Random scoring, random tilts, the slam switch tripping by itself or generally odd switch behaviour, with the fault on the CPU board.

Random switch closures, random tilts or slam from bad resistor networks

Cause: A failed switch-matrix resistor network (SIP), most often SR9, SR10 or SR11. F-14 Tomcat is especially prone to this.

Checks

• Measure SR9, SR10 and SR11 with an ohmmeter (they test reliably in circuit).
• Check SR3, SR15, SR17, SR14, SR8 and the SRC6 resistor/capacitor pack as needed (see the network reference entries).

Fix

• Replace any network that reads wrong or "strange".

Systems

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

Related tips

• Random slam tilts: replace the SRC6 resistor pack on the CPU board
• Switch matrix resistor networks and their values
• Testing a resistor network with a meter
• Replacing SRC6 with a plain bussed resistor network
• 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
• Every switch shows active, even with the switch plugs removed: failed PIA at U38

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