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(Topic ID: 7191)

How does one test a coil?


By Blackbeard

8 years ago



Topic Stats

  • 13 posts
  • 7 Pinsiders participating
  • Latest reply 1 year ago by RaoulJuke
  • Topic is favorited by 9 Pinsiders

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#1 8 years ago

1. Power to machine on or off?
2. What do I set my mm to, specifically?
3. WHere do I place the red/black probes? I see there are 3 lugs on each coil.

THanks in advance guys!

#2 8 years ago

If it's not working at all you can manually activate the coil by grounding the control pin on the boards to make it fire to determine if it's a wiring issue. I'd do some research before grounding anything out but it's not hard, don't have time to look it up right now though but I've done it before on a coil I thought was bad turned out to be wiring issue. Coils don't go bad often.

Off to run a 5k. Have a great morning!

#3 8 years ago

Hmm..pretty sure they work. All boards are out on repair. I wanna test all coils prior to reinstalling boards but not sure how.

#4 8 years ago

To physically check a coil with power off and disconnected from the chain, you would be checking resistance. If it is infinite or really high then the coil is bad, I think it should have like 8-12 ohms if I remember correctly.

#5 8 years ago
Quoted from Pin_Crazed:

I think it should have like 8-12 ohms

I think its 3-4 ohms but I may be way off on that one. I can't remember exactly either.

#6 8 years ago

Yea I agree, it should not be over like 10-12 I think, low is fine. Check the guides to be sure but really you are looking for high resistance.

#7 8 years ago
Quoted from pintastic:

I think its 3-4 ohms

As a minimum, that's correct.

Power off.
MM set to measure resistance (ohms), so set your meter accordingly.
Put the black on one outside lug, the red on the other.
Doesn't matter which color on which lug, mix and match all you want. Put one on the center lug if you want and measure that. Doesn't matter. There is no way to damage your coil or your machine or yourself by doing this. (power off, remember?).
You are looking for a minimum of 3 ohms. If you can't get that reading consistently across the lugs, the coil is probably dead. It might be much much higher , even 25+ depending on the type of coil and it's use. Doesn't mean one is better than the other. It's just the way that particular coil is built. Just look for a minimum of 3 ohms.

If the power is off to the machine - unplugged - you can pretty much poke your MM around anywhere under the playfield and search for readings like this on coils and diodes, etc. You can't hurt anything even if you put your probes in totally illogical places. So no fear.

#8 8 years ago

Thanks examiner. That's the direction i needed. Like the idiot's guide to pinball.

7 years later
#9 1 year ago

Can this test with the Ohms be done with the coil not installed? Ie it removed from the machine and the red & black leads on each lug, set to ohms?

Would this test work? Ive got a bucked of old coils and not sure which are good are bad

#10 1 year ago

Yes. you're better off testing while the coil is off the machine. That way you have it completely isolated.

#11 1 year ago

removed - wrong thread!

2 weeks later
#12 1 year ago

Just a question, i am testing a Gottlieb A-25959 and not sure on the reading i am getting.

with the base upside down so that i am looking directly at the back of the lugs, i am getting the below results with the "x" representing which connection is on each lug

x.......x
[] [] [] = .201 Mohm

x..x
[] [] [] = .197 Mohm

....x..x
[] [] [] = 3.9 Mohm

Based on this is the coil dead? Confused as getting different readings pending which lug i have the lead on. The coil is completely disconnected from the machine.

#13 1 year ago
Quoted from RaoulJuke:

Just a question, i am testing a Gottlieb A-25959 and not sure on the reading i am getting.
with the base upside down so that i am looking directly at the back of the lugs, i am getting the below results with the "x" representing which connection is on each lug
x .... x
[] [] [] = .201 Mohm
x...x
[] [] [] = .197 Mohm
....x..x
[] [] [] = 3.9 Mohm
Based on this is the coil dead? Confused as getting different readings pending which lug i have the lead on. The coil is completely disconnected from the machine.

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