(Topic ID: 28220)

What causes a coil to lock?

By bklossner

9 years ago

Topic Heartbeat

Topic Stats

  • 14 posts
  • 8 Pinsiders participating
  • Latest reply 9 years ago by ChrisHibler
  • Topic is favorited by 1 Pinsider


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#1 9 years ago

Hi folks,

Simple question.

What causes a coil to lock?

On Thursday, my very happy Haunted House table was playing fine. Turned it on Friday night and... "Thunk! Thunk! Thunk! Thunk! Thunk!"

I grabbed my DMM and opened the sucker up. One of the coils went from 2.8-ohms resistance to suddenly 15.8-ohms! Wow.

Ordered a new coil from Marco (actually, a couple of coils just in case) and will replace it when it arrives.

But, I'm just wondering... why do coils lock? Old age? Faulty wiring? Comets? Voodoo priests? Sun spots?

And, yes, ALL of the necessary/mandatory System-80 ground mods were performed a long time ago.

This is just a general question.

Thank ye.



#2 9 years ago

bad transistor on the driver board.


#3 9 years ago

Looks like the coil on the pop bumpers.

Anyway those get pretty hot and heat kills coils.

Do not know how Gottlib specs thier coils but for example Williams uses

Like AL 23-1200. 23 being the wire gauge. Smaller numbers (thicker wire) does not heat up as much but costs more when making higher resistance since you need more turns. The second number is turns on the coil. More turns the weaker the coil.

Pop bumpers should have thicker wire to handle the constant use in the game. Make sure the coil is the correct one for that position in the game and check if there is any service bullitens that may have switched to another coil.

Coils get hot and build up resistance as they get hotter. Older coils can also heat up quicker if they were damaged from heat over the years.

#4 9 years ago

This is definitely a nice start. Thanks a bunch so far!

The coil is for the hole-kicker on the lower-playfield.

I have the schematics, including part numbers, along with a bunch of other System-80 guides and haven't come across a bulletin on this particular coil.

Oh, the driver board is a new Ni-Wumpf board. I'll check that out too just to be sure that isn't acting goofy.

And the fun begins.

#5 9 years ago

Check it cold and then after you play it. If its a slight change then do not worry about it. If it locked up then its another thing.

I usually will put the coil I feel is needed. Like on My HS2 I upped the coil on the kicker.
Same with flippers. I start with what they recommend the change from there.

#6 9 years ago

The resistance actually increased? That's a first. Probably because you were testing it hot? In this case the transistor was good but the switch was stuck closed, so the game kept firing the coil thinking there was a ball there. If the coil had locked on and stayed on, it would be a transistor.

#7 9 years ago
Quoted from Crash:

The resistance actually increased? That's a first.

I was thinking that too.

#8 9 years ago

Actually, I hadn't turned the game on at all when I took that picture. I mean, it had been plugged in but not turned on. The table had been turned off all night.

Verrrrrrry interesting.

Something simple like a short?

I'll remove the lower playfield and inspect the connections if that's the case.

#9 9 years ago

Okay, new approach here folks.

It appears the coil is fine. I tested the resistance of an equal coil on the main playfield and it shows the same value of 15.8-ohms. I guess it's probably a short or something.

Thanks Crash, I thought all of the coils had the same resistance value. I guess not.

Trying another approach. Maybe tomorrow.

#10 9 years ago

Whoa pardner,

Coil resistance can not go up.
That coil is fine.

If the coil was firing over and over again, versus "locked" on, then the game thinks there is a ball in that kickout hole. Examine the switch. It should be gapped at about 1/16".

If the coil is actually locked on, you may, and probably do, have a transistor issue.

Check the easy things first.
Chris Hibler - CARGPB #31
http://www.PinWiki.com - The new place for pinball repair info

#11 9 years ago
Quoted from bklossner:

...I thought all of the coils had the same resistance value. I guess not.

Link below to a coil resistance chart. Not all coils are listed, but most are including your A-16570.


#12 9 years ago

Shorted transistors cause locked on coils

#13 9 years ago

Right. Update:

Everything's fine. The coil's working and was never faulty.

I removed the lower playfield, checked everything out, made sure there weren't any wires touching and re-installed the playfield.

Turned the machine back on and.... no thunks. It's just fine.

I examined the switch to make sure it had the proper clearance. I think that must have been it. Just needed a little jostling to free everything up.

Thanks for the advice everyone. I'm still *very* new to pinball maintenance, mechanics, and electrical engineering overall, so most of the time I really have no idea what I'm talking about.

I guess I know *just* enough to be dangerous and make people think I'm smart. Hah.

So, yeah. Thanks everyone for the pointers.

Maybe next time I'll do some research before immediately going to you guys.

#14 9 years ago

Congrats B.
You know enough to ask for help when you need it. That's a good start!
Enjoy the game.
Chris Hibler - CARGPB #31
http://www.PinWiki.com - The new place for pinball repair info

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