tv lab mannual
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R.K.D.F INSTITUTE OF SCIENCE & TECHNOLOGY
DEPARTMENT OF ELECTRONICS & COMM. ENGG.
COLOUR T.V. TRAINER
Specifications of Colour T.V.
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. 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
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.
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.
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
3. To separate the combined luminance (Y) and chroma signals from the video IF Signals and to amplify
4. To separate the luminance (Y) and chroma i.e. U & V (R -Y and B-Y) Signals from the combined video
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.
BLOCK DIAGRAM OF THE COLOUR T.V.
(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 n