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). Symptoms: 1) Lunatico demo from LFT freezes if started from the "note and vsp tool" (pressing F8 from the note loads some more bits from disk, then freezes). No VSP errors ever show while running the VSP tool. 2) Lunatico demo started with a LOAD"*",8:RUN works every time and never freezes or malfunction. 3) Concert demo (from Performers) freezes after the RUN command without even trying to load anything else from disk. 4) IC BURN-IN test program freezes always at the same point: when the rombic sprites go around the screen, it freezes when the first sprite almost touches the black bar at the end of the lower side of the screen. Hitting reset button makes the test re-start and it never shows any error on anything, but it freezes at exactly the same point every time. 5) No game that I could find on my vintage floppies collection ever showed any problem, I could play for hours everytime. It could be RAM or a slightly bad CPU (or what else?), but I hate desoldering things randomly. No RAM test that I could write or run ever showed any bad location. I was tempted to use an emulator with built-in cpu single-step option to try to pinpoint the freezing conditions, but as a matter of fact, I've never ran any C64 emulator so far (and time is always less than half of what I'd need to have). Anyone can come up with a reasonable hint? Thanks Frank IZ8DWF Message was sent through the cbm-hackers mailing listReceived on 2017-04-18 12:00:02
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