I have a South Park with no lamp matrix lamps lighting.

18vdc fuse is good, the 18vdc led is lit but no lamps.

Machine boots, runs, flashers and coils are all working. Previous owner installed ColorDMD, and that is working. The DMD driver board is reused but the dmd display board was removed and the plug from the display power supply board was left unplugged.

They had put some LEDs in the controlled lamps but not sure that would be a problem. But not a single lamp is working, the bridge rectifier is cold to the touch, and the 18vdc LED is lit. I would assume we have 18vdc to lamp column drivers and the row returns would be good, as is U6, because the game is running and U6 tickles the watchdog. I think if all lamps are out, my guess is that U18 is bad if the game runs but there are no lamps at all lighting, U18 is the high side column driver, and if it failed, that would keep all lamps off, but the game would still run.

Am I anywhere near right? Is there anything elese that would let the game run, but cause the controlled lamp matrix to go completely dark?

Is a failed U18 a common cause for all lamps out?

Had typo on my chip designator... that is U18 not U16...