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http://www.righto.com/2025/04/commodore-pet-repair.html
In 1977, Commodore released the PET computer, a quirky home computer that combined the processor, a tiny keyboard, a cassette drive for storage, and a trapezoidal screen in a metal unit. The Commodore PET, the Apple II, and Radio Shack's TRS-80 started the home computer market with ready-to-run computers, systems that were called in retrospect the 1977 Trinity. I did much of my early programming on the PET, so when someone offered me a non-working PET a few years ago, I took it for nostalgic reasons.
You'd think that a home computer would be easy to repair, but it turned out to be a challenge. The chips in early PETs are notorious for failures and, sure enough, we found multiple bad chips. Moreover, these RAM and ROM chips were special designs that are mostly unobtainable now. In this post, I'll summarize how we repaired the system, in case it helps anyone else.
(Score: 2) by ChrisMaple on Tuesday April 15, @02:32PM
There's a good chance that reprogramming (without erasing) at the below-spec voltage would shift enough charge to correct the bad bits. The risk is that they'd still be marginal; that they'd be erratic and the first to fail again as time passed.