I have about four Neo Geo six slot arcade game boards with Video RAM
errors. It is not the actual video RAM, that much I have determined.
If your not familiar with this board it has a lot of large surface
mount chips with upwards over over a hundred pins each. It uses a
Motorola 68000 chip. Can someone give me some clues on how to track
this problem down? With this kind of error am I going to find an
address or data line that is stuck high or low? Or could it be another
pin. Nothing on the M68000 seems wrong, The chip checks out fine on a
tester. I have replaced the video RAMS and this M68000 so it must be
in another chip or in a trace. If I probe each and every pin of all of
the components would I for sure find the error or can this type of
error not show up as a hardware difference? Can this be a software
error? Lets say I find the pin that is not working, What would that
pin look like on a scope? Just a high 5 volt or low ground, or could
it be at a logic high or low, that it is just not transitioning from
one state to the next as it supposed to? Could it be more then one
pin? There is no documentation for this board at all. I am not sure
where to began and what to do next.
Thanks very much
Russ