After repairing a battery-damaged MPU, the game boots reliably but the feature (controlled) lamps flash on for a moment at attract mode and then stay off; displays, coils and sounds work in the burn-in test.

Feature lamps dead after an MPU repair, GI fine: reseat MPU plug J3

Cause: A poor connection at MPU connector J3; unplugging it and plugging it back in restored the lamps.

Checks

• Check the work done on the board, including any new chip sockets.
• Following the usual troubleshooting guide, boot with J3 unplugged, then plug it back in with the power off and recheck.

Fix

• Reseat J3; repin the MPU's 0.100-inch connectors for a lasting fix.

Systems

• Stern MPU-100

Games

• Nine Ball

Related tips

• Repair battery corrosion before chasing MPU flash codes
• Seven flashes but no attract mode
• All score displays blank with the MPU fully booting
• Repairing battery corrosion on the MPU
• Sometimes three flashes, sometimes seven, with flickering scores
• MPU on the bench always stops one flash short
• Intermittent or dead MPU from old closed-frame sockets
• MPU boots only when U9 pins 39 and 40 are shorted

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