(Topic ID: 194196)

More newbie questions: Weak Stepper Coil


By sraasch

2 years ago



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  • 20 posts
  • 10 Pinsiders participating
  • Latest reply 1 year ago by sraasch
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player unit trouble (resized).png

#1 2 years ago

Hi guys. Your previous answers are much appreciated, so I thought I'd bring my latest dilemma to you as well.

I'm repairing my first pinball (Williams '77 Big Deal), and generally things are going well. One of my last problems has to do with the player unit step-up. Right now, it's working intermittently. I've double-checked and cleaned all the switches in that circuit, and even replaced a wire that I suspected was problematic. But no luck yet.

The coil seems to be "weak". I just found what the resistance *should* be so I'll check that this evening. Right now, the solenoid pulls when it's supposed to, but not enough to advance the unit. By hand, the mechanicals seem to be ok.

I'd appreciate it if anyone can either point me to or provide a brief list of behaviors that you might see in a bad coil. (I'm guessing *this* is one of them).

Also, another question about this coil:
The parts list matches what is in the game (A-22-500), but the schematic shows an A-22-550. Interestingly, I can't seem to find anything other than an A-22-550. In a situation like this, would you normally buy the 550 and remove 50 turns? Does anyone know where I can find the 500.

Thanks!
-Steve

#2 2 years ago

It is unlikely to be the coil.

Have you disassembled and cleaned the unit?

Also replace the sleeve with a new nylon one.

#3 2 years ago

You can also jumper over the switches in that circuit in order to see "full power" vs. power potentially through dirty switches.

#4 2 years ago

Coils generally don't go bad. What you have is insufficient power to the coil itself, or possibly a bad coil sleeve. If the coil goes bad it will be a dead short and blow fuses.

You can get an A 21-500 from Pinball Resource. It will be more powerful than an A 22-550 as it is a bigger gauge wire with fewer turns.

#5 2 years ago

You can verify all the switches are making good contact by taking a resistance reading from the coil lug to the common wire (yellow or black probably) on the far side of them. But none of this matters if the stepper isn't cleaned and moving freely

#6 2 years ago

In EMs, the coil doesn't advance the stepper; it should be done by the return spring. At least on Gottlieb games that was the case. It was done this way because a spring has a known, repeatable force whereas a coil force can vary quite a bit with line voltage.

You can observe this when you operate the unit by hand and watching the behavior as you release the coil plunger. If spring advances the unit cleanly, then you may not be getting the proper pulse to energize the coil. That could happen if the LOCK-IN circuit on the OUTHOLE relay wasn't keeping the OUTHOLE relay energized.

#7 2 years ago
Quoted from sraasch:

Right now, the solenoid pulls when it's supposed to, but not enough to advance the unit. By hand, the mechanicals seem to be ok.

Some other possibilities:

- The plunger may be mushroomed at the end where it slams into the coil stop. Make sure there are no sharp edges there.

- The stepper gear may not be staying put as the advance solenoid fires. What should happen is that the toothed gear is held in place by a ratcheting mechanism to keep it from rotating backwards. When the solenoid fires, the advance lever reaches across a gear tooth to the far side of the tooth and the spring pulls it to the next position when the solenoid relaxes. If the latch holding the gear isn't adjusted properly the gear may be rotating backwards as the advance lever tries to slide over it. When this happens the advance lever doesn't catch the next gear tooth and can't advance the gear.

- The advance lever that grabs the next gear tooth may be worn to the point where it can't reliably grab the gear tooth.

#8 2 years ago
Quoted from MarkG:

Some other possibilities:
- The plunger may be mushroomed at the end where it slams into the coil stop. Make sure there are no sharp edges there.
- The stepper gear may not be staying put as the advance solenoid fires. What should happen is that the toothed gear is held in place by a ratcheting mechanism to keep it from rotating backwards. When the solenoid fires, the advance lever reaches across a gear tooth to the far side of the tooth and the spring pulls it to the next position when the solenoid relaxes. If the latch holding the gear isn't adjusted properly the gear may be rotating backwards as the advance lever tries to slide over it. When this happens the advance lever doesn't catch the next gear tooth and can't advance the gear.
- The advance lever that grabs the next gear tooth may be worn to the point where it can't reliably grab the gear tooth.

The adjustment screw could also be out of alignment causing the stepper arm to not reach far enough to grab the next tooth

#9 2 years ago

Went through getting a Big Deal up and running a few months back and had an issue with the same stepper.

What finally got it 90% of the way there - cleaning it up and lubing the contacts.
The final bit - replacing the ancient metal coil sleeve. Surprising at what a difference it made.

In case anything in there helps out - here's an old thread that I had running while getting the machine going.

Good luck - it's a pretty decent EM in my book. Broke 1,000,000 for the first time recently. Felt pretty good. Double and max that bonus, then chase the extra ball. Seemingly simple, but so challenging at times.

#10 2 years ago

Thanks to everyone for your ideas.

Just for clarity: when the circuit is energized, the coil moves very slightly (there's just a tiny bit of play in the mounting), but doesn't have the power to move the actuator.

I've ruled out an mechanical issues with the stepper. It moves smoothly and I don't see any wear or gumming. I removed both springs and operated the levers by hand to validate this.

I'll keep the idea from dr_nybble about replacing the sleeve in my pocket for the moment. Seems like good advice in general.

I think my next step is to use the technique mentioned by jeffc to work through the circuit. I had tried something similar, but I think I was too haphazard in my approach.

beatnik-filmstar: Can you elaborate on the bit about replacing the metal coil sleeve? Your link to that old thread didn't post.

#11 2 years ago

sounds like you have a problem with a score motor switch either being dirty or not making full contact.on your game the score motor switch that pulses the coil for the player unit is located on the 3rd switch stack furthest from the front of the machine.Wms actually labels it #2 even though it is in the 3rd position.the switch that needs to be adjusted /cleaned is the 2nd from the bottom of that stack.make sure you tighten the 2 screws on the stack before you make any adjustment.next clean the contacts on both switches.finally turn the score motor by hand to make sure the switches are in proper adjustment.as always make sure the power supply is disconnected before you start working on the game.that should do it for you.

#12 2 years ago
Quoted from sraasch:

beatnik-filmstar: Can you elaborate on the bit about replacing the metal coil sleeve? Your link to that old thread didn't post.

My mistake. Forgot to paste it in.
https://pinside.com/pinball/forum/topic/williams-big-deal-1977-score-reels-not-resetting

With regards to the issue that I was having - I had taken the bakelite plate off the stepper, cleaned it up, lubed it, etc. Pulled springs, made sure things werent gummed up and put it back together. Things seemed to work by hand just fine, but the stepped wasn't advancing right. It would go from player 1 to 2 just fine, but then not be strong enough to go from 2 to 3 or 3 to 4. Replacing the 40 year old metal sleeve did the trick.

Quite possibly not related (I'm just some guy that got a single EM up and running a few months ago.) but... you mention that the coil moves slightly, but not enough to move the actuator.

The final issue I had involved a score reel that wasn't working right. The coil for it would move slightly, but not pull in the arm to ratchet the wheel up. Caught the behaviour with some slo mo on my phone.

Turned out to be a switch on the 100 point relay that wasn't clean enough. Wild ass guess, but maybe check the switch that send the signal to the stepper telling it to advance? And as I write that, I see belbs316 saying something similar, as well as telling you where it is. Check that video - if that looks like the behavior you're seeing, I'd bet that belbs316 has pointed you in the right direction.

#13 2 years ago

belbs316 - That was (one of) my first guesses. I've cleaned that switch a number of times, but I didn't check the screws. Thanks for that tip. I think I would have noticed if they were loose.

I'm finding it challenging to get into the switches on the score motor to test and make adjustments. I haven't removed the board from the cabinet, and simply unscrewing the score motor assembly does help, but not as much as I'd like.

I bought a switch adjustment tool, but I'm finding it's still quite hard to get to the back of the switch to make the adjustment (even with the 90-degree end, which is too long to get in next to the adjacent switch). I've been tempted to unscrew that stack to get at the switches, but I'm afraid of creating an even bigger problem. I'd appreciate your thoughts on that.

Overall, the score motor seems to be operating correctly (As far as I can tell, the ONLY thing not working right now is the player advance), having played and visually inspected the operation.

When I've worked on tube radios, the go-to contact/switch cleaning method is to use DeOxit. I can see how that's not quite the best bet here, since it relies on a bit of friction to perform the cleaning operation. Any thoughts on this?

#14 2 years ago

I unscrew the switch stack since, as you have seen, it is hard to get at the switches while they are in place.
There is quite a bit of travel for the switch stack in the score motor so you don't have to be super fussy about the switch gaps.
Personally I clean switches with isopropyl alcohol and use the flexstone file as well.

1 week later
#15 2 years ago

dr_nybble - thanks for the note on the switch travel, that's a good note.

So, I finally got a chance to take another look... Part of my problem was putting a meter on the problem circuit. Finally:
1) Reference from the 6v lamp supply
2) Use an analog meter so that I can watch the needle

I had replaced the wire running from the score motor to the player reset relay (DPDT that drives the player unit step-up or reset coils), but that didn't do it. I was only seeing a small swing on the player unit coils... sometimes they worked sometimes not so much.

It finally occurred to me that what I really needed to do was cut that wire to the player reset relay so that I could watch the score motor switch w/out the coil supply driving that side of the switch.

Sure enough, once I did that, I only saw a small swing (roughly 1V) instead of the 6V that I should have seen... so that switch is clearly the problem.

I've cleaned it and adjusted it, but no joy... The swing on the player reset relay side is 1V, and the other side shows 6V... I've already re-soldered both sides, so I'm guessing it's the contacts... I'm going to have to disassemble the switch (which kind of scares me due to all the pieces-parts) and get my eyeballs on it.

Any last-minute switch disassembly/repair tips?

#16 2 years ago
Quoted from sraasch:

dr_nybble - thanks for the note on the switch travel, that's a good note.
So, I finally got a chance to take another look... Part of my problem was putting a meter on the problem circuit. Finally:
1) Reference from the 6v lamp supply
2) Use an analog meter so that I can watch the needle
I had replaced the wire running from the score motor to the player reset relay (DPDT that drives the player unit step-up or reset coils), but that didn't do it. I was only seeing a small swing on the player unit coils... sometimes they worked sometimes not so much.
It finally occurred to me that what I really needed to do was cut that wire to the player reset relay so that I could watch the score motor switch w/out the coil supply driving that side of the switch.
Sure enough, once I did that, I only saw a small swing (roughly 1V) instead of the 6V that I should have seen... so that switch is clearly the problem.
I've cleaned it and adjusted it, but no joy... The swing on the player reset relay side is 1V, and the other side shows 6V... I've already re-soldered both sides, so I'm guessing it's the contacts... I'm going to have to disassemble the switch (which kind of scares me due to all the pieces-parts) and get my eyeballs on it.
Any last-minute switch disassembly/repair tips?

Unscrew the stack and tape it together so none of the parts fall off the bottom end of the screws.

Best way to clean is with a carbon steel dremel brush but if you don't have access to one a file will work okay.

After taking it off and putting it back on you'll need to double check all the switches in the stack to make sure they're still gapped properly

#17 2 years ago

Thanks. Tape sounds like a good solution here.

FWIW: The schematic piece I was talking about:

player unit trouble (resized).png

#18 2 years ago

Yeah, it's no big deal taking a switch stack out. Just keep everything together & clean contacts with a wire brush in your Dremel. If you don't have a Dremel & wire brush, then get one. NOTHING works better & the brush technique is gentler on the contacts than a file.

4 weeks later
#19 1 year ago

Thanks again everyone for the advice. It's been a busy month, but this thing is back to driving me nuts.

I took the switch stack apart, and it pleasantly only came apart into the individual switches. I've examined the switch, and it seems_ fine.

When I disconnect the motor and turn it by hand, the player unit relays engage just fine. When the motor runs by itself, they (usually) don't.

I cut the wire between the score motor switch and the player reset relay, so that I could better measure the voltage out of the score motor switch. On the "left" side of the switch (see schematic above), the voltage swing on the meter seems fine, on the right side it seems low (again, while the motor is running normally).

I'm thinking the best option would be to replace the switch on the score motor, but I've not found an appropriate-looking part yet (help?). It bugs me that I can't figure out how to clean this switch!

I've replaced the wire running from the score motor to the player-reset relay already, that did nothing.

Has anyone seen these kind of symptoms (score motor switch is fine when run slowly, but doesn't work well at full speed) before?

ARGH!

#20 1 year ago

For completeness sake: I did adjust the switch... I made sure that when it was actuated, there was a bit of movement in the stationary leaf.

thanks!

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