Test GI outputs on the driver board

Steps

• Unplug J119, J120 and J121; power on with the meter on AC volts.
• Each string should read 6.3 to 7.3 V AC between: J120-1 and J120-7 (string 1, Q18, F110); J120-2 and J120-8 (string 2, Q10, F109); J120-3 and J120-9 (string 3, Q14, F108); J120-5 and J120-10 (string 4, Q16, F107); J120-6 and J120-11 (string 5, Q12, F106). String 5 also appears on J119 pins 1 and 3. J120-4 is the key.
• To test a triac, measure from its center leg (the tab) and its left leg against the string's return: 6.3 V AC should be on the left leg. None means the triac is bad; present means a burnt connector or broken through-hole between triac and plug.

Systems

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

Related tips

• Testing lamp-row drivers with a test lamp
• Testing lamp-column drivers with a test lamp
• Where GI power flows on the driver board
• WPC lamp matrix and GI driver parts
• J115 GI input pin map (WPC-89/WPC-S driver board)
• GI fuse keeps blowing: isolate driver board or wiring
• GI string dead after connector replacement: broken traces
• Several GI strings dead after a connector repair: lifted pads at J115

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