You have to cut an end to test it. Just replace it (IN4004). Make sure it's install the right way.

Bad things. Would just replace it if it's suspect, they're really cheap, even if you have to go to Rat Shack or whatever the Canadian equivalent is.

My understanding is the coil, when energized, creates some strong electro-mechanical forces/current. These such forces can backfeed (go the direction they are not wanted to go) through the other polarity and to your main CPU board & transistors. Most times it usually cooks/fries/overheats the transistors in that path and then they need to be replaced (not repaired, must be replaced).

It is best you do not play your game is you have a suspect diode. Just replace it. They are cheap and if you never did it before, after a little reading you will be able to and it feels good too

Won't a bad diode blow a fuse?

Heating up one lug, and pulling it out to test is much faster than replacing it.

just be careful you don't disengage any of the coil winding leads from the terminal - the low power winding is pretty tiny and easy to break

If the diode is shorted, yes. If open, possibly but usually no.

If there is enough lead length, and usually there is, you can cut one lead, measure, then if good re-solder the leads together.

It's very simple to test. First set your DMM on low ohms. Then put each DMM lead on the coil. (i'm assuming a 2 lug coil here, by the way.) Depending on the coil (it would have been nice if you told us the coil number), you should get the resistance of the coil (generally 3 to 300 ohms.)

Now if you get less than 1 ohm, that's basically a dead short. There are two reasons for this - either the coil diode is shorted, or the coil has internally "baked" and is shorted. Now cut one leg of the diode from the coil. Re-measure the resistance. If the resistance changes, you have a bad diode (and probably a good coil.) If the resistance is the same, you have a good diode. (And while you have one diode leg cut from the coil, you can use your DMM's diode test to test the diode - black DMM lead on the banded diode leg, should see .4 to .6 on the meter.)

Now if you're doing this on a flipper coil (3 lugs), the same theory applies. Just remember that a flipper coil is actually two coils in a single package. The "common" coil lug is the one with two winding wires attached. Knowing that, you can measure each side of the flipper coil independently.

This is where things go a stray. "Series" wound flipper coils will have a single diode. "Parallel" wound flipper coils will have 2 diodes. Doesn't really matter, you just have to do the resistance measurement based on the diode(s) position on the flipper coil.

bottom line - less than 1 ohm of resistance, cut the diode off and see if thing change.

I am super pumped to see you are contributing to pinside with you knowledge Clay.

So here's my diode dilemma. I brought home pinbot and noticed a sling not working. I checked it out and a wire was yanked from one of the lugs.. so i resoldered and upon turning on, the coil locked. Sent boards to coin op for repairs thinking transistor.

Should I be concerned with the diode on that coil too?

If the coil locked, this shows it can turn on so it is probably good. You may have a shorted drive transistor causing this lock on condition. The wire may have been yanked due to the coil locking on.

You should check your coil and diode easily enough following the instructions in this thread. This will tell you for sure if your coil and diode are OK or defective.

Not if on the Flipper coil. If the diode is on a switch, yes it can cause a switch matrix problem.

My concern is that I get back my board from Coin op (working 100%) and a bad coil diode on the sling ruins the transistors on the board (after it's been repaired).

Can this happen? Or would a fuse just blow?

Yes it can, and a fuse won't always blow. If the diode is bad, the next 'diode' in the system is your newly fixed transistor, which will bleed off the back EMF, and can destroy the transistor very quickly.

The best thing to do, while you are waiting for the board to get back, is test the diode on the coil in the game, or as others have said, just replace it.

A locked on sling will blow the fuse, that is, if the fuse is rated correctly. Make sure the game isn't overfused. It's the first thing to check when you get a new game imo.

If you're worried about the diode, replace it. Make sure it's installed correctly. Power to the band. Don't always copy what's installed. Also, a shorted sling switch can cause a lock on too. just fyi.

Whenever I test a diode, the meter bounces around from different readings.. some in the 600's.. then boucing up to 900's etc. I have my meter on diode mode too i believe.

Learned my lesson a few years ago. Bought a seeminly fine game, no major problems. Later, looked at a fuse (I don't remember why--nothing was really wrong, I was just checking them, to see what to buy to have on hand). It was the wrong value. Started looking at others in that game...wrong value...wrong value, etc. After completely going through the game, about 70% of the fuses were all wrong. Weird, its like someone went in there an just swapped them all around for no reason.

So I just tested all my coils on my F-14 Tomcat here is what I found:

Lower Flippers are FL11630: right flipper= .6 & 4.5 ohms / Left Flipper= 2.8 & 4.5 ohms

Upper Flippers are FL11722: right flipper= 62.2 & 6.2 ohms / left flipper=.2 & 6.0 ohms

Other coils (bumpers and such) AE 23-800 all at 3.8ohms; O4-0938 14.3 &14.2 ohms; 26-500 13.9 ohms.

So what I see from this and what you posted is that the right lower flipper is bad and the left upper flipper is bad. I guess it could be bad diodes or other things but ultimately something is wrong with each and the easy solution is to just replace them.

Also of note, the capacitors on both the upper flipper coils each have broken conections. What does this do to the effectiveness of the coil and does it have any other adverse effects? I am replacing those either way...

My thought is I will just replace all four flipper coils and start with a known good setup since I am shopping the machine right now anyways! What do you think?

remember when testing wms flipper coils (like f14) for resistance, on older pre-fliptronics games (that use high voltage EOS switch), you need to put a piece of paper between the EOS switch contacts first. Electricity takes the path of least resistance, and the whole purpose of the EOS switch is to short out one winding set in the pair that is a flipper coil. so do that and report back please...

the cap is a spark suppressor. it's not needed but it's nice to have. note only works with parallel wound flipper coils (two diode coils), which your F14 should have.

The paper between the EOS switch contacts solved the problem, the resistance readings are all normal like this. Previously, on a total random but rare basis the the game powers down for a fraction of a second while in game play then goes back to ready to play but ends the game. I heard that a bad coil diode could have this affect so I started investigating the coils. So from what I see it looks like my coils are actually fine and I don't need to replace them. I will replace the capacitors though. Any ideas on what would cause the above described power down (I did a 24 hour burn-in and there were no problems there)?

When testing these coils, the cpu should be connected, correct?

Mine is out of the game right now..

Not necessary for the tests discussed in this thread (i.e. diodes and coils).

There's no reason to have the machine powered on when testing these. I'd strongly recommend against it, unless you are feeling really lucky....

Oh, game would be off either way.

I'm really just trying to make sure that when I place my new $365 high speed cpu into the pin, the coils, etc don't screw something up on it.

SO, i'm trying to learn to test the coils. I'd like to test them now, with the board not in the back yet.

gotcha. Well, this is indeed the perfect time for you to do it.

Is it normal that when I test, the digital multimeter's readings bounce all over the place?

No. Did you see the post from Cliff above?

As a test, just find any 2 lug coil under the playfield, put the leads on either lug, set to ohms, and you should see a rock solid reading >3 ohms.

If you can't get any consistent reading, it might be time to try a new 9v battery in the old MM.

wow. All this time I thought that was normal.. the numbers bouncing around!

My meter was free with a coupon from Harbour Freight.

So I changed out the 9v and retested. All coils seem around 7.9 and above. Some much above. The mm readings fluctuate upon first placing the probes on the lugs of the coil I'm testing .. but generally after a few seconds land on a number.

I think my coils are good.

Would agree. Depending on the type of coil some will read much higher. Now on to the diodes.

Blackbeard, it is also good practice to always put your two leads together especially before testing in diode and resistance mode to ensure your leads are good and and their connection is good...plus it gives you an idea of what your meter will read in reference to a dead short.

Edit: BTW, I find a good practice for testing mounted diodes that are suspect is to use your finger or a screwdriver to pull the diode away from the coil so its not touching anything and then pull just a little harder so it breaks..."oops, guess I gotta change it now".

Do I have to cut all those diodes just to check them though? This seems rather painful. Do people really unsolder (or cut) all the diodes from to trying a game the first time, just to test them?

What happens when a diode goes bad when you have had the game for awhile? Doesn't a fuse blow or a coil lock on to alert you without having to always be testing them?

Yep, if you don't you will read through the coil and not get an accurate reading.

Unfortunately no. Depending on where the diode is mounted (flipper, sling, light, etc) different things will happen. Could lock on, blow trasistor on the board, cause resets and lock ups. The biggest diodes you have to worry about failing are the ones that get the most action...and when I say action I am also talking about vibration. It is not common for light socket diodes to fail (not saying they don't) but the diodes I have found to fail the most would be flipper diodes, pop bumper diodes, and then sling shot diodes. In my ventures I have found that most of the time diodes don't fail they break or come loose...just some food for thought. Hope this helps.

It does help Jw. The more I can learn the better.

The HS was resetting (prior owner told me) and I had found a broken diode on one of the flippers, which I replaced.

Just had unsoldering things to test. As soon as I start to heat up the lugs, the wires come loose, etc. Can be a pita!

Even with all the right tools it can be a PITA! I don't know the technical term but do you have one of those clips for soldering? It is a reverse pair of tweezers that really help. If I am having problems using my third hand I use this clip to keep the wires attached to the coil lugs.

I usually just use an allegator clip to hold things.

I think you're talking about a hemostat.. keeps things clipped.

Honestly, I might just gamble and not undo all the diodes and check them.

I just looked up hemostat and that would probably work but here is a picture of what I am talking about. Honestly I really don't see the need to check all of the diodes. If you are having a problem with a coil or lamp row or column then yes but other than that I don't see the need.

Soldering-Aid-Tools-ProsKit-108-361.jpg

Yep, I have a tutorial on my blog sttng repair if you want a how to with pics

Www.ovfdfireman.com

Nice tutorial OVF.

My question is this though: is it common practice to unsolder (or cut) all diodes on coils to test them when getting a pin for the first time just for the sake of checking them... OR is it more common to wait until there is some sort of issue with the pin before cutting/testing diodes?

Just seems like a bit of a pita to cut/test all diodes everytime you get a new pin. (new meaning used)

I would only test a diode on a particular coil you think is causing trouble. There is no need to check ALL the diodes unless you just want to.

No, don't fix it unless its broke as you are more likely to have issues. Diodes don't usually go bad, and when they do you get a symptom or issue. Like a fuse blowing when a solenoid energizes, or game resets when you hit the flipper. But honestly they just don't go bad too often. So enjoy you game and the only thing I would do regarding diodes is pick up a couple to have just in case.

Good luck

The only game I've bought that was fused correctly was my Iron Man, and it was about 9 months old and from the original owner.

With the exception of a few HUO Sterns that the original owners still had, I've never worked on a game that was entirely fused correctly. The only game that came close was batting 1000 until I got to the main fuse in the cabinet, it was wrong.

After I buy a game and get it home I don't even fire it up again until I've gone through all the fuses.

Very good preventative maintenance!

I change out all the fuses whether they are good or bad...That way I know for a fact it's the correct fuse that's in there.It takes more time to pop out that fuse and check to see if its the correct amp,Just put in new fuse much faster.

I think what you're attempting to describe is a heat sink clip. it's meant to be placed between the area that you're working on and a component that you don't want the heat from the soldering iron to get to. they usually have a good sized block of metal on the ends that clamp down to help dissapate the heat generating by the soldering iron.

http://www.radioshack.com/product/index.jsp?productId=2103242

Hey ovfdfireman, where is this tutorial? I can't seem to find it.

DAMN YOU!!! *Shakes his fist*

I'm reading this thread from the top and starting to think,,, hey wait I minute,,, I remember this this thread,,,,, and then I noticed the date and that you resurrected it!! Damn dirt apes!!!!

homer-simpson-doh-2.jpg