After a few good games the background sound drops out and the game locks up: coils stop working and the score displays go dark while the GI and backbox lamps stay lit. Wiggling wiring or a hard hit on a target can bring it back or lock it up again.

Game locks up mid-game, sounds stop and displays go out: MPU connectors and loose ROMs

Cause: Poor connections at the MPU board connectors and ROM chips that had worked loose in their sockets.

Checks

• Check the board supply voltages at the power supply test points.
• With the power off, reseat the MPU connectors and the interconnect between the MPU and driver board, and look for cracked solder joints on the header pins.
• Press each socketed ROM and chip firmly back into its socket.

Fix

• Repair or repin the faulty MPU connectors, reflow cracked header joints, and reseat the ROMs.

Systems

• Williams System 6 / 6A

Games

• Time Warp

Related tips

• Background music stops at random until the next ball: game ROM bug

Source: Pinball Repair help group!! (Facebook group)