Switch diode failures and what they look like

Every playfield microswitch carries a 1N4004 diode. A shorted one, which is uncommon, makes its whole row or column misbehave when other switches close; an open one means that switch never registers.

Systems

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

Related tips

• Testing a leaf switch diode in place
• Fitting a new switch diode the right way round
• Testing CPU switch rows and columns with a diode and clip lead
• Testing a microswitch diode without unsoldering it
• System 80 switch matrix diodes
• Spare diodes for coils and switches
• Test the switch column drivers with a diode jumper
• Test the switch row inputs with a diode jumper

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