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A tricky Commodore PET repair: tracking down 6 1/2 bad chips

> I typed in a simple program to generate an animated graphical pattern, a program I remembered from when I was about 13 [...]

I'm astounded that anyone would be able to remember such a complicated program after several decades. About all I remember from those days is:

  10 PRINT "HELLO";
  20 GOTO 10;

5 days agoby kmoser

How could the computer be operating well for the most part, yet also completely wrong?

Anyone who has done any overclocking knows about that. When signals or timing are marginal, intermittentness appears. In the PC world, programs like Memtest86+ and Linpack are great at stress-testing to find marginality, but I'm not sure if such software was as common in the 8-bit era.

5 days agoby userbinator

I don’t personally have the time or inclination to do any retrocomputing, but I love seeing the repairs that people do for them. It’s interesting in a way I wouldn’t have expected. Thank you for sharing.

5 days agoby cshokie

Amazing that they were able to figure this out. I have a PET that also sometimes boots up into a garbled screen similar to the one pictured in the article. I am usually able to get past it with a few hard resets. I don’t have access to (or much knowledge of) logic analysers, but this almost makes it look doable to figure out the problem.

5 days agoby micheljansen

Author here if anyone has questions.

5 days agoby kens

That PET is in amazingly good physical shape. I think the keyboard on my 8K PET back in 1978 looked that bright for at most a year or so, before the plastic overlays started fraying.

5 days agoby philiplu

That keyboard doesn't look like fun to type on. The one on the VIC-20 and C-64 were pretty okay!

5 days agoby dep_b

This is wonderful to read. I'm about to embark on getting my Sharp MZ-80K into good shape for the next 40 years. It still works fine but I bet there are a bunch of capacitors just waiting to die, and solder joints that are waiting for the perfect day to fail.

5 days agoby jgrahamc

I have one in pristine condition for sale (in Europe, willing to ship worldwide).

5 days agoby morphle