The game resets after running a while, or the +5 V is high, low or wandering.

+5 V wrong or drifting; resets after a few minutes

Cause: The 500 ohm R3 trimmer on A2 wears out: it can short and push well over 5.2 V into the logic, or open and leave less than the 4.9 V minimum.

Checks

• Measure +5 V at the CPU board A1P1 (pin 1 to pin 4) over time.

Fix

• Replace R3 with a good-quality 500 ohm trimmer and set the voltage again.

Systems

• Gottlieb System 3

Related tips

• How the A2 +5 V supply works
• A2 has no overvoltage shutdown
• Checking and setting +5 V at the CPU board
• A2 and A3 plug wire colours

Source: Repairing Gottlieb System 3 Electronic Pinball Games from 1989 to 1996, Clay Harrell (pinrepair.com)