Checking GI triacs with the game on

Steps

• Put the game in the GI test with all strings at full (level 8).
• Meter on AC, black probe to ground.
• Probe the tab screw of each triac heat sink in turn: about 1 V AC or a little less means that triac is switching.
• Feel each heat sink; a cold one is not switching on. Usually the cause is the J115 input connector, the fuse or a broken trace, not the triac.

Systems

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

Related tips

• One GI string dead though the board and fuse test fine: burnt connector in the cabinet
• GI string still dead after replacing J115: broken through-hole, add a jumper
• One GI string dead after a restoration: unkeyed J115 plugged in upside down
• Several GI strings dead after a connector repair: lifted pads at J115
• All GI out (playfield and backbox) with good fuses and plugs: reseat the CPU ASIC and ROM
• All backbox lights out with good fuses: burned J120 GI connector
• A whole string of backbox lamps is out: blown GI fuse F110
• Two GI strings still dead after fixing a burnt J120: broken pads and traces

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