Williams System 11 (SoF) occasionally serving a ball when it shouldn't

[Fubar]

My SoF does this thing where occasionally a ball pops in the shooter lane when it shouldn't. Usually right as a ball has drained, before the bonus countdown starts. Then I can carry on playing my ball but there's no music - clearly not intended.

I'm 99% sure it's caused by the ball that just drained being pushed over the trough's hump a bit too hard, and knocking its buddy over into the lane.

Before I start fiddling - is this a common issue? Is there a known fix? Doesn't seem to be anything about it on pinwiki...

(Seems like the game also likes to leave a ball in the shooter lane in attract mode, but I think that's intentional...)

 

[DRD]

Sorry if daft but does it have the correct number of balls in it?

Check the ball drain coil type versus what the manual says should be in there

I would then look at the ball trough switches. Problems with these can cause issues like yours.

Ball trough switches might fail to be properly triggered, or fail to release "quickly" when the ball has gone

 

[andy]

(Seems like the game also likes to leave a ball in the shooter lane in attract mode, but I think that's intentional...)

I don't think it is....I don't remember my SOF doing that.

My vote is the trough switches, as @DAD says flaky ones can definitely cause issues like this

 

[Fubar]

Thanks @DRD and @andy for the tips, appreciate it

Sorry if daft but does it have the correct number of balls in it?

There are no daft questions Yes it has 3 balls installed which is correct for this game.

Check the ball drain coil type versus what the manual says should be in there

Both trough coils are AE-23-800, which matches the manual. From experimenting with the apron off, when the drained ball gets pushed through the trough, the first ball (about to be ejected) does do a little jump, but that doesn't seem strong enough to push it into the shooter lane now that I've had a good look.

Another issue which has sometimes happened to me (again, very rarely) is that first ball failing to be served, but instead wedged slightly above its resting place in the trough (high enough not to trigger its switch). I could always solve this by shaking the machine, but then lost my ball as the game thought I'd drained

I would then look at the ball trough switches. Problems with these can cause issues like yours.

Ball trough switches might fail to be properly triggered, or fail to release "quickly" when the ball has gone

That does sound like the most likely culprit now. I checked the wiring and diodes, and nothing seems amiss. Of course, the issue is sporadic and I've not been able to reproduce it today, even after playing a number of 4 player games with the apron off, where I'd just move the ball from the shooter lane to the drain...


I'm trying to understand what would cause the game to eject a ball, in particular when it boots. If it detects all balls in the trough it should be happy. If any balls are missing however, I can't see how firing the trough eject call helps. As I said, when this bug does occur, it's only when a ball drains or when the game boots (and maybe in attract mode after game over - not sure).

 

[Fubar]

After many games, I concluded that it was a mechanical issue where the drained ball is kicked along the trough too hard and knocks the front one out.

Fixed by sticking some foam against the edge of the playfield for the front ball to rest against. The front ball is visibly less jostled than before, and it doesn't affect the normal eject function at all