This is an old post, preserved for reference.
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Commodore PET's never fail to find new and interesting ways to fail. This is a new one on me. It started as a normal repair, black screen, no beep, usual 8032 faults, but took a lot longer than usual.
So far, so good, looks OK in general. One 4116 has been removed, and some tracks damaged and repaired on the back. I checked those out, no problems with that, all continuity fine.
previous repair, I was getting results that showed that 5 of the 8 bits were faulty. I was hoping it would be better than that. It could be addressing issues causing that, or it could indeed mean that 5 RAM chips were faulty. To test this, I removed one chip and tested it on my Spectrum DRAM tester.
The board is now back with it's owner. Here is his video showing the board being reinstalled in the case.