Quoted from newovad:
I feel your pain. It happens on my game. It happened with the original trough and it still happens with the updated opto trough. I'm assuming it has to be an issue with the release coil. Mine only happens during System Failure. I'm on the 6.0 code.
I have a couple ideas. First of all I will try and explain the way that I understand the problem and if I get it wrong, please correct me and we will go from there.
1. In certain conditions the Trough ball Lock is not releasing the balls into the VUK to be kicked into the lane. It seems that the conditions for both of you may be slightly different.
2. The VUK will keep firing even though there is no ball there.
I am just going to start throwing ideas out there based on my experience. None of it may help but we are going to give it a shot.
First of all there is a spacer between the playfield and the Trough Ball Lock (TBL). I cant 100% say that is it factory because it is not mentioned in the parts manual but my game will not function without it. I wonder how I know that.
Without that spacer installed, There is not enough room for the ball to pass to the VUK. Now a old tired mech with work out parts and a worn coil stop may allow a ball to pass without it installed. I think one of you mentioned that its when the trough is nearly empty that the TBL will not feed. Lets say that when the TBL fires, there is just a small amount of contact but there is enough "push" from the balls behind it heading downhill that the ball will go trough. When there is no push, the ball may not make it through.
By the same token, If there is just enough contact, the problem may happen sometimes and not others.
As far as the VUK firing with no ball. That sounds like the VUK switch activating and that can happen.
I have a question: Is the TBL firing constantly like the VUK or does it just fire once to release the ball and then the VUK keeps firing?
On your switch test, How much movement does it take for the VUK switch to activate? If it is so close to the edge that just touching it makes it activate then a coil firing can create enough vibration for the switch to activate.
Well just throwing some ideas out. If I got some information wrong let me know and I will try and help some more.