Check the AC power input connectors too

While doing the GI plugs, also repin the driver board's AC inputs, which can cause random resets: J101 (J129 on WPC-95), 7 pins, the 9 and 13 V AC feeding +5 and +12 V; J102 (J128), 9 pins, 16 V AC; and J112 (J127), 5 pins, 9.8 V AC. Replace header pins as well as plug pins and check the through-holes.

Systems

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

Related tips

• GI connectors on the driver board
• GI string dead with a scorched connector
• GI out because the GI connector burned
• Repair a burnt GI connector on the driver board
• Lamp matrix connectors on the driver board
• Backbox GI out while flashers work: burnt connectors at J120 and J121
• Resets from worn power connectors between transformer, driver and CPU boards
• Coils pulse and backbox flashers too bright: flasher power wire on J132

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