Closing one switch fires an unrelated coil, tilts or scores something else, or many switches read as the same switch in switch test.
One switch triggers an unrelated switch (phantom closures)
Cause: A shorted switch, usually an above-playfield switch bashed together by an airborne ball, or a shorted switch diode.
Checks
- With the glass off, start a game and press switches by hand to find the one that causes the phantom event.
- Look up its row and column, then list the other three switches that form a square with it. Example: for switch 53 (column 7 row 5) check 39 (column 5 row 7), 37 (column 5 row 5) and 55 (column 7 row 7).
- The shorted switch is usually one of those four.
Fix
- Separate or replace the shorted switch, or replace its diode.
Systems
Related tips
- Playfield switches fire coils and switch columns misread: failed column driver Q44
- Pop bumper fires only now and then: clean and gap its skirt switch
- Random switch closures, random tilts or slam from bad resistor networks
- Decide whether a phantom switch is in the playfield or the CPU board
- Knocker fires several times at power-on with a switch number shown
- Instant tilt and scrambled switch test: burnt resistor networks on the CPU
- Catapult sometimes throws the locked ball early: clean or replace its switch
Source: Repairing Williams System 11 Pinball 1986 to 1990, Part Three, Clay Harrell