After playing fine for a few days, the game powers up with only general illumination; the MPU LED gives no flashes at all. New connectors on the rectifier board didn't help.

Only GI lights and MPU LED never flashes: loose wiring at J3 on the solenoid driver board

Cause: Loose wiring in the J3 connector on the solenoid driver board, so power from the driver board's regulator was not reaching the MPU.

Checks

• Measure the rectifier and driver board test points, then 5 V and 12 V at the MPU.
• Check the 12 V feed from the rectifier to the driver board's regulator.
• Repin both halves of the driver board connectors, especially J3.

Fix

• Repair the loose wires and pins in the J3 connector on the solenoid driver board (replace the housing and pins if worn).

The driver board carries the high-voltage display supply (over 200 V); take care when measuring.

Systems

• Bally MPU AS-2518-35

Games

• KISS

Related tips

• Only the GI lights and the MPU won't boot: bad connection at J3
• MPU won't boot and driver board test points read low: replace the solenoid driver board
• MPU stops before the 7th flash until sound board power is unplugged: replace CR3
• Bally MPU loops through its 7 flashes and resets: check R134 and the interrupt traces
• Four switches on one return line dead with good wiring: failed 6821 PIA on the MPU
• Background sound works in test but not in games: check DIPs 29-30, then reseat connectors
• Display digits flicker then vanish after the game warms up: poor board connector contact
• Only three players allowed on an aftermarket MPU: reseat J1, clear memory, reset DIPs

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