I figured if I wired it backwards that maybe the thing would just fire in reverse, but I'm not sure what's going on. Old coil was feeling a little weak, was original coil 15 years old or so. Ordered a new one from Marco and installed it. Didn't expect any drama but the fuse blew on the power board. 250v 3a. Replaced it and decided to reverse the wiring on the coil (although I don't see that causing a short that would blow a fuse. In my mind it would just cause the coil to work in reverse?) blew the fuse again. Figured I had a bad coil so I pulled it and replaced with original. Blew the fuse. What the cuss?

With the wires off the coil every other coil on the fuse works fine. With either coil wired in they immediately blow the fuse. Any quick ideas on what bonehead thing I did to cause this?

There's just a small header wire and 2 wire harness headed to this could, which I suspect is working fine. I am going to test voltage on that coil wire next but I suspect it too will be fine.

Thanks!

As a side note - I checked voltage on the wires going to this coil and they're at 70+ DCV all the time? Is that normal? Sorry if it's a terrible newbie question but my assumption is that power would be sent to activate this coil whenever it is triggered vs all of the time?

Reading through the manual trying to figure it out...

CactusJack, you are exactly right. Thanks for all of your assistance. I definitely blew transistor Q3 (Stern RCT machine) and the fuse. I replaced the diode though the old one tested fine.

I learned that the high voltage 50v line (yellow and violet in this case) connects to the side of the coil with the 'line' on the diode, and reconnected it. Installed a new transistor on the power board (not fun), new fuse and re-connected the coil only to have it do the exact thing again.

I did not use the exact NTE2987 transistor that the good man at Stern told me to use, as Mouser didn't have them. They gave me an equivalent with all of the same specs. I'm wondering if that's why it didn't work, or if there could be some sort of short in the coil now since this happened?

SO I guess I will order another new coil, since they're not too expensive, and some actual NTE2987s from Marco.

These lessons aren't fun to learn, but I guess I get a little smarter with every one.

Thanks again everyone - you are all spot on with what ended up happening.

Oh - and let me post a picture of why I was confused on the connection... hang a minute

Notice on the replacement coil, the 1 and 2 labels which look like they correspond to the two posts on the coil. The left side (1) says +50vdc. But the sticker is upside down, as the line on the diode is on the right side in this image, so the other post would get the +50. As a newbie learning this stuff, the sticker appeared to diagram out exactly where I should place the hot wire. But we see where that got me!

Not blaming anyone but myself, but at least want you guys to see how the mistake was made. Adam

IMG_4009.JPG

Thank you guys! I am still fighting with this thing. Even wiring it correctly now still blows the transistor. But I'm not getting the proper resistance reading on the coil now, so I'm wondering if the whole incident caused a short somewhere in the coil? It's maddening.

Your explanations really help. As well as the assurance I'm not totally nuts.

Replaced the transistor, new diode and fuse. Blew the transistor again, even though it was definitely connected correctly with the yellow / purple +50VDC connected to the lead shares by the banded side of the diode.

I'm wondering if the transistors I got from mouser are correct. They didn't have the exact brand / part number that stern recommended so they sent and equivalent.

I have the exact transistors and a new coil with diode on order from Marco. Will try again on Wednesday

The center trace on the board for the transistor has lifted and is looking rough. I'm hoping it can be salvaged.

Ok. That makes sense. I guess I couldn't conceptualize a blown coil, as it's just a wrapped wire. I checked the resistance of the coil and it matched the spec.

But that being said, I have both a new coil (with diode) and proper model transistor on the way from Marco. If it doesn't work I might be out $400 for a power board. That'll be a bad day.

Thanks again for the help!

Understood. Let me see if I can find the part number Mouser sold... The receipt is somewhere around here :-/

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This is the part number that matches what is written on the transistors they sold me, although the ones I got are all plastic, without the metal 'blade' on top. Which is annoying as you can't quickly test for a short the way you can on all of the others.

As an FYI, that coil came from Marco Specialties. I've recently gotten a few other parts from them that haven't been correct (with some really weird issues.)

Definitely. Will call them on Monday.

Ok thanks for that input. I believe the transistor to be good when installed but blowing upon first activation of the coil. I'm thinking maybe the coil is bad from the initial transistor blow. I test the diodes before installing and know they are good.

I've ordered the NTE models recommended by the Stern tech, so I'll get one installed along with a new coil and can't imagine why it would not work from there.

I'm worried about the board though. Some of the traces are having a rough time on the board. It doesn't have many solders left on this transister spot. :-/

Yeah I thought about that. I bought some sockets to solder in a smaller transistor slot on the switch matrix for the same reason. Trying to diagnose that nasty issue has caused me to burn through 6 of them. Literally.

Marco customer service has been exceedingly friendly and helpful. They are fixing these labels that are incorrect marked and priority overnighted new transistors and coils to me. So I should have everything today and hopefully get it all soldered up and back in commission.

My Great Lakes Opto seems to have fixed my Opto problem, so I'm ALMOST at a perfect, 100% working machine with some nice mods.

FINALLY. All good. Put the new coil in and it was super weak... then it went into full activation and blew the fuse. I replaced the fuse but it wouldn't work at all. Think it was a bum transistor or shady solder job by me. Replaced the coil transistor on the power board with a new one from Marco, and soldered it more carefully, and the box is working like a champ now! Even sorted out the long broken opto problem, so I have a 100% working machine at long last. And I've learned a LOT in the last month or so - considering when I bought the pin for $400 I had never taken the glass off of one, or knew it had circuit boards behind the translite

Thanks all for the assistance! I owe you a beer or whiskey if you're ever in Dallas.