Neo Geo Arcade board problems

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