At switch -on the set behaves quite normally, the sound signal starts to build up and then as the line timebase comes into operation the sound
vanishes and an only partially controllable raster
appears. As this happens, the video anode voltage drops by some 30V. After this, the picture and
sound appear very briefly from time to time. -L.
Newman (Oxford). This symptom could be caused by instability in
the vision stages. The oscillatory signal so produced would be rectified by the vision detector
and overdrive the video amplifier, causing its
overheating. The vision and possibly the sound
would be affected. Check the i.f. valves, preferably by substitution and, if necessary, the small i.f.
decoupling and bypass capacitors.