Quoted from dr_spidey:
So I started a game with ramp up. It immediately lowers ramp. Nothing happens. No ball eject. If I manually eject a ball then after twenty seconds sometimes the search starts. But not always.
The fact that the same test does not give the same result every time makes diagnostics difficult. However, based on your information *sometimes* the ball search thread is started even though both balls are in the trough. This can only happen if there is a problem with one or more of the switches (or in the switch wiring, or the switch drivers). Here's what I'd do:
1) Remove both balls, reset the drop targets, ramp and visor to the point where no switch is closed.
2) With switch test running I would gently hit the playfield in various places with my fist to see whether any of the switches is set too tightly.
3) Go through every single switch and close it, verifying that only that one switch is triggered when I do that.
There's another test that you can do: Start a game with the ramp up, one ball in the trough and the other in the shooter lane. The ramp must stay up in this case. If it drops, you have a bad switch. If the ramp stays up, momentarily remove the ball from the shooter lane and put it back. The ramp should drop as soon as the shooter-lane switch closes again.
Finally, if you have problems with the visor switches, this can also prevent a ball from being ejected. However, if that's the case, the ball search thread is not started.