Back to the VT-71H

[Chris K]

Originally Posted by Yamamaya42

Looking at things closer, V6 has to be working for there to be sound, as the sound pickup is through C35, but perhaps problems with coils L32/L33 or C72, it should be easy enough to trace with a scope, cause you KNOW, it has to be getting as far as the video amp for sound, just need to see where it may be getting lost from pin 5 to CRT point C.

Back to this PIA TV inspired by Bob and his recent "Green CRT" video. I noticed the Sams and the Motorola service differ as to the direction of the 1N34 diode in the video detector. The service data has my chassis, VT-71H in it and the diode direction is the opposite configuration from how I installed it. I switched it around and it made no difference. I tried a different JP4 CRT to see if maybe there is a cathode issue with what I've been using and the "image", a full screen and bright raster with no video information getting to it, is the same. The sound coming off pin 6 of the video amp 6AU6 is clear and buzz free with plenty of volume. There's a new 0.047 uf cap replacement for the 0.05uf C-72. I've checked the 2 coils between the video signal off the plate and the CRT and their continuity and they are fine. Just for grins, I replaced them one at a time with the same coils off a parts chassis that tested fine with no change. Scope is down right now so I can't check signals but if I have audio getting through the detector, everything before it should be fine as far as the video signal correct? The only thing I have not confirmed are working are the 8 and 15 pf caps in the detector but they're the type that are supposed to never go bad. I am at a complete loss with this missing video signal. It's a real mystery. When I get my new, USB oscilloscope, I'll be able to do more accurate tests but until then, I'm totally stumped.