Slam tilts, or slingshots, magnets, pop bumpers or flipper hold fire on their own, often worse with many feature lamps lit.

Random coil firing or slam tilt from weak 12 V (notably Theatre of Magic)

Cause: The switch matrix 12 V is sagging from a weak BR1, cracked traces around BR1 or a weak 7812 regulator.

Checks

• Unplug J133 to disable the controlled lamps and see whether the fault stops.

Fix

• Rebuild the 12/18 V section: BR1, C6, C7 and Q2 (7812), and add the BR1 jumper wires.

Systems

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

Related tips

• Driver board supply test points and normal readings
• One switch triggers others and flippers act oddly: drop target switch wired backwards
• Row or column "ground short" errors
• Game accepts no coins and will not start
• Slingshot also fires an outlane magnet: ribbon cable not fully seated
• Two or more coils fire together
• Kicker dead in coil test plus a lamp row and column out: reseat the CPU to driver ribbon
• Resets or dead banks of coils or lamps from cracked bridge or cap solder

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