Odd, intermittent faults across several boards.

Erratic faults from a poor ground at the A18 board

Cause: Boards sit on nylon standoffs with no metal ground plane, so ground travels through connectors to the A18 board on the transformer frame. Those connectors crack at their solder joints and the ground level drifts above zero.

Checks

• Inspect the four connectors on the A18 board for cracked solder joints.
• Measure resistance from board grounds to the transformer frame.

Fix

• Reflow the A18 joints and apply one of the ground fixes.

Systems

• Gottlieb System 3

Related tips

• Ground fix: tie each ground plug's wires together
• Bulbs burn out fast: 110 V jumper plug fitted
• DC supplies from the transformer panel
• AC windings from the transformer
• Boots to game over, then lamps and switches are dead
• A12 transformer panel fuses F3 to F7
• A12 transformer panel fuses F8 to F11
• Game won't boot: failed vertical fuse holder

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