Switches under a resting ball, such as the trough, ball locks and kickout holes, register poorly or intermittently.
Unreliable switches where the ball rests (trough, lock, kickout)
Cause: Factory assembly put one leaf blade of each pair on backwards, so a gold-plated contact meets a plain, rough one. Low-voltage solid-state switch circuits are sensitive to this.
Checks
- Look at the contact pair: both contacts should be gold-plated.
Fix
- Turn the reversed blade around so both gold contacts meet, or fit new switch blades.
- Williams offered microswitch ball trough retrofit kits for Firepower and Black Knight.
Systems
Related tips
- Unreliable switches where the ball rests (trough, locks, kickouts)
- 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?
Source: Repairing Williams System 3 to System 7 Pinball 1977 to 1984, Part Two, Clay Harrell (pinrepair.com)