Closing one switch also registers others.

Two or more unrelated switches trigger together

Cause: A shorted switch diode, a switch lug touching metal, or a solder short in the CPU switch circuit.

Checks

• Test the diodes on the switches involved.
• Look for switch lugs touching metal parts.
• Inspect the CPU switch area for solder bridges.

Fix

• Replace the diode, bend the lug clear, or clear the solder bridge.

Systems

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

Related tips

• A switch does not register in the switch test
• One switch does not work
• One switch also triggers another: corroded switch connector on the CPU board
• One switch also triggers others in its column: bent diode on the mini playfield
• Phantom switch closures: one switch triggers something unrelated
• Most of switch row 6 dead, last switch works: broken row wire
• Spinner stops registering: broken wire on an upper flipper EOS switch
• Several switches in one row or column dead: a broken daisy-chain wire

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