The jumper test passes but a row or column misbehaves, or phantom switches close.
Row or column fault on the playfield
Cause: A switch shorted to ground (solder splash, wire crushed between playfield and cabinet), a reversed switch diode, wires pulled out of the playfield connector housings, or a shorted/open 1N4004.
Checks
- Look for solder splashes and crushed wires.
- Check each diode in the row/column is the right way round.
- Check the connector housings where the playfield plugs in.
- Diode-test suspect diodes (one lead freed: 0.4-0.6 one way, nothing the other).
Fix
- Clear the short, refit the diode correctly, or re-pin the connector.
Systems
Related tips
- Test the switch column drivers with a diode jumper
- Test the switch row inputs with a diode jumper
- Testing CPU switch rows and columns with a diode and clip lead
- False switch readings only when several switches are closed
- Strange behaviour across a whole row or column from a switch diode
- Switch row (return) circuit on the CPU board
- Lamp lights twice or two lamps act as one
- Lamps in a row or column light twice per sweep
Source: Repairing Williams System 3 to System 7 Pinball 1977 to 1984, Part Three, Clay Harrell (pinrepair.com)