Monochrome TV Receiver Circuits and Stages
What this domain tests
Monochrome TV Receiver Circuits and Stages tests the signal path and stage-by-stage faults: tuner, IF, video detector, video amplifier, sync separator, deflection, EHT, AGC, and sound takeoff.
Core rules
- Antenna → tuner (RF amp, mixer, local oscillator) → IF amplifier (picture IF about 38.9 MHz in PAL B/G; sound intercarrier about 33.4 MHz) → video detector → video amp → CRT cathode.
- Sound takeoff extracts the intercarrier; sound IF is about 5.5 MHz in PAL B/G or 4.5 MHz in NTSC M, then FM detector and audio amp.
- Sync separator slices composite video; vertical and horizontal oscillators drive deflection coils.
- The horizontal output stage also produces EHT via the flyback transformer; a fault can remove raster and damage the output transistor.
- AGC controls tuner and IF gain; failure causes overload, tearing, or weak contrast.
Worked example
A monochrome TV has sound but no raster. Sound proves the tuner, IF, detector, and sound chain are partly alive. Check the CRT heater, EHT, horizontal output and flyback, and video amp supply. If EHT is absent, trace the horizontal oscillator and output. If EHT is present but the screen is dark, check CRT cathode voltage and the video amp. This split-half reasoning avoids replacing the tuner blindly.
Traps
Assuming no picture means a tuner fault is wrong. Ignoring EHT hazard can be fatal. Confusing the sound carrier frequency with the IF frequency leads to misalignment. Misadjusting AGC for a deflection fault makes diagnosis harder. Never check a CRT without discharging it first.