The GI lamps are out on all or part of the game, which looks dark.

General illumination dead or dim

Cause: Burnt .156 inch GI connectors are the usual cause: the pins overheat, solder joints crack and the resistance builds until a pin falls out or burns. Cracked solder on the GI relay and cracked PPB fuse clips are next.

Checks

• Follow the GI path and inspect every plug: transformer (four yellow wires), the 4-pin plug about ten inches from the transformer, power supply input, the GI relay, power supply output, PPB input, the PPB fuse and clips, and the PPB output.
• Test the GI fuses on the PPB out of their clips.

Fix

• Replace burnt housings, pins and the board header pins.
• Reflow the GI relay and replace bad fuse clips.

Unplug the game before working on the transformer, line wiring or power supply board.

Systems

• Data East CPU Version 1/2
• Data East CPU Version 3
• Data East/Sega CPU Version 3b

Related tips

• Burnt GI traces on power supplies of Time Machine and earlier
• GI will not switch on or off: power supply relay RY1
• A group of general illumination lamps is out
• Bulb spares: #44 for CPU lamps, #47 for general illumination
• Random coils firing and dead flashers on Tales from the Crypt
• Won't boot, only some lamps on: bad capacitor joints on the power supply board
• Tales from the Crypt: random coils and dead flashers from a wrong K-1 relay
• Several bank-switched coils or flashers dead, or firing the wrong device

Source: Repairing DataEast 1987 (Laser War) to Sega 1995 (Batman Forever), Part One, Clay Harrell (pinrepair.com)