Decide whether a phantom switch is in the playfield or the CPU board

Steps

• Put the game in switch edge test.
• Unplug 1J8 and 1J10 from the CPU board.
• Find the row and column of the switch that shows the phantom closure.
• Bridge that row pin and column pin directly on the CPU board headers with a clip lead (see the 1J8/1J10 pin lists).
• If the phantom switch does not appear, the fault is in the playfield wiring; if it still appears, the CPU board is at fault.

Systems

• Williams System 11
• Williams System 11A
• Williams System 11B
• Williams System 11C

Related tips

• Row or column error: CPU board or playfield?
• Fixing a dead switch column on the CPU board
• Fixing a dead switch row on the CPU board
• Random slam tilts: replace the SRC6 resistor pack on the CPU board
• How the Williams switch matrix is scanned
• Testing the switch columns with a clip lead
• Testing the switch rows with a clip lead
• Testing the switch matrix with a logic probe

Source: Repairing Williams System 11 Pinball 1986 to 1990, Part Three, Clay Harrell