Proving U6, U9 and U11 in a known-good MPU

The surest test for a suspect CPU, PIA or ROM is to fit it, one chip at a time, in a working MPU and see if that board still boots. Without a spare board, fit new chips and a known good set of game ROMs instead.

Systems

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

Related tips

• 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
• -17, -35 and -133 MPU boards compared

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