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 Post subject: [MSC-4000] Video output problem
PostPosted: 10 May 2023, 12:49 
Genuinely interested
Genuinely interested
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My Sony MSC-4000 has developed what I think is the exact problem described in I isolated the problem to the top right board (which seems to do most of the processing -- the other boards are the power supply to the left and the lower board is quite sparsely populated and seems to contain the microcontroller that reads input buttons and adds the on screen display among other things. I swapped boards between this and a working decoder, and the result is consistent.

I've looked at solder joints and re-flowed quite a few that looked a bit "dry". The caps look fine, but of course they're old so might not be. I've measured most of them with an ESR meter and taken off a few that couldn't be measured in curcuit -- they've all measured ok, but of course I replaced them anyway.

I took a few pictures:

File comment: Light dots
20230428_002009.jpg.small.jpg [ 402.1 KiB | Viewed 1033 times ]

File comment: Greyscale
20230428_003217.jpg.small.jpg [ 277.44 KiB | Viewed 1033 times ]

Maybe the greyscale test pattern has some hint: it seems there is excessive noise in the dark grey area -- the other areas seem fine. Could this be a bad D/A converter, or hopefully, some electronics surrounding it? Any other ideas?

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