8296D repair (continued)

From: Nicolas Welte (welte_at_chemie.uni-konstanz.de)
Date: 2002-02-05 14:13:30

Some may remember that I had a 8296D board that lacked some parts. That one
works fine, after I used a 74F374 as replacement for the 74S374. But I still
have the original board of that machine, and I'd like to repair it.
Especially after I saw another board with exactly the same symptoms: No
startup sound, no IRQ present, but the CPU obviously accesses the ROM in a
very regular manner (looks like an endless loop or something), checked with
an oscilloscope connected to the ROM's CS line. All the socketed chips (CPU,
6545, ROMs, one PLA) are good. I don't have much of an idea what to look for
now, and I'd be happy to get some hints.

BTW, the other board is from Paul Foerster's 8296D, which he got from Ruud,
if I got the story right. Paul visited me this weekend and brought his dead
original PET 2001 and this 8296D with him. We managed to get the 2001
working, but didn't have time to look closely at the 8296D. The 2001 had a
missing VSync signal, and since this seems to be the only IRQ source in this
machine, it didn't start up at all. I wonder if all PETs/CBMs work this way?


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