Watching the supplies while the game resets

Steps

• Use a meter fixed to one range (not autoranging), or a scope.
• Watch TP2 (+5 V) while making the game reset; it should not change at all.
• Watch TP4, the zero-cross signal; it should also stay steady.
• On the CPU board watch U10 pin 1, the MC34064 reset output; if it drops below about 4.7 V when the flippers fire, it is forcing the resets. Work back from there to the failing part.
• If reseating a connector stops the resets, replace both its header pins and housing pins.

Systems

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

Related tips

• What a WPC game reset is
• Factory settings restored at every power-up after new batteries: do a factory reset
• Raising the WPC/WPC-S +5 V to about 5.15 V (last-resort reset fix)
• Resets remain after rectifiers, caps and connectors are done
• Resets and GI that will not dim after BR2 was replaced
• Resets continue although the bridge and diodes test good
• Resets: +5 V at the driver board test point is low
• 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)