Switch 24, the always-closed switch

Every WPC game has an always-closed switch, usually switch 24 (column 2, row 4), held closed by wiring on the coin door interface board through J212. If the CPU sees it open it assumes the matrix has failed, for example from lost 12 V. Unplugging J206-J209 or J212 for testing can trigger the error until all connectors are back and any blown F115 (F101 on WPC-95) is replaced.

Systems

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

Related tips

• How the always-closed switch 24 is wired
• Using the switch edge test
• A whole switch column dead or all closed
• A whole switch row dead or all closed
• 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 Two, Clay Harrell (pinrepair.com)