How do know whether a coil is still good or not? how do you test it?

Thanks.
Claude.

http://www.pinballhq.com/fix (Marvin/Clays Guides) ....


http://www.pinrepair.com/sys1/index.htm#coils

From marvin repair tips:

A very good idea for any unknown game just purchased is to check all the coils' resistance. If the game is new to you, and you have not powered it on, a quick check of coil resistance will tell you a lot about your new game. This takes about one minute and can save you hours of repair and diagnosing work.
Any coil that has locked on (usually due to a short solenoid driver board transistor) will heat up and have a lower total resistance. This happens because the painted enamel insulation on the coil's wire burns, causing the windings to short against each other. This will lower the coil's resistance, causing the coil to get even hotter. Within a minute or so the coil becomes a dead short, and usually blows a fuse.

If the solenoid driver board (SDB) transistor is repaired, and the game is powered on with a dead-shorted coil, this will blow the SDB's same transistor again when the coil is fired by the game for the first time! There is no sense making more work for yourself. So take 60 seconds and check all the coils' resistance BEFORE powering the game on for the first time!

In order to check coil resistance, put your DMM on its lowest resistance setting. Then put the DMM's red and black leads on each coil's lugs. A resistance of 2.5 ohms or greater should be seen. Anything less than 2.5 ohms, and the coil and/or driving transistor may be bad. Now remove the wire from one of the lugs of the coil, and test the coil again. If the resistance is still the same (low), the coil or diode is bad (and also perhaps the driving transistor). If the resistance is higher than 2.5 ohms, the coil is good but the solenoid driver board transistor is shorted and will need to be replaced. Lastly, the coil's 1N4004 diode could be shorted too, giving a false low coil resistance. Cut one diode leg from a coil lug and retest the coil's ohms.

When replacing a coil with a new one, and make sure there is a 1N4004 diode installed across the coil's lugs. Remember when reconnecting the wires to the coi that the power wire (usually two wires or thicker wires) goes to the coil's lug with the BANDED side of the diode attached. The thinner wire is the coil's return path to ground via the SDB.

This method requires that you have the boards connected...mine does not have the boards for now (they are out for repair), so it does not test good. Any other ways to test those coils?

Quoted from ALJO

This method requires that you have the boards connected...

Where does it say the boards have to be connected?

Quoted from Monkeybug

Where does it say the boards have to be connected?

Your right, I must of misread something....anyway, my tester reads 0 ohms on any coil????

What's your tester?  Maybe it can't read low ohm value correctly?

This.

Double check to ensure the meter is set to a really low ohm value, otherwise it won't register on that meter.

Also, if it tests open, check the windings of the coil around the lugs for breaks.  (this is usually where the wire breaks off, and you just need to resolder it to the lug)

D

Ah...... when did you last change the battery in your meter?

Your meter only has two scales R X 10 and R X 1000. Try R X 10. It won't move much on there...... after you check the battery.

Go to Canadian Tire and buy this. Do it today:



It's not the best, but I use this model every day and it's good enough for pinball purposes. How have you managed to maintain pinball machines for so long without a digital multimeter?

Make sure its auto ranging.

I've been through at least 4 (because I always cheaped out).  I finally bought a Fluke and never looked back.

Quoted from necro_nemesis

Ah...... when did you last change the battery in your meter?

Your meter only has two scales R X 10 and R X 1000. Try R X 10. It won't move much on there...... after you check the battery.

Changed the battery, but does the same thing, the multimeter's needle goes right up and rests on the stopper when I test the coils.

Quoted from cooke

Go to Canadian Tire and buy this. Do it today:



It's not the best, but I use this model every day and it's good enough for pinball purposes. How have you managed to maintain pinball machines for so long without a digital multimeter?

Like I often said, I am not good for repairing what I can't see is broken on a pinball game and that's why this multimeter was perfect for me.
I'll go buy one when I have time, thanks for the tip.
Claude.

Quoted from Monkeybug

Make sure its auto ranging.

I've been through at least 4 (because I always cheaped out).  I finally bought a Fluke and never looked back.

Well noted.

Thanks.

Quoted from ALJO

Like I often said, I am not good for repairing what I can't see is broken on a pinball game and that's why this multimeter was perfect for me.
I'll go buy one when I have time, thanks for the tip.
Claude.

This meter goes on sale regularly at Canadian Tire for 75% off - so don't rush unless you have to..., but I guess you are in need of one now..

Quoted from ALJO

Changed the battery, but does the same thing, the multimeter's needle goes right up and rests on the stopper when I test the coils.

Not suprising with the range options you have. No offence but that meter you have for this application is a POS. Any modern meter with auto ranging will pretty well suffice. What I would look for is an audible tone continuity feature, auto ranging, range hold and diode testing. Some of the better meters will be able to handle more amperage for testing current, but high current testing is not something that gets used often for diagnosing pins. So don't fork out the money for this capability that you won't require.

I bought this on a 60% sale at Canadian Tire.

Now, I tested my coils and some read 12 ohms, some 14 ohms and some up to 32 ohms, is this normal??

Never mind, I just read clay's guide to pinball repair and I got my answer.
Thanks anyway.
Claude.