WPC switch matrix basics

Playfield switches sit in a matrix of eight columns and eight rows (64 switches). Twilight Zone, Star Trek: The Next Generation and Indiana Jones add a ninth column for 72. Flipper, EOS and coin-door test switches are dedicated inputs outside the matrix. A switch held closed for a coil (a pop bumper switch, say), is ignored by the CPU, so the device stops working.

Systems

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

Related tips

• How the switch matrix reads a switch
• How the Williams switch matrix is scanned
• Switch matrix chips on the CPU board
• Checking the switch matrix with a logic probe
• Reading WPC switch numbers and the switch test display
• Narrowing a switch matrix fault to the CPU board, wiring or opto boards
• Using the switch edge test
• Switch 24, the always-closed switch

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