Finding a switch wiring short to ground

Steps

• Confirm the CPU board passes the row and column tests, so the fault is in the wiring.
• Go to the far end of the affected row or column wire under the playfield; switches are daisy-chained.
• Break the chain one switch at a time while watching switch test.
• The short is at the switch where the fault disappears.

Systems

• Williams System 9
• Williams System 11
• Williams System 11A
• Williams System 11B
• Williams System 11C

Related tips

• Standard switch and diode wiring
• A bad SR14 can short switch rows on System 11A and later
• Find the short before refitting a repaired CPU
• Using the System 11 switch tests
• System 11 switch matrix differences
• Entering the System 11 switch tests
• Testing a leaf switch diode in place
• Testing the switch columns with a clip lead

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