The game boots to attract mode but the red self-test button in the coin door has no effect.

Self test will not start from the coin door button

Cause: The test button, its wiring, the coin door connector or MPU connector J3; if a direct short does not work either, the MPU board.

Checks

• Short MPU J3 pin 1 to ground. If diagnostics start, the fault is in the button, coin door wiring or J3 connector.
• If shorting J3 pin 1 does not start the test, look for an MPU board fault.

Fix

• Repair the button, wiring or connector, or repair the MPU board.

Systems

• Bally MPU AS-2518-17
• Bally MPU AS-2518-35

Related tips

• Coin door switch shorted to ground causes lamp and other odd faults
• Player 1 display shows credits and ball in play
• Odd switch problems from corrosion at the DIP switches
• Bally switch matrix: 5 strobes by 8 returns, numbered 1 to 40
• Some games add a sixth switch strobe ST5 (switches 41-48)
• MPU switch connector pins J2 and J3
• Prove the MPU switch inputs with the harness unplugged
• Switch matrix confused by a bad MPU DIP switch diode

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