been trying to track down this problem for months (i am strictly an amateur). displays would flicker and eventually died altogether. i replaced the filter caps and C6 on the power supply. repinned the connectors and added additional grounds. no longer blowing the 69v fuse. cleaned up an accidental solder bridge, replaced a couple of blown diodes (CR3/CR4) and the four diodes that make up the bridge rectifier on the power supply (CR6-9). now instead of dead displays i get this:
checking the displays in the test menu shows no improvement. something is "working" because they change while scoring, but nothing usable. plugging/unplugging the individual displays didn't improve anything. all connectors are good and clean and snug.
noticed Z16 and Z17 (the 7448 decoders) on the MPU were screaming hot, made me wonder, though the game and sound proms were also hot and they still seemed to be functioning fine....
just found this regarding someone else's issue, but seems like it could also apply here:
"Since you said the problems show up same on players 1 and 2 and same on
players 3 and 4 - you need to look at digit strobes, not segment drivers.
Digit strobes are driven by Z18-Z21."
Z18-21 are 7408's
any feedback much appreciated!