Westinghouse H886K21

[FrankieKat]

Originally Posted by Electronic M

Is the 100K resistor in series with the CRT HV lead still original? If so try replacing it. I mentioned earlier that resistors in the HV can develop internal arcing, the arcing acts like a spark gap transmitter and feeds back through the RF chain as video and audio interference.

No, that one is original, though I tested it and value was good. I'll replace it next time I pull out the HV box (it's not a lot of fun to do on this).

Originally Posted by Electronic M

Was the 3RD IF tube installed when you injected after it? If so large RF noise spikes could still be getting through the IF and mix with the injected signal resulting in the noise remaining present. If you pulled the 3RD IF for the signal injection then it suggests a noisy component, B+ line, or connection in the stages between the injection point and the element of the CRT being driven with video.

It was removed, and I also removed the 1st IF and injected signal right after it. I will repeat the experiment again tonight and make detailed notes about what happens.

Originally Posted by Electronic M

Do you have a working o-scope? If so it may be good to ground out the signal going to the detector (a large cap ~.1-10uF from it to ground should do the trick) and if the noise persists search for it in the stages between there and the CRT. Once you find it trace it in in the signal chain to the strongest point, then look for it on any power supply lines in the area to see if it is stronger in those lines.

I do, and I'll give that a try. It's tricky because the noise either goes away or becomes imperceptible with low or no signal. With the antenna leads disconnected or IF tube pulled the screen is solid white/blank.

Do you think this is related to the AGC or do I have two unrelated problems?

Thanks for the suggestions -- will get to work on those next and let you know.

FK