Double-check bench leads: a +12 V to +5 V short kills the MPU chips

Shorting +12 V onto the +5 V rail will likely destroy every chip on the MPU. TP2 (+12 V) and TP3 sit right next to each other and are easy to bridge with a clip, so check every lead before switching the bench supply on.

A misplaced +12 V clip can destroy the MPU chips.

Systems

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

Related tips

• Using a PC power supply as an MPU bench supply: which wires
• Where to clip a bench supply onto the MPU
• Reseat the MPU chips before anything else
• Strip the MPU to three chips to get the first flicker
• Power and ground pins of the main MPU chips
• Testing an MPU in the game with only J4 connected
• MPU board test points
• Intermittent MPU faults from old closed-frame chip sockets

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