New replacement MPU boards exist

Badly corroded MPUs are often not worth a paid repair, but a hobbyist can usually fix them. New replacement MPU boards are also made, some DIP-switch selectable for any Bally or Stern game and with improved diagnostics.

Systems

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

Related tips

• Fit the replacement MPU LED the right way round
• Testing an MPU in the game with only J4 connected
• MPU board test points
• MPU board test point voltages
• Why the MPU has ROM jumpers
• Telling a -133 MPU from a -35 or -17
• Converting a -133 MPU to a -35
• Setting up an MPU for the test EPROM

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