Use a flashlight to test an opto receiver
In switch edge test, shine an ordinary flashlight into the receiver; the switch should change. If the flashlight works the receiver but the game's own transmitter does not, the transmitter or its supply is bad.
Systems
Related tips
- Glue new-style optos down
- Millionaire was the first Williams game with opto switches
- Opto switches dead all at once
- System 11B opto board fails with good optos
Source: Repairing Williams System 11 Pinball 1986 to 1990, Part Three, Clay Harrell