What a WPC game reset is

A reset looks like the game switching off and back on, usually during play when the flippers fire. The MC34064 watchdog at U10 on the CPU board restarts the CPU whenever +5 V dips below about 4.7 V. Heavy 50 V flipper current stresses aging 5 V parts, the 5 V sags and the game reboots; in bad cases it loops on and off and never starts. It is most common on 1990-1995 WPC through WPC-S games and much less so on WPC-95.

Systems

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

Related tips

• Dead CPU: check the reset and IRQ lines
• Raising the WPC/WPC-S +5 V to about 5.15 V (last-resort reset fix)
• Watching the supplies while the game resets
• Raising the WPC-95 +5 V to about 5.2 V
• WPC CPU board LED meanings
• WPC CPU board LEDs at power-on
• Resets: +5 V at the driver board test point is low
• Factory settings restored at every power-up after new batteries: do a factory reset

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