FYI: Bally 891-20 1 Coin Overpay Tip

[essmeier]

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.

[DavidLee]

This is good to know.


Probably fixable by drilling the cam at the B pin.
Then re-construct the pin with JB weld.


Or eBay.

[Amechanic]

Thanks for the fix tip...

[essmeier]

I looked into drilling it, but there's business going on on the other side of that missing pin and I don't want to interfere with the cam's operation.

I'll bet this is a good place to use Bondic. It's liquid plastic that sets with exposure to UV light.  Don't have any at the moment, but it's probably what's needed here for long-term repair.

Or I can keep an eye out for another cam.  Like I said, now that it's adjusted and tight, it might work well for years.

[Herbie21]

with the one coin overpay I also always look at the position of th backalite pay-out board, it can be a bit loose, position the board, maybe slightly move to the left, in the case of one overpay and fasten the two bolts


Herbie

[DavidLee]

It’s possible the finger contacts aren’t riding off the metal receiver strips soon enough.
Allowing one more coin to be ejected.


Test this by manually stepping up the unit to 10, 14 times then check for continuity.
There should not be any between the contacts and the metal strips.
If there is, then further investigation and most likely a small adjustment to the cam stop.

[essmeier]

It’s possible the finger contacts aren’t riding off the metal receiver strips soon enough.

The problem on my particular machine was that the wiper was misaligned due to the button being broken off of the spiral cam and the screws becoming loose.   

I created this thread to share that possible cause as I hadn't seen it mentioned in other threads about the "one coin overpay" problem.

[essmeier]

Just an update regarding this one-coin-overpay problem.

I went ahead and purchased a new spiral cam that I found on eBay.  While taking the entire thing apart, I discovered a spiral crack in the main shaft of my 100 tooth gear.  The crack did not prevent the unit from working.  Had I not taken the unit apart to replace the spiral cam, I might have missed it.

That crack is there in such a way that it will twist open while the shaft is advancing.  That could also have affected the payout, as it could have the gear and the wipers out of position relative to one another.

While replacing the spiral cam and the 100 tooth gear, I either broke or discovered a break in the microswitch on that mechanism.

So, I've now replaced the gear, the cam, and the switch, and payouts seem OK now.

Bottom line?  These are old machines that had heavy, continuous 24/7 use; look for worn out plastic parts on the pay unit.

[DavidLee]

Thanks for sharing, good advice.