On Dienstag, 18. April 2017 13:34:58 CEST you wrote: > >> Hi all, > >> I have found a real tricky fault on my C64C. I'll try to describe the > >> symptoms, in case anyone is curious enough to help in troubleshooting > >> it. I am not a newbie in repairing C64s, but this one made me just > >> wondering without even giving me a clue on where to start probing for > >> possible faults (if I had a logic analyzer I would know what to do, > >> but I haven't got one). > > > > Logic analysers may not help in some edge cases like this one. > > > > The nouns you mention (VSP, sprites, ..) seem to be pointing towards the > > VIC. I'd check its voltages, frequencies and eventually swap it. > no VSP errors showed from a tool that's supposed to check for their > existence on a C64, so yes, the VSP was mentioned and likely excluded. > The crashes are very repeatable infacts, all happens every time at the > same point of some programs. Most (all I could try) programs show no > random or repeatable errors. > I don't have any other MOS 8565 VIC-II chip to try swapping it. I only > have old 6569s From your description of a sprite "almost?" touching the bottom of the screen... And the fact that it's always at the same position, so that it's really repeatable points to a logic error, not a timing error. Maybe it's a stuck sprite collision bit, that once set is not reset and keeps the interrupt low? You could write a simple test program for that. Regards, André Message was sent through the cbm-hackers mailing listReceived on 2017-04-18 12:02:21
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