Customer brought in a Baywatch that had been sitting in storage for 10 years. It is a reimport game and the customer was afraid that the transformer had been wired wrong. Turning the game on resulted in no lamps and a scrambled display. This game uses the very large (and very expensive) 192×64 DMD display that was only used in 4 games. Swapping in a known good MPU did not resolve the display issue. Swapping in updated Eproms did not fix the issue. Swapping in known good cables did not fix the issue and I do not have another large display game in house but have a friend with this title so it was time to bring the display and display driver board over there to test them.
Tested the driver and it worked fine in the other game, Tested the display and the other game and the symptoms persisted so unfortunately it is a problem with the large display. The large display is the Chery Brand display (3 different companies made this display)
Put the large display back into the original game and time to investigate what the issue may be. These large boards have their own on-board power supplies to change 12V into the higher required 70V and -110 volts. Checking these voltages showed that both were too high. Looking over the board I could see that the Capacitor at C32 ( 33 uf 160V) was bulging on the back. Replaced this capacitor with a new one and voila, the display was unscrambled.
Now on to fix the switch issues….