Does anyone see anything obvious missing here, like a spring? It's acting like it's missing one: when it tries to add a credit it catches a bit, but skips, and rather than decrementing one at a time, it just releases and goes back to 0. Everything moves smoothly, and I've tried to compare it to another I have, but I haven't yanked that one for a good look. Somebody did mess with it at some point, because the spring was on the wrong side of one of the pins.
![IMG_1028[1] (resized).JPG](data:image/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==)
IMG_1028[1] (resized).JPGBoth of the longer arms driven by the solenoid plungers have shorter arms that engage the gear teeth. Each one should fall into the gap between teeth as its longer arm activates. The one on the advance arm falls into the gap and pushes the tooth forward. The one on the subtract arm falls into the gap to keep the gear from rewinding more than one step.
If that's not working reliably it could be that the shorter arms are worn (so they drop into the gap but work their way out), or that they're not swinging freely on their pivots (so they don't drop into the gap completely). If they're not swinging freely the shoulder bolt could be too tight or they could be bound up with dirt, grease and grime. A little dental floss and your favorite cleaner might help clean that out.
If you do remove the arms, be careful with the shoulder bolts. They're notorious for shearing right off. You'll have better luck removing the nut and lock washer from the back of the frame first before trying to back out the shoulder bolt.
For those unfamiliar, the video at https://www.funwithpinball.com/exhibits/small-boards#CreditUnit shows a closeup of this unit in action at about 0:36.
/Mark
@MarkG-The spring is the only thing that keeps the cog in place? There is about about a half inch of movement in and out on the shaft. When out just a bit it does not engage, and when in place it skips/goes back to 0. Do you know of an exploded view of this stepper anywhere?
Looks like you have a couple other Gottlieb titles in your collection. If they are working, I would have a look at their credit units. You can do an apples-to-apples comparison of their operation to help you learn where this one is malfunctioning.
Quoted from currieddog:The spring is the only thing that keeps the cog in place? There is about about a half inch of movement in and out on the shaft. When out just a bit it does not engage, and when in place it skips/goes back to 0. Do you know of an exploded view of this stepper anywhere?
I didn't realize that the number wheel was off. There should be almost no movement along the gear shaft, in and out through the sleeve. There should be just enough slop to keep things from binding, but not much more.
The diagram in the parts catalogs is pretty busy and hard to make out the motion of the gears. Each of the two short arms should have a spring though. In your photo it's hard to tell if the lower/advance short arm has a spring on it or not. It should look something like this:
Gottlieb step up arm (resized).jpg
The spring should wrap around the hook just below the pivot point. If it's missing that could explain why your stepper resets to zero instead of taking one step back. The lower short arm should prevent the gear from advancing more than one step. Here's a subtract sequence that might help:
Subtract motion (resized).jpg
Working from left to right:
- Everything is at rest.
- The subtract coil (not shown) fires and pulls in its plunger. The top short arm (at 12:00 on the gear) drops into the gap between teeth while the other short arm (3:00) gets pushed out of the way. The gear unwinds a bit, but the short arm at 12:00 keeps the gear from resetting back to zero.
- As the subtract coil relaxes and its plunger starts to retract, the short arm at 3:00 drops into a gap between teeth.
- When the subtract coil and its plunger return to their rest positions, the short arm at 12:00 moves out of the way, but the short arm at 3:00 is in its gap, so the gear can only unwind a little bit more.
- Everything back at rest and the gear has only unwound one step.
Quoted from leckmeck:I would have a look at their credit units.
I have been, but hoped to avoid pulling them completely and removing the cog.
Quoted from MarkG:The diagram in the parts catalogs is pretty busy and hard to make out the motion of the gears.
That part is good. Do you have the rest of the illustration?
Quoted from jeffc:Here is the unit from the 1968 catalog
Thanks! Is that catalog available online?
Hokay, after staring at that gd unit forever, I finally figured out that the cog and arm was moving enough so that the notched piece in post 5 was not catching. With the wheel on and cranked down it doesn't move. Thanks all!!
Quoted from currieddog:Thanks! Is that catalog available online?
Like all Gottlieb docs, it is not available online.
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Springfield, MA