A row wire on the wrong end of a switch diode creates ghost switches

If a switch's row wire is on the wrong end of its diode, closing it together with another switch on the same column and a third on its own row makes a fourth switch show closed. Example: with r3c3 miswired, closing r3c3, r2c3 and r3c6 also shows r2c6.

Systems

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

Related tips

• Testing CPU switch rows and columns with a diode and clip lead
• Testing a switch diode out of circuit
• Most of switch row 6 dead, last switch works: broken row wire
• "Ground Short Row" message
• "Row Short" message
• Several switches in one row or column dead: a broken daisy-chain wire
• Switch diode failures and what they look like
• Testing a leaf switch diode in place

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