I've got something weird here. I just finished a restoration on a Diner. The slings fire at random and it has me baffled. It does seem to happen when I push the flipper buttons and is more likely if both flippers are done at the same time. Occasionally a pop bumper triggers it.

The switch gap isn't too close so that's not the cause.

I've tested the switches in the switch test and nothing is triggering other switches.

The coil test is fine as well.

When I put it all back together, I inserted the interconnect board connector backwards that supply's the 12v to the drop target option boards. It fried the lm339 chip on one opto board and is fixed.

Any ideas what may be causing this phantom firing? Thanks!

Figured it out. The other lm339 were "working" but throwing out dirty signals to the matrix.