(Topic ID: 16948)

Coils Burning Up

By PinballGiant

9 years ago

Topic Stats

  • 8 posts
  • 4 Pinsiders participating
  • Latest reply 9 years ago by PinballGiant
  • Topic is favorited by 2 Pinsiders


Linked Games

#1 9 years ago

A coil on my Jokerz machine recently burnt up and smoked everywhere. Looking further inside the machine I see another burnt up coil that has been disconnected. Does anyone know what causes coils to burn up like this? Is it strange that multiple coils are burning up? Will simply popping a new one in fix the issue or does the problem lie somewhere on the board like a transistor? Thanks!

#2 9 years ago

Most likely a locked on transistor. Find the transistor on the board and do a quick check to see if it is shorted. I do this on all games I purchase. With the power off, meter on continuity, put one lead on a good ground and the other lead on the metal tab of the transistor. If it shows continuity, it's bad. Check them all.

2 weeks later
#3 9 years ago

Okay I finally got around to checking the transistors. I tested all of them and they all tested fine...

#4 9 years ago

Make sure the coils have diodes on them. And some times you can have a bad transitor even tho everything come up fine with the meter. Kinda just had the same problem on my HS

#5 9 years ago

Okay I just looked and not one of the coils in the Jokerz has a diode on it. Was it made this way or did someone really replace every coil incorrectly? Thanks!

#6 9 years ago

Jokerz is a system 11B game....After Big Guns (an earlier 11B), WMS moved the coil diodes to the auxiliary board. So, it's no worry that your coil doesn't have a diode...Unless it is a flipper coil.

The quick and dirty test of testing continuity between the metal tab of the driver transistor and ground with power off usually reveals a locked on shorted transistor but not always. I would use Clay's guides and test the driver transistor, the pre-driver transistor and the diode on the board. One of those is likely fried. When a coil goes bad, it either opens up (no resistance), or shorts (zero resistance). Opened up it just doesn't fire. Short, it's going to blow the fuse. A coil isn't going to burn up unless it's being held on by a faulty driver circuit, so that's where I'd be looking.

I would replace both damaged coils, and briefly turn the game on to see if they are both still locked on. If so, shut the game off and start testing/replacing the transistors and diodes on the board.

#7 9 years ago

I would add that if the game was my own, I'd replace the coil transistors and driver transistors anyway. Sometimes they test good, but act flaky.

After transistor replacement, test before installing new coils.

Clay's repair guide, if you don't already have it:


#8 9 years ago

Thanks guys. I'm replacing the relay because I did it incorrectly before and clay's guide says that makes many coils stop working like I have.

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