How the always-closed switch 24 is wired

Switch 24 is not a real switch: a wire loop runs from CPU connector J212 to coin door interface board connector J3, where column 2 and row 4 are joined through a 1N4004 diode (band toward column 2). A loose J212 or J3, or broken wiring, gives the fuse error. This is a rare cause.

Systems

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

Related tips

• Switch 24, the always-closed switch
• A whole switch column dead or all closed
• A whole switch row dead or all closed
• Using the switch edge test
• How the switch matrix reads a switch
• How the Williams switch matrix is scanned
• WPC switch matrix basics
• Switch matrix chips on the CPU board

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