR T.V. TRAINER

MODEL CDM101

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PRACTICALS

Specifications of Colour T.V.

Safety precautions

1. To Study the Block Diagram and working principle

2. To Study Electronic tuner section

3. To Study Video I.F. Section with circuit diagram

4. To Study Sound I.F. Section with circuit diagram

5. To Study Horizontal Oscillator section with circuit diagram

6. To Study Vertical Oscillator Section with circuit diagram

7. To Study Colour Picture Tube Section with circuit diagram

8. To carry out V.I.F. alignment with Sweep Generator

9. To carry out S.I.F. alignment with Sweep Generator

10. To measure Video and Audio gain (sensitivity) with Pattern Generator

11. To demonstrate and understand different types of faults

12. To study faults diagnosis method

1

SPECIFICATIONS

1. System : CCIR-B-PAL-G, 625 lines.

2. Power supply : 230V + 10% AC, 50 Hz.

3. Regulation range : 100V AC to 275V AC.

4. Power consumption : 70 watts max.

5. R.F. sensitivity : 50 micro / volt

6. I.F. Frequency Vision : 38.9 Mhz

Audio : 33.4 Mhz

7. Sound output : 5.0 watts minimum.

8. Picture Tube size : 51 cm Diagonal.

9. Tuner Channels : VHFI- 2 to4, VHF III - 5 to 12,

BAND IV & V - up to 100

S-band and Hyper-band.

10. Program Memory : 90 programs.

11. RF input impedance : 75 ohms

12. EHT : 24 KV maximum.

13. On Screen display for setting of all con trols e.g. Volume, Brightness, Contrast, Colour, Channel and band

selection, Tuning.

14. Audio - Video In sockets.

15. Sections : Operating unit and Tuner, Remote Receiver, Video I.F., Sound I.F., Colour

decoder, Video amplifier, Horizontal oscillator, Horizontal driver and output,

S.M.P.S, Vertical , Picture tube, Remote transmitter.

16. Controls : Volume, Brightness, Contrast, Colour, Channel and band selection, Tuning

(Hyper and S-Band tuner).

17. Remote Control functions : Volume, Brightness, Contrast, Colour, Channel selection, Audio mute

18. Standard Accessories : 1. Trainer Unit

2. A operating/Service manuals.

2

SAFETY PRECAUTIONS

1. Do not touch the EHT transformer, EHT Cable, Screen Cable and Picture Tube earthing.

2. Do not bring any metal part near to EHT.

3. Keep alert while measuring Voltages and waveforms of EHT, SMPS transformer and Horizontal deflection

Coil of Yoke.

4. Do not touch the PCB with necked feet.

5. Do not touch 230V AC mains connector and degaussing Coil Connector.

6. Do not touch AC Fuse, DC Fuse and rectifier section in SMPS.

7. Do not touch BU208D and BD508A heat sinks and Collector Body.

8. Do not disturb Yoke convergence assembly.

9. Do not connect SMPS Ground and Chassis ground.

10. Measure all Voltage with reference to Chassis ground only unless specified.

11. Do not alter FOCUS PRESET and SCREEN PRESET o n EHT transformer.

12. Do not very +115V preset towards high voltage end.

13. Do not disturb Video coil and AGC preset in VIF section.

14. Do not very H. Hold preset towards High frequency side.

15. Isolate SMPS section by removing +115V & +20V jumper whil e creating faults in smps section.

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4

PRACTICAL-1

BLOCK DIAGRAM AND WORKING PRINCIPLE

The main functions of a Colour T.V. receiver are as under: -

1. To select the signals of the channel and to amplify these and convert them into IF Signals.

2. To amplify the video and sound IF Signals, to demodulate the video IF Signals to obtain the composite

Video Signal, to mix the two IF signals to obtain the inter - carrier sound IF Signal and to preamplifier

these.

3. To separate the combined luminance (Y) and chroma signals from the video IF Signals and to amplify

these.

4. To separate the luminance (Y) and chroma i.e. U & V (R -Y and B-Y) Signals from the combined video

Signal.

5. To regenerate sub-carrier signal with phase locking with the sub -carrier burst.

6. To decode the chroma signal to obtain the modulated U and V signals and to demodulate them with the

Help of regenerated reference carrier.

7. To combine the Y, U and V signals (Matrixing) to obtain the colour i.e. R, G and B signals.

8. To amplify them and to give them to the respective cathodes of the colour picture which reproduces these

As colour picture with the help of horizontal and vertical swee ps.

9. To produce horizontal and vertical sweeps synchronized with the respective sync signals and to give them

to the respective deflection coil for producing the sweep.

10. To separate the sound IF signal, to amplify, limit and demodulate them, and t o give them to the

Loudspeaker at sufficient amplitude.

11. To provide power at suitable D.C. voltages for operating various stages, providing supply to various

Electrodes of picture tube and for heating its cathode.

12. To provide infrared remote control operations.

These functions are performed by various stages of the T.V. Receiver, which are explained as under.

The Block diagram showing different sections is shown in Fig.1.

5

BLOCK DIAGRAM OF THE COLOUR T.V.

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Figure 1

6

(1) Tuner: -

The signal received at the antenna are given to the tuner through the balun. The Tuner, which consists of

two stages -RF amplifier and converter, partly selects the signal of the desired channel, amplifies it and converts

it in to I.F. signals.

The R.F. Amplifier amplifies the signals with the addition of a little noise as possible and gives the m to

the Mixer. The gain of this stage is controlled by A.G.C.

The Converter consists of two stages:

1. Local Oscillator.

2. Mixer.

The Converter changes the frequency of the incoming signals in to the I.F. The Local Osci llator produces

oscillations at a frequency, which is higher than the picture carrier frequency by 38.9 MHz. (Which is the video

I.F.). The mixer mixes the incoming signals and the oscillations. This results in the production of the video I.F.

(38.9 MHz) and sound I.F. (33.4 MHz). These IF Frequencies are selected and given to the V.I.F section.

The frequency of the local oscillator is controlled by an arrangement known as Automatic Fine Tuning

(A.F.T.). If the frequency of the local oscillator drifts resu lting in shift in the IFs this arrangement automatic corrects the oscillator frequency thus automatically correcting the fine -tuning.

(2) Video I.F. (V.I.F.) Section: -

This section consists of two stages:

(1) Preamplifier and

(2) Main Amplifier.

The preamplifier consists of IC SL 1430.

The main Amplifier is based on IC TDA 3541A.

This Section performs following functions: -

(i) Suppressing the signals of adjacent channels and reducing the level of self -sound signals.

(ii) Amplification of VIF (38.9 MHz) and SIF (33.4MHz) signals.

(iii) Detection of VIF signals to obtain the composite video signal (C.V.D.).

(iv) Mixing of video IF and sound IF Signals to obtain the inter -carrier sound IF signal (5.5MHz)

(v) Producing AGC Voltage and controlling the gain of VIF amplifier.

(vi) Producing delayed AGC Voltage for the tuner.

(vii) Generating AFT Voltage for automatic fine -tuning.

The Saw Filter (BMC389) is used along with tuned circuits to obtain the desired frequency response in

the VIF Section.

The composite video signal (CVD) obtained from this section is given to Chroma section and SIF section.

(3) Sound IF section (S.I.F.): -

The intercarrier SIF (5.5MHz) is given to the sound section based on IC CA1190, which contains two

sub-sections SIF detection and Sound output amplifier.

The SIF signal, which is frequency modulated is amplified, limited and detected. The detected audio

signal is amplified by output amplifier to drive the loudspeaker.

7

(4A) Chroma section/Colour Decoder Section (CD): -

This section consists of two sub -sections: -

(A) Video buffer amplifier

(B) Chroma Section.

(A) Video Buffer Amplifier: -

The CVD signal obtained from VIF section is given to video buffer amplifier which amplifies this signal

which consists of luminance signal -Y, Chroma signals R-Y and B-Y, horizontal sync signal, vertical sync signal

and the colour sub-carrier burst (colour sync) signal. This stage consists of one transistor. The amplified CVD

signal by video buffer section is given to the (i) Chroma section IC TDA 3561A and (ii) Sync Separator in IC

TDA 1940 F (Horizontal section).

(B) Chroma Section: -

Chroma Section is the most important section in a Colour T.V. Receiver. It extracts the colour signals

from the modulated and coded chroma signal and gives them to the R, G, B Video amplifier output stages.

The main functions of the chroma section are -

(1) Amplification of chroma signals (with colour killer)

(2) Separating the quadrature modulated chroma sig nals into their constituents i .e. Modulated U & V

Components.

(3) Demodulating the modulated U and V signals with the help of a regenerated sub - Carrier.

(4) Regenerating the sub-carrier to enable demodulation of the U & V modulated signals, which are

Transmitted with suppressed carrier an giving the sub carrier in correct phase to the U & V demodulators.

(5) Obtaining the colour difference signals i.e. R -Y, B-Y, and G-Y, signals from the U & V signals.

(6) Obtaining the colour signals i .e. R,G,and B signals from the colour difference signals and the luminance

signals (Y).

These functions are performed by a number of stages/sub -sections in the chroma section as explained below.

The block diagram of chroma section is shown in fig. 2. It is explained as below.

1. Chroma Amplifier: -

This sub-section includes a band pass filter to pass the chroma signals and two amplifiers. I t amplifies the

Chroma signals, which consists of the quadrature modulated U & V signals. The gain of second chrome

amplifier is controlled by the colour control. Also the output of colour killer section is given to the 2 n d

Chroma amplifier to reduce its gain to zero during monochrome (B/W) receptio n.

2. Chroma Delay Line Decoder: -

The U & V signals are transmitted on a single sub -carrier. This is known as quadrature modulation. The

function of chroma Delay-line decoder is to separate the modulated U & V components from the quadrate

modulated signals. This decoder utilizes a chroma delay line for separating the modulated U & V

Components. I t also electronically average the U & V components of successive lines thus removing phase

Distortions, which may take place on long transmission paths.

9

3. U & V Demodulators: -

The U & V signals obtained from the decoder are modulated signals with no carrier (thus these contain

the Sidebands but no carrier). Carrier of correct phase and frequency is required for demodulating these signals.

The U & V demodulators consist of balanced demodulators. These demodulate the modulated U & V signals with

the help of the reference sub -carrier given to them by PAL Switch, phase shift and sub -carrier Generator section.

The demodulated U & V signals obtained from the demodulators are given to the matrix Section.

4. Sub-carrier Generator: -

As the chroma signals are transmitted after suppressing the carrier, reintroduction of the sub -carrier is

Necessary for demodulating these signals. Moreover to obtain the correct colours the regenerated (reference)

Carrier should have the same frequency and phase as that of the sub -carrier at the transmitter.

The sub-carrier generator consists of the sub -carrier oscillator and discriminator (phase detector). The

sub carrier oscillator, which is crystal controlled for high stability, produces oscillations at the desired frequency

(4.43361875 MHz). As even a crystal -controlled oscillator cannot ensure the desired degree of accuracy and

correct phase of the sub-carrier, phase discriminator circuit is used to compare the frequency of the oscillator

with the sub-carrier burst (transmitted on the back -porch of the H. Sync signal) and to synchronize the phase and

frequency of the oscillation with that of this burst.

5. Phase Shift: -

As the quadrate modulation is used for transmitting the chroma signals, the sub -carrier used for

modulating The U signal has a 90 -degree phase shift for demodulating the U signals the phase of the sub -carrier

given to the U demodulator should also have a 90 -degree phase shift. The phase shift stage shifts the phase of the

sub-Carrier given to the U demodulator by 90 degree.

6. Bistable multivibrator and PAL switch: -

As in PAL system the phase of the V signals is reversed on alternate lines. To demodulate these the phase

of the sub-carrier given to the V demodulator should also be reversed on alternate lines. The bistable

Multivibrator along with PAL switch is used to reverse the phase of the sub -carrier oscillations given to the

V demodulator on alternate lines.

The Bistable multivibrator which has two positions is operated by the Indent signal obtained from the

burst Signals. This in turn operates the PAL switch. The PAL switch gives the sub -carrier to the V-demodulator

as it is in one position and reverses its phase in the other position.

7. Colour Killer: -

Colour killer is used to block the chroma amplifier on b lack and white transmission. This is controlled by

the colour burst signal and on black and white transmission, when the colour burst IS absent; it biases the

chroma amplifier to cut -off. Thus it prevents any spurious signals getting through the chr oma section, which

can cause coloured snow on the picture tube screen.

8. Burst-gate: -

8 to 10 cycles of the sub-carrier are transmitted on the back porch of the line sync (H. Sync) signals.

These signals are used for synchronizing the regener ated sub-carrier as well as also for obtaining the Identifying

(indent) signal for the phase reversed V lines.

To separate these signals a part of the CVD signal is given to the burst gate. The burst gate which is

controlled by the line (horizontal) sync pulses allows the signals to pass only during the burst period. Thus it

separates the burst signal.

10

9. Matrix: -

Matrix sub-section consists of amplifier stages along with voltage combining and dividing networks. This

section obtains back the primary colour signals (i.e. and B signals) from the chroma (i.e. & V) signals and the

luminance signals (Y) given to it. (The Y signal is obtained from CVD signal, available from video buffer, by

passing it through sub-carrier trap ).The primary colour signals R,G,B obtained from the matrix section are given

to the output Video Amplifiers circuit.

(4) Horizontal Oscillator and sync separator: -

This section is based on IC TDA 1940F. It consists of Horizontal Oscillator and sync Separator section.

(A) Sync Separator: -

Composite colour signal (CCS) available from Video buffer in Chroma section is given to the sync

separator. It separates the composite sync (Combined H.sync and V.sync) from the CCS signal. The H.Sync

signal is obtained from composite sync by differentiati on. The V sync. is obtained from composite sync signal by

Integration.

The separated H. Sync signal is given to H. Oscillator for synchronizing the phase and the frequency of H.

Oscillator in IC TDA 1940F. The separated V.sync signal is given to V. Oscil lator section (IC TDA 1675A) for

synchronizing the phase and the frequency of V. Oscillator.

(B) Horizontal Oscillator: -

H. Oscillator produces oscillations at the horizontal sweep rate (15625 Hz). The phase and frequency of

this oscillation is maintained in synchronization with the help of H. Sync signal. A discriminator circuit is

used for comparing the phase and frequency of these oscillations with the sync signals and correcting these.

The output of H. Oscillator section is given to the horizontal driver stage in the EHT section.

The muting circuit is also provided in this section. The mute output signal is given to sound section for

putting sound off under no signal condition.

(5) Vertical Oscillator and output: -

This section is based on the IC TDA 1675A. It consists of vertical Oscillator and output section. The

V.Osc. Produces oscillations at the vertical sweep rate. This is further amplified by vertical output section to

drive the vertical deflection coils. The phase and frequency of the V. Oscillator is synchronized by the V.Sync.

Signal, receiving from sync separator. It also provides vertical retrace blanking output signal.

(6B) Output Video Amplifiers section: -

This section consists of three identical stages, one each for the colours R, G, and B. Each of these stages

utilizes a transistor in R-C coupled circuit. These amplifies colour signals at suitable level for driving the

colour picture tube. Their outputs are given to the respectiv e cathodes of the colour picture tube.

(6) Picture Tube section: -

The colour picture tube stage consists of the picture tube along with its accessories i.e. the deflection coil

assembly and colour purity and centring magnets placed on its neck. The col our picture tube displays the R,G and

B signals given to its cathodes in the form of the colour picture with the help of the two sweeps given to the

deflection coil assembly. The colour picture tube used is precision -in-line (PIL) type Full Flat Square Tube

(FFST).

11

(7) Horizontal Driver and EHT Section: -

(A) Horizontal Driver: -

The output voltage obtained from the oscillator is not sufficient to drive the horizontal output stage. A

driver is therefore, used between the oscillator and output stage. This stage is based on a transistor BF393 in

transformer-coupled circuit.

(B) Horizontal Output stage (EHT Stage): -

The EHT stage drives current of saw-tooth waveform through the horizontal deflection coil with the help

of the drive obtained from the driver stage. The following voltages are also obtained from the EHT stage.

(i) DC Voltage of about 25 KV for giving t o the final anode of the picture tube (EHT).

(ii) DC Voltage of about 5 KV for giving to the focusing anode of the Picture tube (Vfc).

(iii) DC Voltages of about 500 volts for giving to the accelerating anode (screen) (Vacc).

(iv) DC voltage of about 150 V Volts for giving to the collectors of the R, G, B output transistors.

(v) DC Voltage of 12V, 25V, for operating the various stages.

(vi) AC voltage of about 6.3 volts for giving to the heater of the picture tube.

The transistor BU208D is used in the EHT stage. An autotransformer known as EHT transformer having

several windings is used with this transistor to obtain the different d.c. Voltages as also to match the output

Impedance of the transistor wi th that of the horizontal deflection coil.

(8) Switch Mode Power Supply section (SMPS): -

The SMPS provides +115V DC and +20V DC supply. As the performance of colour TV receivers depends

Largely on the supply voltage, the supply voltage has been stabilized to maintain it very close to the Nominal

Voltage. 33V DC voltage is also generated from 115V to provide it to Tuner section.

BD508A is used as a switching transistor. SMPS has high efficiency than the Linear Regulated power

Supply. Hence i t is used in colour TV receiver.

(9) Remote Receiver Section: -

This section is based on three ICs. It provides different operational keys to operate the remote colour

T.V.viz. tuning control (+/ -), Volume control (+/ -), Channel selection control (+/-), Store & Function

Control. The main command IC decodes the decoded infrared signals received from the remote transmitter

Section and provides necessary control signals to different sections. The memory IC is used to memories the

Present analog value of Brightness, Contrast, Colour, Volume, Tuning voltage in selected program position.

(10) Remote Transmitter Section: -

This section is based on single IC. It provides decoded infrared signals according to keys pressed to the

Remote receiver section for operating the colour TV from a distance.

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12

PRACTICAL-2

AIM: To study working of Electronic Tuner Section.

Theory:

(A) Tuner: -

The Electronic tuner consists of RF amplifier, local oscillator and mixer. It receives RF input signal

from the antenna via balun at the input socket. I t gives IF output which is gi ven to VIF Section. Tuner AGC

signal is also given to the tuner from VIF section to control its gain. AFT signal is given to tuner from VIF

Section for Automatic fine -tuning. +12.0V is supplied to the tuner pin 4. The desired band of the tuner is

selected by giving

LB, HB and UB Voltage from OPU/RR section for the selection of Band I, Band III and Band UHF respectively.

Also tuning voltage (TU) is given from the OPU/RR for tuning the desired channel in the selected band. C101,

C102, are capacitors for +12V, and AGC signals respectively. C106, C107, C108, are decoupling capacitors for

UB, HB and LB signals respectively.

The RF input comes to RF amplifier via Antenna and Balun transformer. The RF amplifies this signal

with Maximum Signal to Noise ratio. Local Oscill ator generates the sine wave oscillation of the frequency equal

to R.F. Channel frequency (higher side) plus 33.15MHz. This local frequency and R.F. Signal from the RF

amplifier

is heterodyned in mixer stage to produce IF signal.

E.g. for channel no. 5 (174MHz to 181MHz),

Local Osc. Frequency is 181 + 33.15 = 214.15 MHz.

Picture carrier frequency = 174.00 + 1.25 = 175.25 MHz.

Sound carrier frequency = 175.25 + 5.50 = 180.75 MHz.

By hetrodying in mixer, output frequency of mixer are

214.15 MHz - 175.25 = 38.9 MHz (Picture I.F.) and

214.15 MHz - 180.75 = 33.4 MHz (Sound I.F.).

The Composite I.F. signal is produced at the output of tuner.

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19

PRACTICAL-3

AIM: To study working of Video I.F. section.

Theory: -

This section is based on following ICs.

1. Preamplifier IC SL 1430.

2. SAW Filter - BMC389A.

3. V.I.F. IC TDA 3541A.

(1) Preamplifier stage-SL 1430: -

In the V.I.F. stage, SAW Filter is used instead of c onventional coil traps to make alignment simple. But

the SAW filter introduces the 15 dB loss of VIF Signal. To nullify this loss the preamplifier IC201 -SL 1430 is

used. It receives the VIF signal from tuner output at pin 5 Via C203 (1n), L201, and C201 (1 5pf). C201 (15pf)

and C203 (1n) are coupling capacitors. L201 provides input impedance matching at 38.9 MHz frequency. This

enables necessary channel bandwidth for the small signal that is applied to the amplifier. +12V supply to the

IC201 is given at pin 1. C216 (470/16) and C215 (10n) are decoupling capacitors for +12V supply. The amplified

output is obtained from pins 2 and 3 and fed to the SAW filter.

(2) SAW Filter BMC 389A: -

The SAW Filter BMC 389A causes 46 dB attenuation at 31.9 MHz and 40 dB at 40.4 MHz to suppress

channel beat signals. The pass band also suffers attenuation of the order of 15 dB in the filter and thus explains

the need for a preamplifier. The signal feeds at pins 2 and 4 and output becomes available at pins 1 and 5 to be

applied to the IC TDA 3541.

(3) V.I.F. IC-TDA 3541A. : -

It consists of following stages: -

1. Three stages wide band IF amplifier.

2. Synchronous video demodulator (detector).

3. Video Pre-amplifier.

4. AGC detector and noise inverter.

5. White spot inverter.

6. AFT Synchronous demodulator.

7. AFT Output amplifier.

8. Reference amplifier.

The V.I.F. Signal from output pins 1 and 5 of SAW filter is applied at pin 1 and 16 to the IC TDA 3541A

via coupling capacitor C204 (10n). The load resistor R201 (820E) ensure s stability of the TDA 3541A. This input

VIF signal is amplified by the three stage wide band IF amplifier. The maximum overall gain of the amplifier is

58 dB resulting in a typical sensitivity of 100uV at 38.9MHz at the onset of AGC. C205 (10n) connected across

pin 2 and 15 decreases gain at higher frequencies beyond the IF band by progressive negative feedback. The gain

of IF section is AGC controlled over a range of 64 dB in order to take care of the wide range of input signal

levels. The amplified IF signal is given to the synchronous detector. Such a detector is superior to conventional

peak detector circuits in terms of noise -free performance at weak signals, better linearity of the detected output,

lower intermodulation between sound and chroma carrie rs and lower carriers leakage at the output. The reference

signal for the demodulator is generated by the tank circuit L203 and C210 (68pf) in L203.

The composite video signal from the demodulator output is fed to the video preamplifier. This ampl ifies

the signal to the desired level and converts the differential signal to a single ended video output with negative

going sync.

The intercarrier sound signal is tapped from the video output (Pin12) and fed to the SIF section (i.e. IF

Signal). An intercarrier sound trap consisting of L205 and L202 together with R205 (2K2) attenuates sound IF

signal thus preventing its passage to video, chroma and other circuits.

21

In order to prevent false AGC action and to limit the video signal amplitude during presence of noise, a

noise inverter circuit is incorporated into the video amplifier stage. After noise inversion, the video signal is

applied to the AGC circuit to derive required AGC voltages. The voltage across C206 (22n) at pin 14 indirectly

controls current through the IF amplifiers and controls the IF stage gain. When the sync tip level of the video

signal exceeds the reference level set in the AGC comparator, the capacitor discharges there by reducing the

AGC voltage at pin 14. This in turn reduces current through the IF amplifiers, thus reducing the gain. The AGC

control Voltage at pin 14 is compared with voltage at pin 3 to generate delayed AGC voltage (Tune r AGC)

required for the tuner at pin 4. The amount of delay can be adjusted by varying voltage at pin 3 by preset Pr201

(10K preset). For VCR operation pin 14 is grounded to turnoff the video output emitter follower. This presents a

high impedance at pin 12 and avoids overloading of the external video signal.

To obtain optimum performance from the synchronous demodulator it is essential that the reference IF is

maintained at the correct value. For this, the AFT corrects any effect of slight mist uning of the reference tuned

circuit. The AFT circuit generates current which varies in proportion to any deviation for the nominal frequency

of the IF input to the IC. This current is converted into an AFT control voltage at pins 5 and 6 from there fed to

the AFT pin of the tuner. The AFT signal can be switched OFF by shorting AFT SW.

Composite Video signal is also available as Video Out signal at Video out socket.

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23

PRACTICAL-4

AIM: To study working of Sound I.F. Section.

Theory: -

The IC CA 1190 is a complete sound IC. It includes a multistage If amplifier - limiter, FM detector, DC

volume control and an audio power amplifier. A regulated power supply is also provided for feeding various

stages in the IC. This reduces unwan ted coupling between the stages to a minimum.

The SIF signal from the VIF IC TDA 3541A-pin 12 is fed to the pin 1 of CA 1190 after suitable impedance

matching between the output of the VIF Section and the input of CA1190. This IF signal after suf ficient

amplification and limiting is available at pin 6 for detection. After detection detected audio signal is amplified

by A.F. Power amplifier to deliver the required power to the loudspeaker.

The S.I.F. signal is fed to the pin 1 of IC CA 1 190 via current limiting resistor R308 (330E) and Ceramic

filter L301 (SFE5.5Mb). Ceramic filter provides filtering of unwanted video frequencies present in the input

signal. It offers a 3 dB bandwidth of about 150 KHz to SIF signal. C301 (47n) provides fi ltering of high

frequency noise and low frequency ripple of voltage at pin 2 i.e. decoupling. R301 (4E7) and C317 (47n)

provides decoupling to SIF amplifier. Pin 4,5 and 12,13 are heatsink tabs which are grounded. The SIF signal

after sufficient amplificat ion and limiting is available at pin 6 for detection. C316 (10pf) and C320 (68pf)

(internal in L302) and L302 provides F.M. demodulation by forming a differential peak detector. After detection,

the detected audio signal is amplified by A.F. power amplifi er to deliver the required power to the LS at pin 11.

C302 (10/16) provides decoupling for voltage at pin 8. The DC volume control is provided in the IC301. The DC

voltage at pin 8 decides the audio gain i.e. works as volume control. Here volume control si gnal from OPU/RR

section is given to pin 8 through current limiting resistor R309 (2K2). R306 (22K), R304 (47E) and C311

(100/16) decide the gain of audio amplifier by providing -Ve feedback at pin 9. C313 (100pf) and C314 (1n)

provide high frequency compenstation for AC signal. C307 (4n7) provides necessary deemphasis. R305 (1E) and

C315 (0.22u) are used for loudspeaker impeance compensation at higher frequency at pin 11. Also C312 (470/16)

connected to pin 11 couples the output signal to LS. The muting si gnal applied at pin 2 from H. Osc. Section

keeps LS off during no signal condition or while channel selection. This IC provides 5.0 watts output.

The external Audio input can be connected at Audio IN socket. This signal is connected at pin 7 of IC

CA1190 through limiting coupling resistor and capacitor ( 1K, 47K and 2.2/16). The internal audio is also

available at Audio Out socket through IC pin 16 via coupling resistor 1K and capacitor 10n for audio recording.

26

PRACTICAL-5

AIM: To study working of Horizontal oscillator section.

Theory :

This section is based on IC TDA 1940F. It contains following stages as shown.

(1) Sync Separatior.

(2) Horizontal oscillator

(3) Muting facility

(4) Sandcastle pulse generator

(5) VCR Operation

(6) Start Circuit.

(1) Sync Separator: -

The Horizontal Sync and Vertical Sync pulses are separated by two independent differential sync

separators. This is done by setting two different clamp levels independent of Sync pulse amplitude. The

separation level of Horizontal sync separation is set at about 50% of sync pulse amplitude. Similarly, separation

level for frame sync is chosen to the blanking level. For this, different D.C. Levels are chosen at pin 8, 10 and 12

of IC TDA 1940F through R621 (27K) and R618 (47K), which provide D.C. Supply to the input circuits of the

two sync separators. The negative going composite colour signal (CCS) is applied via R603 (2K2) at pin 11 t hat

distributes it to the sync separators and noise getting circuit. The noise suppressor is activated at predetermined

voltage level to block passage of any spiked noise pulses. The separated horizontal sync pulses are fed to the

first phase loop comparator, which is designed to synchronize the phase and frequency of the horizontal

oscillator. However, the composite sync is applied via pin 9 to the integrator circuit R606 (5K6) and C603

(47n/100) to provide V.Sync pulses to be fed to the V.Osc. IC TDA 1675 .

(2) Horizontal Oscillator and Frequency Control: -

The Voltage controlled H. Oscillator produces a saw tooth output at 15625 Hz. The frequency is

determined by the low-loss styroflex Capacitor C605 (10n st) connected at pin 15. The precise control of ph ase

and frequency of this oscillator is affected through two -phase lock loop circuits and a coincidence detector. The

H. Oscillator synchronization is obtained by the first phase comparator whose pull -in-range and control slope is

externally adjusted via R-C networks connected at pin 6, 13 and 16. The preset Pr601 is H.hold .pn36 frequency

control. The second phase control comparator compares the line fly back pulses applied at pin 3 (from EHT) via

resistor R602 (68K) with the internally generated saw tooth output from the oscillator and keeps phase of the

reproduced picture at its correct position. The picture phase position can be adjusted externally by preset Pr602

through which D.C. voltage is fed to the comparator at pin 17.

(3) VCR (AV) Operation: -

The coincidence detector compares the line drive pulses (formed by the output pulse shaper) with the

horizontal sync pulses to ensure that drive output from pin 2 is in correct phase relationship with the period of

horizontal fly back pulses. In addition the coincidence detector controls feeding of H.Sync pulses to the first

comparator via a gate pulse circuit. The external components connected at pin 5 determine time constant for

optimum operation of the coincidence detector and through that of the phase comparators. However, for non-

standard, signals like from a VCR, a different time -constant is necessary for a stable picture. For this, the

program channel AV is selected. When this channel selected IC in OPU/RR section provides + 12V dc at VCRSW signal which is applied at pin 5 through R 601 (2K7), C615 (4n7), R631 (6K8) and D601( 1N4148). This

+12Vdc forward biases diode D601 (1N 4148) to connect R 601 (2K7), C615 (4n7) and R631 (6K8) in parallel to

reduce the time constant.

(4) Sandcastle Pulse Generation: -

The sandcastle pulse generator combines vertical fly back pulse (V.BLK) and H.Oscillator output pulses to

form sandcastle pulses that are fed from pin 4 to chroma IC i.e. CD section.

28

(5) Sound Muting: -

The coincidence detector output is also fed to the muting circuit whose output is connected from pin 7 to

the base of transistor Q601 (BC 158B) via R622 (39K). In the absence of any TV signal there is no output to the

muting circuit. This causes drop in voltage at pin 7 that is enough to conduct to turn on Q601. The resulting

collector current provide about 6V on pin 2 of sound IC CA1190 which turns of volume. Thus with no RF input

or during channel selection there is no noise ou tput (i.e. no sound of snow) from the loudspeaker.

(6) Start Circuit: -

When TV set is switched ON, +18V D.C. supply is given to the collector of start transistor Q602 (BC

147B). The emitter is at zero Volts. Hence Q602 conducts and some voltage is available at the emitter i.e. at IC

supply pin 14. Hence some EHT will be generated and +12V will be available from the EHT. So the emitter is

now at +12V DC and Q602 becomes off. This, not only means less power drawn from the mains but

interdependence of Horizontal and vertical oscillator voltages helps in maintaining aspect ratio at its correct

value.

*******************

33

PRACTICAL-6

AIM: To study working of Vertical oscillator section.

Theory: -

This Section is based on the IC TDA 1675A. It contains following stages: -

(1) Vertical Oscillator

(2) Ramp generator

(3) Buffer

(4) Guard Circuit

(5) V. Sync Circuit

(6) V. Blanking

(7) V. Preamplifier

(8) V. Output and protection.

The V.Sync pulses are applied to pin 5 through potential divider circuit R426 (10K) and R425 (4K7). The

V.oscillator frequency is determined by V. Hold Preset Pr403 (4K7 Pr), resistors R401 (12K), R409 (1K)

connected between pins 4 and 6 and capacitor C401 (0.15u) across pin 3 and 4. The saw tooth frequency at 50Hz

is adjusted by V. Hold preset. The amplitude of this saw tooth output is set by a R423 (270K) and V.Height

preset Pr401 (220K pr), which determine bias voltage on the oscillator ci rcuit.

The pins 9 and 10 are for ramp generator and buffer amplifier. The dc supply for charging ramp capacitor

C411 (0.1u) is obtained from EHT (V.stab signal) through resistor divider network R422 (10K) and R421 (390K)

and fed to pin 9 via R418 (1M5). Any beam current variations affect dc voltage obtained from EHT and hence

width of the raster. This also changes the height of the raster because dc supply to the ramp generator is

proportional to the focus anode voltage. Thus, a fixed aspect ratio i s maintained despite voltage fluctuations at

the mains or EHT ckt. A parabolic voltage is developed across C412 (0.1u) and fed back to the ramp circuit to

obtain linear deflection. The preset Pr402 (100K pr) connected to pin 10 via R416 (56K) is varied to control

amplitude of feedback voltage for a linear deflection of the beam i.e. Pr402 works a V.linearity control.

The output stage receives drive from the preamplifier and feeds necessary current from pin 1 (V1) to the V.

deflecting coils. To prevent any shift in the raster position on the screen, only AC current is allowed to flow

through the field coils by inserting coupling capacitor C406 (1000u/25) in series. The output circuit is completed

to pin 8 (ground) of .pn41

The IC through the small feed back resistance R413 (1E5) that is grounded. The overall linearity and

stabilization of operation is obtained by both ac and dc feedbacks. The small ac voltage that develops across

R413 on current flow is shaped by the network consisting of R414 (270E), C407 (47/25) and R415 (1K) and fed

at pin 12, which is connected to the input circuit of preamplifier. Similarly a small dc voltage that occurs across

the coupling capacitor C406 is feedback at pin 12 via R412 (2k2).

The resistance R407 (470E) that shunts the deflection coils is to prevent any high frequency oscillations that

may occur during retrace. The capacitor C402 (0.22/100) and R403 (2E7) form a high frequency shunt path from

output pin 1 to ground agains t any instability of operation in the deflection circuit. The resistor divider network

R408 (1K2) and R411 (1K2) from +25V dc supply connects a fixed dc voltage at the lower end of vertical coils.

The vertical position can be changed by altering these resi stors. The +25V dc supply from the EHT is given to

pin 14 via R405 (10E,1/2W) and via diode D401 (1N 4002) at pin 2 and through dropping resistor R406 (3K3) to

pin 13. The voltage regulator from pin 14 distributes to supply to various stages in the IC. The output amplifier

receives dc supply from diode D401 (1N 4002) where capacitor C405 (47/25) boost up voltage to be available

during retrace intervals. I t is necessary to apply a large dc voltage at the beginning of retrace to counter the back

emf voltage induced in the coils because it is only then that a smooth and fast retrace becomes possible. The

capacitor C404 (0.1u) is for high frequency bypass when retrace occurs. V. Retrace blanking (V.BLK) pulses are

available at pin 13 and fed to pin 18 of TDA 194 0F for forming sandcastle pulses.

*******************

35

PRACTICAL-7

AIM: To study working of Colour Decoder Section.

Theory: -

This section is based on the IC TDA 3561A.

This IC consists of following sections: -

1. Chroma amplifier

2. Automatic colour control (ACC)

3. Colour killer

4. Gated burst amplifier

5. Burst phase discriminator

6. Subcarrier reference oscillator

7. PAL Switch

8. Burst phase identification

9. Phase shift

10. Pulse shaper

11. U & V demodulator

12. RGB matrix

13. Luminance signal processing (external to IC)

14. PAL delay line (external to IC)

15. Beam current limiting (external)

16. Chorma band pass amplifier (external to IC)

17. Video buffer (external to IC)

18. External data insertion.

19. Output signal clamping and blanking.

The composite video signal (CVD) from the IC TDA 3541A (VIF section) is given to the video buffer

transistor Q860 (BC 147B). The output signal is available at the emitter of Q860. From the emitter this

composite colour signal (CCS) is given to thr ee paths.

1. Directly to horizontal osc. and sync separator section for separating H.sync, V.sync and colour burst.

2. To separate chroma signal from CCS and to give it to IC pin 3 after passing it to suitable band pass

traps.

3. To obtain luminance signal (Y) to give it to IC pin 10 after passing it through colour

Sub carrier trap and luma delay line.

(A) Chroma Signal Path:

The CCS signal available at the emitter of Q860 is given to the chroma band -pass trap consisting of R852

(4K7), C851 (15pf), R853 (2K2), C853 (22pf) and L853. After proper chroma band shaping it is given to the pin

3 of IC-TDA3561 through coupling capacitor -C857 (22nDC).

(B) Luminance Signal Path:

The CCS signal available at the emitter of Q860 is given to the RC network consisting of R860 (270E),

C861 (220pf), R862 (330E) and R863 (270E) for proper attenuation and band shaping to provide only Y signal.

C860 (27pf) and L860 provides trap for 4.43 MHz chroma subcarrier signal to prevent it t o reaching Luminance

signal input-pin 10 of IC. The Luminance signal delay is required as chroma signal passes through complex

circuit and reaches later than Y signal, hence Y signal is delayed so as to reach both luminance and chroma

signals at the same instance at the modulating electrodes of the picture tube. Thus Y delay is necessary to avoid

blurring of colours at the edges of various objects in the reproduced picture. Hence Y delay line DL1 is used to

provide delay of @330ns to Y signal.

35

The colour, brightness and contrast voltages are given from OPU/RR section to potential dividers across the

common +12V supply with each supplying an adjustable voltage to its associated pins 6,11 and 7 respectively.

Also nominal black level preset Pr802 is connected at pin 11. The output from the chroma amplifier appears on

pin 28 from where it is connected to the externally mounted PAL delay line and its associated components. Pr601

is colour amplitude control. L880 is chroma phase alignment coil. The U & V signals (R -Y and B-Y) that become

available at the output of delay line, adder and subtractor circuitry are fed back into the IC via pins 21 and 22

and from there to the B-Y and R-Y demodulators in the IC. The Chroma delay line seperates B -Y and R-Y

modulated signals from combined chroma signal. The 4.43 MHz reference oscillator signal required by the two

modulators is derived by an external crystal (Xtal X875 -8.86 MHz) connected across pins 25 and 26. The 8.86

MHz signal is inverted to obtain another 8.86MHz source 180 degree out of phase with it . Both the signals are

then divided by a factor of two to obtain two independent outputs at 4.43 MHz at 90 degree phase shift with each

other.

The IC pin details are as under.

Pin 1 - +12V supply

C898 (100/16) and C856 (22n) are decoupling capacitors for +12V supply.

Pin 2 - Control voltage for identification-

The H/2 identification or detector circuit. C896 (0.33u) is used to pr oduce this control voltage.

Pin 3 - Chroma input signal -

Pin 4 - Reference Voltage ACC Detector -

A decoupling capacitor C895 (0.33) is provided at this pin to produce reference ACC voltage.

Pin 5 - Control Voltage ACC -

The ACC is obtained by synchronous detection of the burst followed by a peak detector. For good -noise

Immunity C894 (2.2/16) is connected between pin 4 and 5.

Pin 6 - Colour (saturation) control -

R921 (39K), R920 (10K) and R922 (39K) is potential divider to limit the control voltage range between

2 to 4V. C920 (1/16) is for decoupling. When this pin is connected to the +12V, through colour SW, the

colourkiller circuit is over -ruled so that colour signal is visible on the screen for adjustment of C875.

Pin 7 - Contrast Control

R916 (390k), R917 (680K), R915 (120K) is potential divider to limit the control voltage range from 2 to

4V. The output signal is suppressed when control voltage is 1V or less. If the signal surpasses the level of 9V,

the peak white (beam current) limiter circuit becomes active and reduces the output signal by discharging C915

(1/16) via an internal current sink. Q900 (BC147B) works as beam current limiting transistor (in EHT section).

When beam stabilization signal ( which depend on EHT output as explained in EHT section) increases certain

level, the collector voltage of Q900 increases beyond 9V, which is given to the IC Pin 7 for reducing the output

for preventing PT Cathodes from destroying.

Pin 8 - Sandcastle and Field Blanking Input:

The Sandcastle and field blanking input is given to this pin, from pin 4 of IC TDA 1940F in

H.Osc.section. A gate pulse separator circuit inside the Ic separates and routes burst and Blanking Pulses to

corresponding circuits. If the amplitude of sandcastle pulse is between 2V to 6.5V it indicates that transmission

is black and white. Then no RGB signals are available at 12, 14 and 16. However, when the pulse amplitude

exceeds 7.5V the burst gate and clamping circuits are activ ated. The higher part of sandcastle pulse should

start just after the sync pulse to prevent clamping of video signal on Sync pulses.

Pin 9 - Video - Data switching:

In normal operation this pin is connected to ground via R892 (1K). During ON Scree n display signal

the insertion circuit is activated through this pin by an input pulse of magnitude between 1 and 2V of OSD. In

this condition, the internal RGB signals are switched off and the inserted signals (OSD) are applied to the

output amplifier.

Pin 10 - Luminance Signal Input:

It must have amplitude between 0.45V To 5V (peak to peak) at nominal contrast.

42

Pin 11 - Brightness Control :

The black level clamp of RGB outputs can be met by the voltages on this pin 11. R911 (68K), R910 (3K3),

R912 (27K) is potential divider to limit the brightness voltage between 1 to 2.5V. C9 (1/16) is the decoupling

capacitor. Pr802 (10K pr) i s nominal black level control preset.

Pin 12 - Red output signal (VDR)

Pin 14 - Green output signal (VDG)

Pin 16 - Blue output Signal (VDB)

Pin 13 - Input for external R input signal.

Pin 15 - Input for external G input signal.

Pin 17 - Input for external B input signal.

These pins 13,15,17 are left open, as they are not used.

Pin 18 - Black level clamp for B signal.

C891 (0.1u) is black level clamp capacitor for Red colour.

Pin 19 - Black level clamp for G signal.

C892 (0.1u) is black level clamp capacitor for Green colour.

Pin 20 - Black level clamp for R signal.

C893 (0.1u) is black level clamp capacitor for Blue colour.

Pin 21 & 22 - Inputs (B-Y) and (R-Y) demodulators

The voltage level of these signals is automatically fixed to the required level by means of burst phase

detector and ACC generators which are connected to pins 21 and 22. R884 (220E), R885 (220E) are biasing

resistors at pin 21 and 22. C883 (22n) is coupling capacitors to couple chroma output signals from pin 28 to

chroma delay line.

Pin 23 & 24 - Burst phase detector outputs :

At these pins the output of burst detector (inside the IC) is filtered by C877 (0.1u). The filter circuit has

Suitable time constant for adequate catching. R876 (1K) and C 876 (22/16) provide this time constant.

Pin 25 & 26 - Reference subcarrier Oscillator:

The frequency of the reference subcarrier oscillator is adjusted by variable capacitor C87 5 that is in series

with 8.86 MHz crystal connected between pins 25 and 26 of the oscillator circuit.

Pin 27 - Ground Pin:

Pin 28 - Output of chroma Amplifier:

Both burst and chroma signals are available at this pin. It is fed to the PAL -delay line circuit to obtain U

and V signal. Pr901 (470E Pr) is colour amplitude control preset. L880 is chroma phase Coil. L881 is chroma

input coil. C881 (22n) is chroma -coupling capacitor to chroma delay line.

Emitter bias

The transistor Q930 (BC147B) is a constant current source, which develops emitter bias (E.Bias) at R931

(68E) to provide it to VDA section. R932 (1K), R933 (330E) are i ts biasing resistors. R930 (180E) is the

collector load resistor.

******************

43

PRACTICAL-8

AIM: To study working of S.M.P.S. Section.

Theory: -

The main function of this section is to provide isolated + 115V and +18V DC supply from 230V AC mains.

The S.M.P.S. section consists of five processes.

1. Generation of +330V DC.

2. Switching Action.

3. Controlling Action.

4. Starting of switching Action.

5. Output Voltage rectification

(1) Generation of +330V DC: -

The ac mains voltage is applied from remote receiver section through relay and protection fuse F801 (2A).

The capacitors C801 (0.1u), C802 (0.1u), bifilar inductor M801 (EMI Filter) form a - Filter configuration to prevent mains side interference entering the SMPS circuit. I t also prevents the pollution of ac mains by spiked

pulses generated in the switching transistor Q804 (BU 508A). This EMI consists of two small inductors wound on

the same core and mutually coupled in such a direction that mag netic field produced by the each cancel out. The

ac main is also fed to degaussing coils through PTC thermistor for demagnetizing picture tube structure every

time the receiver is switched ON.

The mains supply is rectified by a bridge circuit forme d by diodes D801 to D804 (1N4007) and a dc voltage

about +330V is developed across the filter capacitor C807 (100u/400). C803 to C806 (4n7/400) are high

frequency noise bypass capacitors for D801 to D804. The fusible resistor R802 (3E3/5W) limits in -rush current

to a safe value at the time of switching ON.

(2) Switching Action: -

The switching transistor Q804 (BU 508A) and SMPS transformer M802 constitute the blocking oscillator

that is set to operate at a frequency close to 15 KHz. The positive feedback for sustained oscillations is obtained

by rectifying the voltage induced across the winding (9 -10). The feedback current complete its path from pin 9

via base emitter junction of Q804, R816 (1E, 1/2W), R817 (22E,1/2W) and Diode D808 (BA159) to other end

(pin 10) of the winding. The resistor R817 (22E, 1/2W) and R816 (1E, 2W) limit the base current to a safe

maximum value. The transistor Q804 passes a rising current through winding (1 -7) from +330V supply given

through fuse F802 (1A fuse) during its ON period. The current completes its path from +330V (+ve terminal) to SMPS ground (-Ve terminal) via fuse F802 (1A), drive winding (1 -7), collector to emitter of Q804, R816 and

R815 (2E2, 1/2W). The resistor R815 produces a small -ve feedback to suppress collector current peaks.

Similarly, series network C812 (1n5/2KV) and R818 ( 33E, 5W) is to quench any high voltage peaks across the

switching transistor. The energy stored in the primary winding (1 -7), when Q804 conducts, is transferred to load

circuits through secondary windings (6 -5) and (6-4). The transfer occurs during OFF periods of Q804 when polarity of induced voltages is +ve at upper ends of these windings.

(3) Controlling Action : -

The regulation is obtained by controlling ON period of Q804 by removing base drive to it for varying intervals. This is done by closing the PNPN Switch formed by transistor Q802 (BC158B) and Q803 (BC147B)

with signals from the load sensing winding (11 -12). Normally the base of Q802 is held at +Ve potential with

reference to its collector by a dc voltage derived from 30V supply line an d D805 (8.2V) zener. The control

(error) signal is obtained from the load sensing winding (11 -12) by rectifying it with diode D807 (BA159) and

C809 (10/63). The +ve voltage is applied to the base of error amplifier transistor Q801 (BC147B) via R806

(6K8), Preset Pr801 (1Kpr) and R807 (2K7). The zener D805 (8.2v Zener) passes current through R809 (8K2) to

develop a fixed voltage 8.2V across it. It serves as reference voltage to the error amplifier. The base to emitter

bias for Q801 is set by varying Pr801 to such a value that it passes only a small collector current under normal

output load conditions. The ensuing collector current develops only a small +ve voltage across R808 (1K8). This

44

voltage is given to the base of Q802 (BC158B) via R812 (10K) and R813 ( 6K8) potential divider. Hence Q802 is

OFF. Hence Q803 is also OFF and feedback is continuously applied to the base of Q804 from the drive winding

(9-10).

During fluctuations in load or line supply voltage, the error voltage changes and this affect s base drive to

the error amplifier Q801 with excess energy in the transformer windings, the error signal increases, and Q801

drives more and collector current increases hence its collector voltage reduces. Hence Q803 and Q802 becomes

ON i.e. there is a short across between the emitter of Q803 and Q802 and C811 +ve terminal. The capacitor C811

which was earlier charged by diode D811 (BA159) to the voltage across winding (9 -10), now discharges to pass

current through Q802 and Q803. The sudden discharge of C8 11 causes two things. The voltage at emitter of Q802

drops to near zero and Q802 and Q033 becomes open. With near short across C811, the feedback winding is

almost short circuited via R815, R808 and R817 thereby removing base drive to Q801. This reduces O N time of the switching transistor to counteract excess energy stored in the windings. Such a situation can continue for

several oscillator cycles to balance energy transfer from primary to secondary. The error voltage continuously

monitors output voltage to provide excellent voltage regulation on the load side.

(4) Start of switching Action: -

On turning on the set, switching action of Q804 starts with base bias supplied via +330V supply to the base

of Q804 via R819 (330K, 1/2W) when there is no f eedback voltage of its emitter. While frequency of switching

gradually picks up with feedback from drive winding (9 -10) the base bias given bo +330V is stopped.

(5) Output Voltage Rectification: -

+115V and +18V D.C. Supply are obtained by rectifying output pulses available across secondary winding

(5-6 and 4-6) by D809 (BA159) & C816 (100/250) and D810 (BA159) & C817 (1000/25) respectively. +33V is

also derived from +115V supply by R720 (12K, 2W) and C709 (100/40). C709 IS decoupling/filter capacitor for

+33V. This +33V is given to RR section for tuner.

(6) Prevention of Interference: -

The input circuit to the a.c. mains is suitably designed to filter out high harmonic components and prevent

passage of interfering pulses either way. To quench high voltage pulse that may damage Q804 a network consists

of C812 and R818 is connected between its collector and emitter. This also prevents any frequency oscillations

by dissipating excess energy in R818. Since the SMPS frequency is not synchronized with the line oscillator,

careful shielding of power supply components is necessary.

******************

45

PRACTICAL-9

AIM: To study working of Colour Picture tube Section.

Theory: -

The picture consists of three gun Red, Blue and Green. The R, G, B outputs from VDA is applied to

respective cathode of the gun.

i.e. B output to blue cathode BK (pin 11)

G output to Green cathode GK (Pin 6)

R output to Red cathode RK (Pin 8)

Pin 9 and 10 are the filament pins. Filament Voltage 6.3V ac from EH T Section is applied to pin 10. pin 9 is

grounded for filament voltage return path.

Pin 5 is control grid (G1). The Horizontal blanking pulses (H. BLK) obtained from the EHT section are

applied to pin 5 through current limiting resistor R2 (1K). C 5 (100pf) is high frequency bypass capacitor for H.

BLK signal.

Pin 7 is the screen grid (i.e. Accelerating grid -G2). Accelerating Voltage V.ACC about (100V to 300V) is

applied from EHT Section through R3 (1K) and C1 (33n/630V). R3 is current limit ing and C1 is high frequency

bypass capacitor for V.acc.

Pin 1 is the focus grid (G3). About 5.9 KV Voltage (VFC) is given to the focus grid from EHT Section for

focusing purpose. The deflection yoke is situated at the neck of picture tube along wi th purity and convergence

magnets.

About 25KV EHT Voltage is supplied at the EHT connection (Final Anode of PT) from the EHT Section.

The Vertical and Horizontal sweep is applied to V. deflection and H. deflection coil from V. Osc. and EHT

Section respectively for deflection of Beam.

H1-H2 is H. deflection coils and V1 -V2 is V. deflection coils. Aquadag coating of the colour picture tube is

earthed to high voltage ground of EHT (i.e. EHT pin 5). C5 is also connected to High Voltage Ground i .e. control

grid voltage is at high voltage reference. Spark gaps are used at each pin of tube to bypass high voltage sparking

etc.

******************

60

PRACTICAL-10

Aim: To measure Test Point Voltages for different sections.

Readings: -

All voltage are DC voltage measured by DMM except mentioned.

(1) Main Voltages: -

1. +115V Output from SMPS

2. +18 V Output from SMPS

3. +12 V Output from EHT

4. +25 V Output from EHT

5. +150V Output from EHT

7. Q714 (BF393) Collector + 60V.

8. +330V DC at Fuse F802 with reference to bridge rectifier ground

(2) Voltages of different sections: - 1. Tuner section: -

1. AFT 5.2

2. AFT SW 0.0 When AFT SW is ON.

3. UB 10.6 if Band UHF selected.

4. LB 10.6 if Band I Selected.

5. TU 0 to 33.0 depending upon the channel selected.

6. HB 10.6 if Band III Selected.

7. TU AGC 2.7 to 8.2

8. +12V 12.1

9. IF O/P 0.20

2. 2. V.I.F. Section: - (A) IC SL 1430

Pin

1. +12V supply 12.1

2. IF O/P 5.7

3. IF O/P 5.8

4. X X

5. IF I/P 3.0

6. Ground 0.0

7. X X

8. X X

(B) IC TDA 3541A/2541A

1. IF Input 4.8

2. Decoupling 4.8

3. Tuner AGC starts 1.0

4. Tuner AGC 1.3

5. AFT Output 5.9

6. AFT Switch 0.0

7. AFT Coil 3.9

8. VD coil 7.9

9. VD Coil 7.9

10. AFT coil 3.9

11. +12V Supply 12.1

12. CVD O/P 4.0

13. Ground 0.0

14. IF AGC/ VCR switch 6.5

61

15. Decoupling 4.8

16. IF Input 4.8

(3) SIF Section: -

(A) IC CA 1190

1. SIF Input 3.2

2. SIF Input 3.2

3. Decoupling 3.1

4. HS Tab X

5. HS Tab X

6. FM detection 2.5

7. FM detection 2.5

8. Volume control 3.5 (1.8 at full volume)

9. Gain 9.4

10. Fre. Compensation 0.7

11. Audio output 9.3

12. HS Tab X

13. HS Tab X

14. +18V Supply 18.4

15. Feed back 9.4

16. Deemphasis 9.4

(5) H.Oscillator section: -

(A) IC TDA 1940F

1. Ground 0.0

2. H.O/P 1.3

3. HFB -0.2

4. SCP 1.7

5. VCR SW 1.9

6. - 0.0

7. Mute 11.5

8. - 5.8

9. V.Sync 1.5

10. - 4.5

11. CCS 3.8

12. - 6.6

13. - 5.0

14. +12V supply 11.1

15. H. Osc. Fre. 5.4

16. - 5.6

17. H.position 5.0

18. V.BLK 0.2

(B) Mute Transistor: -

1. Q601 Collector 0.1

Base 11.5

Emitter 11.5

2. Start Transistor

Q602 Collector 18.5

Base 10.1

Emitter 11.5

(6) V.osc. Section: -

(A) TDA 1675A

1. V1 13.8

2. - 24.5

3. V.osc. Fre. 3.4

4. V.osc. Fre. 0.5

62

5. V.Sync 0.4

6. V.osc. Fre. 0.5

7. Height 6.8

8. Ground 0.0

9. V.Stab 3.5

10. V. Linearity 4.5

11. - 4.3

12. - 4.2

13. V.BLK 1.1

14. +25V Supply 24.5

15. - 1.6

6A. Chroma Section: -

(A) IC TDA 3561 A

Pin

1. +12V supply 12.0

2. Indent control Voltage 3.2

3. Chroma Input 2.6

4. Reference ACC 4.7

5. Control Voltage ACC 3.8

6. Colour control 1.8 to 4.0

7. Contrast control 1.8 to 4.0

8. SCP 1.7

9. Video data SW 0.1

10. Luminance Y signal input 1.8

11. Brightness control 1.8 to 4.0

12. Red output 4.0

13. Red ex-input 5.6

14. Green output 4.0

15. Green ex-input 5.6

16. Blue output 4.0

17. Blue ex-input 5.6

18. Black level clamp for Blue 10.5

19. Black level clamp for 10.5

Green

20. Black level Clamp for Red 10.5

21. B-Y 2.6

22. R-Y 2.6

23. Burst phase detector 9.8

24. Burst Phase detector 9.8

25. Subcarrier Osc. 10.3

26. Subcarrier Osc. 2.1

27. Ground 0.0

28. Amplified chroma output 8.0

(B) Transistors

1. Video buffer Q860 Collector 12.1V

(BC 547B) Base 4.0V

Emitter 3.4V

2. Emitter Bias Collector 9.5V

Q930 (BC 547B) Base 3.1V

Emitter 2.4V

(6B) VDA Section: - (A) Transistors

1. Red O/P transistor Collector 63.0

Q 11 Base 3.0

63

Emitter 2.4

2. Green O/P transistor Collector 64.0

Q 21 Base 3.0

Emitter 2.4

3. Blue O/P transistor Collector 60.5

Q 31 Base 3.0

Emitter 2.4

(7) EHT Section: -

1. +115V Supply Input 115.0

2. +18 V Supply Input 18.5

3. +12 V Output 12.4

4. +25 V Output 24.5

5. +150V Output 152.0

6. F1 Output 6.0 V AC

7. F2 Output 0.0

8. HFB Output 17V AC

9. H.BLK Output 7.7V AC

10. HVR Output -22.0

11. Beam stab output 0.7

12. Vacc (g2) output 10 0.0

13. H. Drive 1.5

14. BU 208D Collector 250V AC To be measured by Analog Multimeter only

15. BU 208D Base 0.6V AC To be measured by Analog Multimeter only

16. BF 393 Collector 65V DC To be measured by Analog Multimeter only

(A) Transistors

1. Beam Current limit Collector 2.3V

Q900 (BC 147B) Base 0.0V

Emitter 0.7V

(8) SMPS Section: -

(A) Transistors All voltages to be measured with respect to pin 11 of SMPS Xmer i.e cathode of Diode D805 (8.2V Zener diode)

Q801 BC 147B Collector 11.4

Base 9.2

Emitter 8.5


Base 4.9

Emitter 1.1


Base 0.1

Emitter 0.0

Q804 BU 508A Collector 340 VAC To be measured by Analog Multimeter only

Base -2.2

Emitter 0.2

(9) Picture Tube Section: -

Pin

1. Focus grid g3 5.0 KV DC

2. X X X

3. X X X

4. X X X

5. Control grid g1 7.7 V AC

6. Green Cathode GK 64

7. Screen Grid g2 100

8. Red cathode RK 63

9. Filament 1 f1 6.0V AC

64

10. Filament 2 f2 0.0

11. Blue Cathode BK 60

Main Test Point Signals

1. IF I/P 0.2

2. CVD 4.0

3. SIF 4.0

4. AFT 5.9

5. TU AGC 1.1 to 8.2

6. LS 6.5 VAC with full volume.

7. H.O/P 1.5

8. V.Sync 1.1

9. HFB 18V AC

10. CCS 3.8

11. SCP 1.7

12. V1 14.0

13. V2 13.5

14. V BLK 1.1

15. VDR 4.0

16. VDB 4.0

17. VDG 4.0

18. E.BIAS 2.4

19. R 63.0

20. G 64.0

21. B 60.0

****************

79

PRACTICAL-11

Aim: - To demonstrate and understand the faults of a Colour TV Receiver.

Faults can be created either:

(1) by removing jumpers connecting the different sections.

(2) by removing or shorting particular component.

(3) by misadjusting internal or external or external controls.

Note: - Remember that, every time switch off the trainer when removing or connecting any jumper or

Component. Readjust any control /preset/coil if it was disturbed, to see the fault as per alignment

Method given in

Procedure: - Any one fault can be created by many ways.

Following faults can be demonstrated by removing ANY of the given jumpers.

Jumpers to be disconnected. Fault

(A). S.M.P.S. Section: -

(1) 1. +115V and +18V supply No Raster, No Picture, No Sound

(2) 1. +115V jumper No Picture, No Raster, Sound O.K.

(3) 1. Reduce +115V supply by Less Height and Width.

Pr801 by rotating it

Anticlockwise

(4) 1. Increase +115V supply More Height, Width and brightness

By rotating preset

Pr801 clockwise

(5) 1. +33V jumper No operation of remote receiver

(B). Vertical Section: -

(6) 1. V1 jumper Straight H.Line

2. +25 V jumper

(7) 1. V2 jumper Curved H.Line

(8) 1. Rotate Preset Pr401. Less or more Height

(9) 1. Rotate Pr402 Vertical Linearity improper

(10) 1. V.Lin. Jumper Vertical fold over

(11) 1. V.Sync jumper V.Sync loss i.e.

2. Rotate Preset Pr403 Picture rolling vertically.

(12) 1. V.BLK jumper Retrace lines with picture

(13) 1. Remove J1 or J2 jumper Vertical Center position of picture improper

80

(14) 1. Interchange V1 and V2 Vertical scene reversed

Wires of Picture tube

(C). Horizontal Section: -

(15) 1. HFB jumper Horizontal phase shift

(16) 1. Rotate Preset Pr601 H.Sync loss i.e.

(17) 1. CCS jumper V.Sync , H.sync and loss of colour picture.

Picture rolling diagonally.

(18) 1. Rotate Pr602 Horizontal Centre position of picture not proper

(19) 1. Keep mute switch in Snow sound will be heard during no station

off position

(20) 1. Remove +12V jumper No Raster

(D). E.H.T. Section: -

(21) 1. H1 or H2 jumper Vertical Line

(22) 1. H. Drive jumper No raster, R728 burns.

(23) 1. Rotate Linearity Coil Less or more width

Magnet.

(24) 1. Remove Beam stab Excessive Contrast

Jumper J3

(25) 1. Interchange H1 and H2 Horizontal scene and letters reversed

Wires of Picture tube

(26) 1. Rotate Screen pot on White level and Brightness increases or decreases

EHT Xmer

(27) 1. Rotate Focus pot on Picture defocuses.

EHT Xmer

(28) 1. Remove H.BLk jumper Half picture black.

(E). Video Amplifier Section: -

(29) 1. +150 V jumper Retrace Lines

(30) 1. VDR jumper No Red Colour in the picture

2. R jumper

(31) 1. VDB jumper No Blue Colour in the picture

2. B jumper

(32) 1. VDG jumper No Green Colour in the Picture

2. G jumper

(33) 1. Rotate Pr25 Green colour increases or decreases in Black

level of B/W picture

(34) 1. Rotate Pr15 Red colour increases or decreases in Black


81

(35) 1. Rotate Pr35 Blue colour increases or decreases in Black


(36) 1. Rotate Pr21 Green colour increases or decreases in White


(37) 1. Rotate Pr11 Red colour increases or decreases in White


(38) 1. Rotate Pr31 Blue colour increases or decreases in White

Level of B/W picture

(39) 1. Remove J9 Red colored (tinted) picture with retrace Lines

(40) 1. Remove J10 Green Colored picture with retrace lines

(41) 1. Remove J8 Blue colored picture with retrace lines

(F). Colour Decoder Section: -

(42) 1. Rotate C875 B/W Picture O.K. but no Colour

(43) 1. Rotate Pr901. Colour decreases or increases

(44) 1. Rotate Pr802 Black level of picture changes

(45) 1. Jumper J4 Colour and B/W picture shifted i.e. blurred edges

(46) 1. Jumper J6 No colour

(47) 1. Jumper J7 Improper colour

(48) 1. SCP jumper No raster, only pickup when jumper touched

(49) 1. E.Bias jumper No raster, only pickup when jumper touched

(50) 1. Rotate L853 Colour sharpness changes

(51) 1. Rotate L860 Colour spots in B/W transmission

(52) 1. Rotate L880 Venetian blind line increase in picture

(53) 1. Keep Colour Switch Actual information about whether colour is present

in ON position or not displayed on screen

(G). Video I.F. Section: -

(54) 1. CVD jumper (J1) Raster O.K., Sound O.K., No Picture

(55) 1. Rotate Pr201 anticlockwise Snowy Picture/Weak picture

(56) 1. Rotate Video detector Coil Sound/Picture mismatch

(57) 1. Rotate Video detector Coil Color in picture vanishes

(58) 1. Rotate AFT Coil Range of AFT action reduces

(59) 1. Rotate AFT Coil Sound/Picture mismatch occurs

(60) 1. Keep AFT Switch AFT action vanishes

82

in OFF position

(61) 1. Rotate Pr201 fully Clockwise Black sync disturbed Picture due to overgain.

(62) 1. Rotate Sound trap coil L202 Sound bars occurs in weak transmission

(63) 1. Rotate input coil L201 Picture become snowy in transmission

(64) 1. IF jumper Weak or no picture

(H). Sound I.F. and Audio amplifier Section: -

(65) 1. SIF jumper Weak or No sound

(66) 1. Detune L302. Distorted Sound

(67) 1. Detune L302. Less Sound

(68) 1. Rotate Preset 100k Sound cannot be reduced by Volume control

in OPU/RR section

(69) 1. Remove jumper at Pin 3 Sound Distorted

of IC301 -CA1190

(70) 1. Remove jumper at Pin11 Sound Distorted

of IC301 -CA1190

(I). Tuner Section: -

(71) 1. +12V jumper to Tuner Only snow, No Picture, No Sound

(72) 1. Remove AFT jumper AFT action vanishes

(73) 1. Remove AGC jumper Picture becomes snowy

(74) 1. Remove LB jumper Band I channels not possible to

Tune

(75) 1. Remove HB jumper Band III channels not possible to tune

(76) 1. Remove UB jumper UHF channels not possible to tune

(77) 1. Remove TU jumper No channel possible to tune on any band

(J). Remote Receiver Section: -

(78) 1. Remove G-OSD jumper No green signal on OSD

(79) 1. Remove R-OSD jumper No Red signal on OSD

(80) 1. Remove B-OSD jumper No Blue signal on OSD

(81) 1. Remove Relay jumper No operation of S.M.P.S.

(82) 1. Remove CON jumper No operation by Contrast + or -

(83) 1. Remove BRT jumper No operation by Brightness + or -

(84) 1. Remove COL jumper No operation by Colour + or -

(85) 1. Remove VOL jumper No operation of Volume + or -

109

CHAPTER - 35

GLOSSARY OF THE TECHNICAL WORDS.

APERTURE MASK:

A metal plate with accurately formed holes, placed closely behind the phosphor -dot coated screen in a

colour T.V. picture tube. Its function is to ensure that each of the three electron beams strike only the desired

colour phosphor dot associated with the beam. This is also known as s hadow mask.

ACC:

Automatic Colour Control.

AFC:

Automatic Frequency Control - An arrangement for automatically controlling the frequency of an

oscillator against some reference. In television this term is used mainly with reference to the checking and

correcting the frequency of the line oscillator.

AFT:

Automatic Fine Tuning - An arrangement normally used in colour T.V. receivers to automatically check

and correct the frequency of the local oscillator in the tuner. This ensures that the video IF re mains at the

correct value and eliminates the need of frequent adjustment of the manual fine -tuning control.

APC:

Automatic Phase Control - This refers to the arrangement used in colour television receivers for checking

and correcting the phase of the regenerated colour sub-carrier.

ACTIVE LINES:

The television image lines actually visible on screen of picture tube. Number of lines per picture are 625.

Out of these approximately 585 are active, the remaining occur during the vertical retrace period, when the

viewing tube is blanked out.

ADJACENT CHANNEL:

The channel immediately above or below the reference channel.

ALIGNMENT:

Adjustment of tuning circuits so that they respond to the designed frequency or band of frequencies.

AQUADAG COATING:

It is the conductive graphite coating on inside glass wall of picture tube funnel or bell, that extends from

face plate or screen to about halfway into the narrow neck. This coating acts as final anode.

ASPECT RATIO:

Ratio of width to height of picture frame.

ATTENUATION:

Term used to denote a decrease of signal magnitude.

AUDIO:

Current or frequencies corresponding to sound waves.

AUTOMATIC FREQUENCY CONTROL:

The purpose of automatic frequency control (AFC) in a television receiver is to keep phas e and frequency

of receivers horizontal oscillator synchronized with phase and frequency of incoming sync pulses

AUTOMATIC GAIN CONTROL:

A circuit arrangement, which adjusts the gain of a receiver and keeps the output relatively constant, in

spite of variations in strength of input at aerial.

110

AUTOMATIC VOLUME CONTROL:

A circuit to maintain audio output level to a pre -set value.

BRIGHTNESS:

The sensation whereby, to the human eye, an area (or an object) appears to emit varying levels of light

from black to gray to brilliant white.

BALUN:

An impedance-matching device for antennas; used between transmission.

BANDWIDTH :

The difference, expressed in Hz between two frequencies that are the upper and the lower limits of a band of

frequencies.

BAR GENERATOR :

A generator for producing pulses equally separated in time that are synchronized so they produce a

stationary bar pattern on a television screen for test purpose.

BEAM :

The stream of electrons passing from the cathode to the fluorescent screen of a cathode ray tube.

BLACKER THAN BLACK REGION:

The portion of video signal above the black level. It contains the synchronizing pulses.

BLANKING:

The process of applying negative voltage to the control grid of cathode -ray tube to cut off the e lectron

beam during the retrace or fly back period.

BLOOMING:

Increase in picture size due to over -sweeping because of reduced high voltage to final anode of CRT.

BOOST SUPPLY:

A high voltage D.C. supply produced in horizontal output section. This booste d B + Voltage is commonly

used for horizontal output tube, vertical oscillator and first anode of picture tube.

BRIGHTNESS CONTROL :

A control in a television receiver that varies the average illumination of the image, on screen by varying

the bias on the cathode-ray tube.

CAMERA:

Download - Tv Lab Mannual

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