K7400 / WGM2574 partial vertical collapse

wolf340

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I have a K7400 showing a partial vertical collapse issue. Bright line in the middle and about one third of the video is showing fine below the line. Picture attached.

I have done a full re-cap on the P793 board and it made no difference. Measured the pots on the remote board, especially the 200K height pot. It seemed OK through the 200K range and shows height adjustments in the visible part of the video.

Also tried replacing D302 and Q601 with no difference. I measured R402, R303, R627, R618 in circuit and they seem to be OK. B+ voltage on TP202 seems OK (117.2V). I also do get 24.75V on pin 9 of U601.

I am running out of ideas. What would be my next best bet to track this one down? Does the screenshot look like it could be a defective U601?

Thanks
 

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if you put a quality cap kit in and don't have any bad caps then i would say recheck all work and u601 could be bad to start with because everything else that would be obvious its sounds like you have done a pretty thorough start in checking things. the other thing is before the cap kit what was the problem???
 
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Exact same problem before the cap-kit. I did the cap-kit in an attempt to fix this and also because it has not had one for almost 15 years.
 
Replacing U601 did the trick. It was complicated by the fact that the first replacement TDA1771 I received was bad. Now with a good one installed the board works fine again.
 
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