Switches under a resting ball (ball trough, lock, kickout hole) register intermittently.
Unreliable switches where the ball rests (trough, locks, kickouts)
Cause: A factory assembly error on games up to about Black Knight: one leaf blade was fitted backwards, so a gold contact meets a plain rivet instead of another gold contact. Low-voltage switch matrix contacts need gold on gold.
Checks
- Look at whether the two contacts face each other gold to gold.
Fix
- Split the switch stack at the spacers and turn the wrong blade round.
- For Firepower and Black Knight, Williams offered microswitch ball trough retrofit kits.
Systems
Related tips
- Unreliable switches where the ball rests (trough, lock, kickout)
- A ball resting on one switch stops others in its column
- Drop target switches also trigger the eject hole: column jumper on wrong switch
- Switch wire broken off near the trough: it goes on the diode's non-banded (anode) end
- Switches stuck on: board or playfield?
- A drop target switch registers when the lower pop fires: replace the pop coil
Source: Repairing Williams System 3 to System 7 Pinball 1977 to 1984, Part Three, Clay Harrell (pinrepair.com)