Testing an MPU in the game with only J4 connected

If the game's own power supply is known good, an MPU board can be checked in the cabinet with just its J4 plug connected, since J4 carries all of the board's power. The other MPU connectors can stay off while you count the LED flashes.

Systems

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

Related tips

• 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
• Telling a -17 MPU from a -35 by connector J5

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