If you have access to an eeprom programmer and some replacement roms, you can program up the mask roms and piggyback them one by one. Alternatively you will need to use a logic probe to go around the pins on the roms to see if there are any legs that are not changing or are floating. The background in the left image should be blue and its white in your's.
I have seen similar faults caused by bad traces due to corrosion, sram, mask roms, 74LS393 IC's, custom IC's and anything else you can think of. Unfortunately these boards can be difficult to repair if your not experienced.
