Wisconsin Pinball

I am in the process of trying to get my Alien Poker ready for MGC. Previously it was having issues with the board not booting (GI comes on, but it doesn't go into attract mode and the diagnostic LEDs on the board come on solid signifying that the board did not boot properly). I moved the machine to work on it more easily and now it boots just fine (probably another issue, but one problem at a time). Now when I start a game it goes through the normal startup sequence, except the drop targets do not reset and the ball does not kick into the shooter lane. I also noticed that the F2 fuse, which controls the solenoids, was blown. Moe and I dug into this last week Thursday with Garrett's help via text (thanks again Garrett) and tracked it down to the solenoid for one of the five drop targets. We disconnected it from the board and the game played just fine, except for the one drop target not working, and the fuse did not blow. The coil also looked suspect since it was missing some of the wrapping, not sure if that means anything. Here is a picture, it is the one in the middle.
I am guessing that the coil is bad an needs to be replaced and I did have a few questions about that:

1. The manual says that the coil is SA3-24-750-DC but SA5-24-750-DC is what is in my machine. Are they the same/interchangeable?
2. Should I just replace the one coil or is it good idea replace all the coils in the drop target bank while you have the part taken out?

Thanks.

I wouldn't worry about the coil wrapping being partially missing unless the cosmetic aspect bothers you or the windings themselves look damaged in some way. The wrapping itself serves no function and can be missing / ripped for lots of different reasons.

I can't find much info on a SA3-24-750-DC coil (shows up on action pinball as an obsolete part that can be replaced by and SA6) but regardless it seems like you are probably fine since it looks like all your other drop targets are working fine and use the same SA5-24-750-DC coil. I didn't look exhaustively but you might not be able to buy the SA3 version even if you wanted to. I also wouldn't replace all the coils unless you have some reason to suspect they could be in bad shape or possibly if getting to this assembly was just a horrible misery. Coils can add up in cost pretty quick and yours look to be in pretty good shape. Cleaning / replacing the sleeves and inspecting the coil terminals isn't a bad idea if it is easy to do while you are working on the assembly.

There is a decent chance the coil itself could be perfectly fine and it is the diode that went bad. You could test for this if you have a DMM. Most coils that I've seen fail that didn't show signs of overheating in the process fail open (usually because the magnet wire broke close to the terminal somewhere, but sometimes inside the coil). That's pretty easy to test for if you want more info on that. If the coil isn't open and you want to check the diode you usually need to unhook one end of the diode from the coil so you can use a DMM's diode test to check it in both directions. If your DMM is a fairly decent one measuring the resistance of the coil and comparing it to another one can help you identify if there is a major short between turns inside the coil (shorted coil will have a much lower resistance).

Thanks for the quick reply. I figured that SA5 might be a replacement for SA3, but wanted to be sure.

I have a Craftsman DMM, not sure how good it is. I did a resistance check on all the coils and they all are about 4 ohms if I am reading this correctly. I'll desolder the diode and check that. Looks like that diode was replaced before, so maybe it is the one that normally goes bad

In looking at the photo it appears that a blob of solder on the diode could be contacting the metal support under the coil. Keep us posted on what you find.

I agree with Jeremy on the blob of solder possibly touching the frame. Definitely check that.

Now....not being familiar with how this particular drop target bank works, I see that the four that are working have a plunger in them, but not the middle one. I assume it's been removed? If not, if you resolved the electronic problem it still might not pop up if there's nothing to push it up. Again, I'm not familiar with this particular drop target bank and maybe it'd work just fine, but that's what it looks like from the picture.

Yeah, I removed the plunger while I was trying to figure out how to remove the coil. I put it back in. Gonna clean up the solder and test the diode tomorrow. Anyone know what diodes these coils use? I scoured the manual and online and could not find a part number.

Noah,

The diode on a coil is there to prevent a high voltage surge from going back to the circuit board. When a coil is energized, it creates a magnetic field which pulls in the plunger. When current flow is stopped, the magnetic field collapses and creates a high voltage. The diode prevents the high voltage from going back to the circuit board. That being said, the coil diode usually doesn't fail and if it does, it rarely causes a fuse to blow. Testing the diode connected to the coil will always test as a short as the coil winding essentially bypass the diode. To properly test the diode, you would need to de-solder one end off the lug and then test it.

If the "solder blob" isn't the problem, I would focus on either the coil having an internal short causing too much current to blow and resulting in a blown fuse or the associated driver transistor on the driver circuit board shorting out. It could be other things, but I would suspect those two items first.

Have you tried taking the wire that drives the coil you're having issues with and soldering it to one of the other coils (de-soldering that coil's wire first (gray/purple wire))? That way, you can test to make sure the electronics driving the coil are working. Small chance you could damage another coil if the transistor is shorted out, but if it is properly fused, probably a low chance of causing damage.

Good luck with the repair.

I have found when dealing with coil issues like this to test the associated transistor first. It can be done on the board by measuring across the legs. I assume all the transistors driving this bank are in the same spot? Just play the sesame st game of one is not like the other.

I have actually found the typical root cause is a partially broken diode leg. This allows the transistor to blow. That can then lead to a locked on coil, which can then blow the fuse. This makes for a tough thing to diagnose as you may chase your tail. Just my experience but check the transistors.

I actually bet the real root is a flakey coil as it appears there is some physical damage. Shorted coil could also have blown a transistor. Trial and error is your friend and you will figure it out

Thank you everyone for your help with this. We tested the transistors with a DMM and the ones for the bad coil seemed to match the rest of the solenoid transistors, except the ones for one of the other drop targets kept reading open circuit which confused us. It might be nothing since it was tough trying to get the probes in position on some of the transistors with the board still in the backbox. We tried hooking up a known, good coil to see if that caused the fuse to blow and it did. Hopefully I didn't destroy that coil in the process. After we were out of fuses, we decided to call it a night and I ordered a few coils from Marco and a bunch of fuses, transistors, and diodes from Great Plains Electronics so we can take on this problem full force next week.

Good update, you'll get it fixed in no time.

NoahK wrote:Thank you everyone for your help with this. We tested the transistors with a DMM and the ones for the bad coil seemed to match the rest of the solenoid transistors, except the ones for one of the other drop targets kept reading open circuit which confused us. It might be nothing since it was tough trying to get the probes in position on some of the transistors with the board still in the backbox. We tried hooking up a known, good coil to see if that caused the fuse to blow and it did. Hopefully I didn't destroy that coil in the process. After we were out of fuses, we decided to call it a night and I ordered a few coils from Marco and a bunch of fuses, transistors, and diodes from Great Plains Electronics so we can take on this problem full force next week.

pullt the board so you can test easier with it out of the game. Also be sure you test all combinations of red/balck on the legs. I never remember which is the right set of legs to test across but process of elimination will tell you.

Very unlikely that you damaged any other coils as they are tough and would need to lock on an fry for a long time. I am still guessing a bad diode that blew a transistor. That then allows the coil to lock on. Locked on coil blows fuse (yeah fuse for doing its job). Feel free to bring the board to Schwoeglers on Sat and I wil bring my gear. We can get a few more minds looking at it and see what we can figure out/ eliminate. LEt me know if you are going to do this so I can for sure come over.

Hilton wrote: pullt the board so you can test easier with it out of the game. Also be sure you test all combinations of red/balck on the legs. I never remember which is the right set of legs to test across but process of elimination will tell you.

Very unlikely that you damaged any other coils as they are tough and would need to lock on an fry for a long time. I am still guessing a bad diode that blew a transistor. That then allows the coil to lock on. Locked on coil blows fuse (yeah fuse for doing its job). Feel free to bring the board to Schwoeglers on Sat and I wil bring my gear. We can get a few more minds looking at it and see what we can figure out/ eliminate. LEt me know if you are going to do this so I can for sure come over.

I got the driver board out and will bring it to Schwoegler's tomorrow. I'll also bring the schematics in case those are needed.

cool

what are the transistors on this? I or Sean may have some and can bring along.

I will bring my gear, including hakko, so if we need to do some board work we can do so.

The transistors are TIP122 and 2N4401 according to the manual. Several of the TIP122 have been replaced with TIP102.

If I remember correctly, the TIP 102 is more robust than the TIP 122 and is fine for a replacement. Testing transistors "in circuit" with a DMM is about 95% accurate, but once in awhile will give false readings. Since you already have the driver board out of the game, I would replace it regardless. You may also want to replace the 40 pin female through connector on the driver board too. At a minimum, reflow the header pins at the connectors.