I recently encountered the rather common "1 coin overpay" problem with my
historically rather troublesome Bally 891-20 Super Continental.
"Not a problem," I thought. "I've seen lots of threads about this at the NLG forum, so it's probably an easy fix."
Of course not.
Short version of the solution: If checking everything else doesn't fix it, check to see if the wipers are properly mounted to the spiral cam.
Also check to see if the 100 tooth gear or its shaft are cracked. (see below)
After realizing that everything was overpaying by one, I looked at every thread that I could find on this site about overpays in general and the "overpay by one" problem specifically.
I discovered that my rubber zero stop had disintegrated, so I replaced it. Then I thought it would be a simple matter to adjust the stop so that the zero switch reset at zero and that the wipers were correctly adjusted so that they'd step off of the traces at the appropriate time.
I'd put a lead of my meter on the F on the payboard and the other on the 2, and manually advance the counter two steps. It should have continuity at zero, and after the first step, and at the second step, the circuit should open.
That wasn't happening; the circuit wasn't opening until the
third step. So i lowered the rubber stop to move the stop point just enough so that the wiper would step off at the second advance of the counter.
To get it to do that, I had to lower the rubber stop so far down that the zero switch wouldn't ever open.
I put it aside for a couple of weeks and just gave it a rest.
This week, I looked at it with fresh eyes, still couldn't find anything wrong, and just decided to take the entire assembly apart and see what it looked like on the
back side of the spiral cam.
And then I found the problem.
Unlike many Bally machines, this particular machine has a
plastic spiral cam, rather than a metal one. The wipers attach to the cam using two screws, and they're aligned by two plastic buttons or tabs on the cam that fit through two holes in the wiper arm. You mount it so that he buttons go through the holes, and then you tighten the screws.
The problem, in my case, was that the lower button had broken off. That's not a problem if the arm is properly aligned
and if the screws are tight. But if the screws should work just a little bit loose, it's possible to get some lateral movement in the wiper arm.
It doesn't take much to get it out of alignment
just enough so that it won't quite step off the trace properly when advancing.
I could see where the button used to be and aligned it by sight. I tightened the screws down and put a small dab of hot glue in the hole where the button used to be. The machine started paying correctly.
Tip: It's
really easy to overtighten those screws and that will cause the spiral cam to crack.
The plastic spiral cams seem to be relatively uncommon, and as such, this shouldn't be the first thing to check if your Bally slot is overpaying by one. But I thought I'd share this, as I didn't see this particular issue mentioned in any of other threads on the topic.
At some point, I should probably just replace the cam. Then again, this may work properly for years to come.
The plastic spiral cam probably wasn't Bally's best idea.