The receiver shows closed in the switch test whether or not the beam is blocked.
An opto shows closed all the time
Cause: Misalignment or dirty lenses.
Checks
- Check alignment of the emitter and receiver.
Fix
- Clean both lenses and re-align the pair.
Systems
Related tips
- How the Sega opto receiver works
- Cleaning optical switches
- Which Sega games use optical switches
- How Sega optical switches behave
Source: Repairing DataEast 1987 (Laser War) to Sega 1995 (Batman Forever), Part Three, Clay Harrell (pinrepair.com)