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Originally Posted by vol.2
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Edit: I think it's worth mentioning that I also see the bars if I directly insert an RGB signal into the RGB mux chip on the video processing board. I did this as an experiment to see if I could inject RGB via the mux chip in place of the OSD signal and blank the screen to show a higher quality signal (I succeeded), but I did notice that I was getting the bars in the image this way too. This would leave me to believe that it's nothing about the composite input board or demodulation circuit that is effecting things at least. This set is a Toshiba, so it uses one of their optical isolator chips to get the composite video in without the need for an AC transformer to isolate the set (the optical IC has a separate ground).
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If it's not coming in on the previous stages, and all the caps are good, where else could it be but on grounds is what's puzzling me.
I think I would make a quick test of bridging a cap across C446, and triple checking it's the right value, and maybe bridging it to a different ground point on the circuit.