Quoted from ZoraShinoda:Okay I'm really confused with this right opto issue. It'll work for a little bit and then it will stop working.
This time when it stopped working I removed it from the playfield and went into switch test passed my finger between the opto pieces and I would break the beam and the light would go out on the receiver however it would not register for the switch test.
Would love to hear any ideas if anyone has them
Check out Section 11.3 Troubleshooting Switches (pg34) of Stern's Spike System Manual (downloadable from the Stern website) - this shows the steps in troubleshooting & diagnosing a switch related issue if you have either a multimeter or a jumper cable.