[Coco] Buyer beware
msmcdoug at iinet.net.au
Mon Feb 23 17:57:25 EST 2009
> Screenshot at http://www.sq1bbs.com/3002coco.jpg
Is this image consistent each time, or somewhat random?
Years ago I got an old Juno First arcade PCB that had partly corrupt
sprites. I suspected RAM but the trouble is the PCB had a sea of 4116's -
all NON-socketed - and I had no schematics. So I had an idea...
I modified the MAME driver to simulate a single _faulty_ RAM chip in the
sprite circuit. Then I ran the emulator, and checked what it showed against
what I was seeing on my arcade cabinet. After switching bit positions a few
times, I got exactly the same corruption I was seeing on my cab!
Back to the PCB, there was (IIRC) enough indication of which bank of memory
was for sprites. I located what appeared to be the chip for that bit
position, unsoldered it and replaced it with a socket and new RAM chip.
Fired it up and - lo and behold - no more corruption!!!
Anyway, the point of this ramble is that perhaps doing the same in the Coco
MESS driver might be an option - at least it might _prove_ it's a RAM
problem if you can reproduce the same garbled graphics???
I'd give it a go myself but I'm about to head off to work... maybe later if
you're still having problems???
BTW when you checked for loose chips, did you press down _quite firmly_ on
each socketed chip? "Loose" doesn't mean "I can wiggle it when I touch it"
in this case.
| Mark McDougall | "Electrical Engineers do it
| <http://members.iinet.net.au/~msmcdoug> | with less resistance!"
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