Resets mostly in the first minutes after switching on.

Resets when the game is cold: the power box thermistor

Cause: The thermistor in the power box behind the coin door limits inrush current and should drop to almost zero ohms once warm. A worn one stays resistive and holds the line voltage down.

Checks

• Game on and warm (about a minute), in attract mode: AC across the thermistor should be no more than 1.00 V (up to about 5 V right after power-on is normal).
• Game unplugged and cold: it should read no more than 2-3 ohms.
• Temporarily bridge it with a clip lead and see if cold resets stop.

Fix

• Replace the thermistor, an 8 A 2.5 ohm current limiter (CL30 type). It is the gray disc between the line filter and the fuse; do not confuse it with the green MOV across the line filter.

The power box carries 115 V AC (220 V in Europe); unplug the game before working in it.

Systems

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

Related tips

• Factory settings restored at every power-up after new batteries: do a factory reset
• Random resets after a full 5 V rework: bad J130 connector on the power driver
• After a power cut: resets, then won't serve a ball
• What a WPC game reset is
• Game keeps resetting during play: poor J101/J102 power connections
• Watching the supplies while the game resets
• WPC CPU board LEDs at power-on

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