I have a pair of dead Galaga pcb sets (real midway, not clones) from which I trying to revive one. Not having a working set for reference, I don't have a good comparison point, but am making some progress. After replacing the 74128 on one of the PCB boards, I got it up and running. Logic probe testing indicates that its accessing memory, reading the dip switches, etc. However, I could not get any video. After pairing up with the video board from the opposite set, I finally got the images shown below.
It looks like the unit is probably trying to do its self-test, but the screen is mostly garbage. The most telling characteristic is the "banding" of the character generator. You can see it in both attached pictures. In the first, the non-character area has the starfield generator (which appears to be working fine). In the second, the non-character area is pure white and the characters generator area contains more random looking symbols than the zeroes in the first image.
I have already cleaned and reseated all the socketed chips and swapped the 07XX and 04XX customs between the two boards (which didn't make a difference).
Appreciate any suggestions on where to look next!
It looks like the unit is probably trying to do its self-test, but the screen is mostly garbage. The most telling characteristic is the "banding" of the character generator. You can see it in both attached pictures. In the first, the non-character area has the starfield generator (which appears to be working fine). In the second, the non-character area is pure white and the characters generator area contains more random looking symbols than the zeroes in the first image.
I have already cleaned and reseated all the socketed chips and swapped the 07XX and 04XX customs between the two boards (which didn't make a difference).
Appreciate any suggestions on where to look next!
