Random, hard-to-pin-down faults: resets, missing voltages or devices dropping out.

Strange intermittent faults from power supply solder joints

Cause: Cracked or cold solder joints at power supply connector J3 (and the other power supply headers), on the fuse board, or at the ground spade lugs under the transformer.

Checks

• Inspect the J3 header pins and the other power supply connectors.
• Check the fuse board joints and the transformer ground lugs.

Fix

• Reflow every power supply connector, the fuse board headers and the ground lug connections.

Unplug the game before pulling fuses or working on the power supply; the transformer side carries line voltage.

Systems

• Bally 6803

Related tips

• Power supply test points and their voltages
• No +5 V at TP1 or no 14 V at TP5
• +5 V still bad with good C1 and diodes
• No 43 V for the coils
• Replacing the 78H05 +5 V regulator
• Bad +5 V bridge diodes D1-D4
• Check every power supply fuse before first power-up
• Turn the display voltage down to 170 V

Source: Repairing Bally 6803 Pinball Games from 1985 to 1989, Clay Harrell (pinrepair.com)