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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: 1, Interesting) by Anonymous Coward on Tuesday April 15, @03:12AM
Oh, all those chips dying, I felt a great disturbance in the Force, as if millions of voices suddenly cried out in terror and were suddenly silenced.
(ha ha!)
Still hurts that a very long time ago I killed 5 or so antique vacuum tubes in an antique radio. Very accidentally swapped the 1.5V heater supply with 75V plate supply (or whatever the voltages were).
Once I had to repair a small TTL logic board. 20 or so chips. 5V was being drawn down. Simple linear regulator which had overload / short-circuit protection. IIRC chips were soldered in.
So, I connected a high-current 5V supply and very quickly the dead chip got very hot, probably blew out some smoke. Changed it and the rest worked.