Opto switches in the trough or elsewhere flicker or read wrongly in switch test.
Erratic opto switches from cracked opto board joints
Cause: Vibration cracks the solder joints on the small boards that hold the opto emitters and receivers. Loose surface-mount LM339s on the switch board can mimic an opto fault.
Checks
- Block and unblock each opto in switch test and watch for flicker.
- Inspect the opto board joints closely.
Fix
- Resolder every joint on the emitter and receiver boards.
- If that does not help, check the switch matrix board LM339s.
Systems
Related tips
- How the Capcom switch matrix is wired
- Prove whether dead switches are on the playfield or the switch board
- Reflowing surface-mount chips on the switch matrix board
- Dead switches from failed SIP resistor networks
- Groups of switches dead or intermittent: loose surface-mount LM339s
- Where the boards sit in a Capcom backbox
- Williams trough optos work as Capcom replacements
Source: Capcom Pinball Problems/Solutions