The game boots and starts, but won't kick a ball out or fire any playfield solenoid; only the flippers work. Coil voltage is present, every coil fires when its driver transistor is grounded, and a new MPU and new driver board behave the same.

Game starts but won't fire any solenoid except flippers: repin J4

Cause: Bad contacts in the J4 connection between the MPU and the solenoid driver board, which carries the solenoid select data.

Checks

• Check the solenoid fuse under the playfield.
• On replacement driver boards that split the 5 V supply, check both 5 V test points.

Fix

• Repin both ends of the MPU J4 to driver board J4 connection.

Systems

• Stern MPU-100

Games

• Nugent

Related tips

• 12 V at the rectifier board but not at the MPU
• Three flashes and 8s or 9s in the hundreds digit
• Rectifier board J3 (to backbox boards) pins
• MPU boots only some of the time
• MPU boots only when U9 pins 39 and 40 are shorted
• MPU locks with LED on because of C23 or Q20 on the solenoid driver board
• MPU board test point voltages
• How the MPU sees the 43 V solenoid supply

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