Rectifier TP3 has +12 V but MPU TP2 does not.

12 V at the rectifier board but not at the MPU

Cause: Usually one connection: the orange 12 V wire at rectifier connector J3 pin 8 is often burnt.

Checks

• Inspect and test continuity of the orange wire at rectifier J3 pin 8.
• The 12 V runs into the solenoid driver board on J3 pin 12 and back out on J3 pin 11 to the MPU; check both pins.

Fix

• Re-pin rectifier J3 pin 8 with a new crimp pin (and the matching header pin if it is discoloured).

Systems

• Bally MPU AS-2518-17
• Bally MPU AS-2518-35
• Stern MPU-100
• Stern MPU-200

Related tips

• +12 V at the rectifier board but not at MPU TP2
• No +12 V at the MPU: check the rectifier board
• Rectifier board J1 (to playfield) pins
• Rectifier board J2 (to cabinet) pins
• Rectifier board J3 (to backbox boards) pins
• Game starts but won't fire any solenoid except flippers: repin J4
• MPU gives 3 flashes after reassembly: two 15-pin plugs swapped
• Burnt pins at solenoid driver J3

Source: Repairing Bally Electronic Pinball Games from 1977 to 1985, Part Two, Clay Harrell (pinrepair.com)