I'm adding my 2 cents to this chain as well. I had an issue with the Wipe Out starting gate working intermittently. The machine would play fine for weeks, then balls would get stuck at the top of the starting gate for weeks. Then it would work. Then it wouldn't. Opto switch tests worked fine in test mode. Ultimately, it came down to needing to reflow the solder points on each side of the bracket with the opto sensors. This became very easy to address once I started looking at the 4 LEDs on the quad opto board under the playfield. From time to time D4 LED was lit, indicating the starting gate opto had a broken laser, or something was present...when something wasn't. I removed the bracket and opto sensor assembly from the starting gate, flipped up the playfield, reconnected the 4pin harness under the playfield so that I could now play with the opto sensor and see the quad opto board together. When I put my finger in the opto, the LED would be lit - as expected. As I jostled the sides of the opto sensor bracket where the solder pads are, the LED on the board would be intermittent. It was obvious that the solder joints were not solid. In particular, I was actually able to jostle each solder joint individually and see it's impact on the LED on the opto board. I knew the issue then were the two solder points of the opto sensor on the left side. I reflowed those two points. BAM. back in business. To the point made by Sonic , I went a step further to just reflow the 4 solder points on each side of the opto bracket, clean the opto with alcohol - and good to go.