On Sun, Nov 26, 2017 at 3:02 PM, Adrian Graham via cctalk <cctalk@classiccmp.org> wrote:
>> What happens if C101 is removed? Also try running it with TR101 >> removed (or at least the emitter lead of that transistor disconnected). > > Nothing happens, in that the picture is the same as it is with both those > components fitted. That suggests the problem is not in the contrast control or the clamp transistor TR101. I would suspect TR102, TR103 and associated components. I don't have the schematic with me at the moment, but as I remember it you can look at the connection between TR102 (common emitter stage) and TR103 (common base stage on top of it) on one of the connections to the CRT base PCB. And of course the output of the video amplifier on the CRT cathode pin. It would be worth looking at the signals on those points with a 'scope, see what amplitude of video signal (not the 'standing' DC level). -tony
