The game powers up with general illumination only: no displays, and the MPU LED gives no flashes. A previous owner had hacked the wiring at J3 and TP4.

Only the GI lights and the MPU won't boot: bad connection at J3

Cause: A poor connection at J3 on the solenoid driver / voltage regulator board, the plug that brings in the unregulated supply and sends 5 V back out to the MPU. Wiggling J3 made the game boot.

Checks

• Check all the rectifier board test points first.
• With power on, gently wiggle J3 on the solenoid driver board and watch the MPU LED.
• With the board out, inspect the back of the J3 header for cracked solder joints and lifted traces.

Fix

• Undo any hacked wiring, resolder every J3 header pin, and repin or replace the J3 plug.
• Check J4 on the same board too, another plug that often gives trouble.

The rectifier and solenoid supplies are high enough to hurt (solenoid power is over 40 V DC and display power far higher); work with the game off and unplugged.

Systems

• Bally MPU AS-2518-35

Games

• Silverball Mania

Related tips

• Only GI lights and MPU LED never flashes: loose wiring at J3 on the solenoid driver board
• Pre-Xenon transformer to rectifier board wiring
• Early Bally SS rectifier board: worn ground mounting pad and cracked header pins
• Pre-Xenon rectifier board outputs by connector
• AS2518-18/-49 connector functions
• Replace browned rectifier header pins and housing pins together
• Burnt rectifier J3 pins 8 and 17
• Rectifier board J3 pin functions (pre-Xenon backbox transformer)

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