First checks for any missing voltage

A missing supply is usually a blown fuse, a burnt header pin or a bad connector before it is a failed part, so check fuses and connectors first. Unplugging rectifier board J3 isolates the supply from the game and changes the TP2 and TP4 readings slightly.

Systems

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

Related tips

• A missing test point voltage: what to check first
• Rectifier board test point voltages
• Transformer secondary voltages and what they feed
• Safe first power-up of an unknown game
• MPU LED lit solid: check +5 V first

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