Don't even get me going on hacky solder jobs... Just got in 5 Williams dot matrix driverboards for pinballs for repair... someone already tried to 'fix' these... you should know these boards get pretty toasty in the powersupply section, and when you combine that with an amateur with a crappy -and- huge soldering iron... let's just say there are just a few traces less on these boards then I'd like...
Anyways, that looks like the ram adressing is messed up for the object roms. First thing I'd try is with the board hooked up and turned on, pull your fingers along the underside of the board on the pins of the ram chips and watch for any static/change. If you see any change, you've found your culprit. Also, if there are any Fujitsu chips on the board, those are always suspect...