Random resets or intermittent faults on a game with the -54 supply.

Resets on Xenon and later from leaky -54 logic diodes

Cause: The four separate diodes that rectify the logic supply run hot and leak, letting AC ripple into the +5 V.

Checks

• Measure AC ripple across C23 on the solenoid driver board.

Fix

• Replace the four diodes with 6 A types: 6A50 or higher-voltage 6A2/6A200/6A4. Avoid 1N4004/1N4007, which are only 1 A.

Systems

• Bally MPU AS-2518-35

Related tips

• Quick test of reset transistor Q1

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