I would be testing each display individually with others unplugged
I will check schematics tomorrow as I can't remember what drives the 1 segment. On system 1 games the use two separate chips, ls21 from memory, to drive the 1 segments, can't remember if system 80 is the same, so I wil check tomorrow. Also I have seen crook 5101 ram cause display issues.
I won't be surprised if it a bad 5101 - but it is easy to rule out. Run the full tests, and you would see the 5101 Error. Also check the ROM test. Unfortunately I don't have a sys80a schematic to follow, but it sounds like a board problem rather than display. Would be great if you could isolate the CPU / Display if you have another handy.
