Ram Error

This is maybe not a basic question but I guess it is all relative. I am working on a arcade game board that is operated by a M68000. (Neo Geo 4 slot). It comes up with a "Work Ram Error" I am pretty sure the ram is ok. I have compared it many times with a few Huntron style testers. There are about 6 SMD RAM chips. It shows an address and then what was written AAAA and what was read AAEA. Can someone provide me with some tips on how to track down the fault? The 68000 is tied to three custom 100+ pin smd chips and it is real hard to follow the traces to be sure because the board is not translucent and many of the traces go under chips. But what is the process generally used to wire up RAM and what could cause this read error? Are RAM chips generally wired directly to the M68000? Or do they have to go through some type of controller? Can a read error like this be caused by an open or short in the trace or is this something that is only caused by faulty logic in the RAM or faulty logic in another chip. It seems there are no short cuts but there is also no documents on this board. No schematics, no pinouts on the custom chips and no theory of operation. I am sure someone understands this more then I do. Thanks again Russ