The game resets, often in summer or when sharing a circuit with a heavy appliance.

Resets caused by low wall voltage

Cause: Low line voltage. As little as 112 V AC can cause resets; Twilight Zone often resets below about 117 V.

Checks

• Measure the outlet with the meter on AC volts: it should be 115-120 V.
• A WPC game draws up to 8 A; keep to no more than two games on a 15 A circuit, and avoid circuits with air conditioners, fridges, dehumidifiers or sump pumps.

Fix

• Move the game to a better circuit.
• As a last resort, rejumper the transformer for low line or raise the 5 V supply to 5.1 V (see the 5 V adjustment entries).

Line voltage is present in the cabinet and backbox with the game on; keep hands clear of the transformer and power wiring.

Systems

• WPC Alpha-Numeric
• WPC Dot Matrix
• WPC Fliptronics
• WPC DCS
• WPC-Security (WPC-S)
• WPC-95

Related tips

• Pre-WPC-95 resets: replace BR2, C5, C4 and the J101 pins together
• WPC-89 resets on low +5 V: replace the small 100 uF 5 V filter caps
• What a WPC game reset is

Source: Repairing Williams/Bally WPC Pinball Games from 1990 to 1999, Part Two, Clay Harrell (pinrepair.com)