As for RAM versus ROM problems: it might be that the firmware is copied from ROM to RAM before it is started in earnest.
I have worked on a design like that in the dim past. Reason for doing this: 32 bit wide RAM ran a lot faster than 16 bit wide 27512 EPROMs. Using a 68020 at the time by the way.
So.. bad RAM could also haunt you for program code...
