What does it mean when pinball machine says bad coil?

[roberts123]

I do not know a lot about pinball machines, so any help at all would help out.

I have a Monday Night Football pinball machine. When i turn it on it says that "Bad  Coil" and I have no clue what it means or how to fix it. So if anybody could help me out I would be very thankful.

Thank You

[shardian]

The game will try to fire a coil so many times before it realizes something is wrong. It then creates an operator report for when the game is turned on the next time.

So...it means one of your coils is malfunctioning.

[Jeff AMN]

It doesn't always mean that something is wrong with the coil, however. For example, on my LOTR I've had issues with the sword ramp coil not releasing balls for multiball and I've had the bad coil report. All I had to do to fix it was tighten up the whole assembly and it performed perfectly afterwards. When it gives you that bad coil warning, it could be anything from the coil itself failing to anything in the entire assembly. Basically the game is saying that the coil has been sent the signal by the CPU to activate but that the desired result hasn't occurred.

Coils very, very, rarely go bad. You're probably looking at something related to that coil, but not the coil itself.

What issues have you seen with your game that would cause it to give you that error?

[ChadTower]

Coils very, very, rarely go bad.

Sure they do.  Frequently.  They don't go bad own their own but they fry themselves all the time if they get locked on. 

[Jeff AMN]

Coils very, very, rarely go bad.

Sure they do.  Frequently.  They don't go bad own their own but they fry themselves all the time if they get locked on. 

Well sure, but that's not a coil issue as much as something else. It's just like a bulb dome will melt if the bulb stays on constantly as well.

[ChadTower]

Well sure, but that's not a coil issue as much as something else. It's just like a bulb dome will melt if the bulb stays on constantly as well.

The same as a flat tire being a nail issue?     It's still a dead tire.

[Jeff AMN]

Right, but what I'm getting at is that you don't just replace coils and call it a day. Something causes the coil to fail, it's almost never the actual cause of issues itself.

[ChadTower]

Agreed.   

[Kevin Mullins]

Is there a test menu of sorts on that particular game that will fire the coils independently or in a sequence to narrow down which coil/circuit to investigate ? (haven't browsed a manual yet)

[briguy]

You can test all the coils with a DMM to really see if its a bad coil. I wouldnt run the machine for long periods of time without testing the coils. A locked on coil can do more damage than good, like cook your driver or cpu board parts.

[ChadTower]

You can test all the coils with a DMM to really see if its a bad coil.

How is that?  The only way I have come up with is resistance vs a known good coil but there is very little info out there on just how far off a coil can be without being a problem.

[shardian]

You can test all the coils with a DMM to really see if its a bad coil.

How is that?  The only way I have come up with is resistance vs a known good coil but there is very little info out there on just how far off a coil can be without being a problem.

A locked coil is easy to test - just wrap your hand around it. You'll be remembering that locked coil for a looooonnnnng time.
I was under the impression that the resistance test and voltage lug tests were to check for breaks in the windings - IE, weak coils. 

[ChadTower]

Breaks or shorts.  You'll either get very little resistance or it'll be open.

That's only a BAD bad coil and you can tell that by looking at it - it's either locked on or the sleeve looks like velveeta.  Don't need a DMM for that.  I'm thinking about coils that are going bad since I generally work on games that need a thorough cleaning/shop.  Not many spot repairs for me anymore.

roberts123, is a coil actually locked, or has the software simply reported a bad coil?