Two switches on the mini playfield don't work properly (one reads closed while open), and pressing a third mini playfield switch briefly shows the subway opto switch before its own number.
Mini playfield switches misread and one switch shows as another: bad diode and miswire
Cause: A bad switch diode let current flow backwards through the matrix, causing phantom closures across switches that share rows and columns, and a wire on the mini playfield had been connected to the wrong place by a previous owner.
Checks
- Map the affected switches on the matrix chart: phantom readings usually involve switches at the corners of a rectangle of rows and columns.
- Test every diode on those switches with the diode meter setting and look for diodes bent onto lugs or brackets.
- Check the microswitch under the mini playfield above the saucer, which the ball often hits and can crush its diode into the wires.
- Compare each wire on the mini playfield switches with the manual's wiring.
Fix
- Replace the bad diode and reconnect the misplaced wire as the manual shows.
Systems
Games
Related tips
- One switch also triggers others in its column: bent diode on the mini playfield
- Indiana Jones ninth switch column
- Ninth switch column on Twilight Zone, Indiana Jones and STNG
- A whole switch column dead or all closed
- A whole switch row dead or all closed
- Whole switch column dead after a diode went in backwards: column driver chip
- Reading WPC switch numbers and the switch test display
- Slam tilt every game and random switch hits: bent switch diode
Source: Pinball Repair help group!! (Facebook group)