My Mars Trek has developed a new problem. Sometimes the ball doesn’t end when it drains into the outhole. I can open the coin door and see that the outhole switch is closed (I can even make sure by pressing my finger on it), but the machine won’t advance to the next ball, and the ball won’t kick out.

Slapping the lockdown bar gets the ball to end and eject to the next round (you can guess how I figured that out), and a tap on the middle of the play field - with the glass off- does the same thing.

I cleaned the outhole switch with a flex stone, but that didn’t solve it. Adjusting the switch didn't help, either.

To check the switch, I waited for a ball to “fail” (just sit there in the outhole), and I shorted the switch with a jumper wire - touching the two soldered points. That also didn’t make the ball eject. The ball just sat there. But when I slapped the lockdown bar, the ball ejected….

I tried jumping the switch again when it was open (without a ball activating it), and the eject mechenism fired.

Why would slapping the machine make the switch fire, when jumping the switch won’t activate it?

Thanks for your time, any advice would be appreciated.

I tried the 600 grit sandpaper, but the symptom is the same. Thanks for the reply, though.

Again, thanks for the replies.

I had a friend mention the bonus counter that activates after each ball. I think that's my problem. When the ball just sits in the outhole, the counter isn't in the zero position. I gently encouraged a spider arm into the right position, and the game advanced. Maybe that's what what I was moving when I slapped the machine?

I lightly sanded (600 grit) underneath all the spider arms and the brass connections on the bonus unit. I also applied a thin coat of Super Lube. It seems to have solved the problem, but I'll report back after several more games.

I haven't had a problem with a ball ending in the last 50 balls. It was failing about every third ball or so. I think I can call this fixed.
Thanks for the input!