an OT repair question

vintagegamer

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I have a Lincoln MIG welder that worked great until we had a power surge go through our entire house in 2008. I think I bought the welder around 2000 or 2001. It powers up but when you squeeze the trigger to actually weld, nothing happens. At the time I researched it and found out that it was most likely due to a diode getting fried on the circuit board inside......

I got the insurance money for the welder but we needed to use it for something else unfortunately (I was unemployed when it happened). Learning now about to replace components on circuit boards through the arcade hobby, I'm wondering if anyone here might be up for helping me repair this welder? It was $600 new, and I really enjoy using it and I'm used to that model. It's the SP125.

If anyone thinks they might be able to lend a hand, please let me know. If I can get the circuit board out of it to ship I will gladly do so. The manual for the machine can be found below:

http://content.lincolnelectric.com/pdfs/products/navigator/im/IM536.pdf

I would hate to throw this thing out if all it needed was a diode replaced or something.

Thanks!
 
I would treat it just like an arcade machine that needs repair... get the board out of it and start checking for damaged components. I don't imagine there will be a lot of logic circuits, should be pretty straight forward stuff there. Well worth saving if you can.
 
Definately try to fix that thing.

I took a quick look at the manual / schematic from your link and noticed that it has one of those manual reset type breakers that controls the wire reel / weld output. Those things fail and I would start there.

I had a somewhat similar problem with my forklift charger we had a spike and the thing would not produce an output. The stupid resetable circuit breaker was junk (did not indicate a trip) replaced that and has worked ever since.
 
Definately try to fix that thing.

I took a quick look at the manual / schematic from your link and noticed that it has one of those manual reset type breakers that controls the wire reel / weld output. Those things fail and I would start there.

I had a somewhat similar problem with my forklift charger we had a spike and the thing would not produce an output. The stupid resetable circuit breaker was junk (did not indicate a trip) replaced that and has worked ever since.

Thank you I will check that out. I love that welder!!
 
I would say there is something simple in the circuit that the trigger switch is connected to. I used to be a production welder and hated those newer pulsed dc machines (most 110 machines are). Give me an older constant source dc welder anyday. (usually 3 phase)
 
I would say there is something simple in the circuit that the trigger switch is connected to. I used to be a production welder and hated those newer pulsed dc machines (most 110 machines are). Give me an older constant source dc welder anyday. (usually 3 phase)


I actually bought this one because I needed one to learn how to weld so I could put my '66 Chevelle back together. It needed quarter panels, driver and pass floor, and trunk replaced. My neighbor is a pipefitter and welder and recommended this one as perfect for a beginner.

It did the job (both fixing the car and teaching me as well). It worked great until this blasted power surge came through our house. I was so pissed because up until about a week prior to the surge, it had been unplugged and neatly stored in my garage.. If it had been there it would still be working today. :(
 
I opened this thing up last night and took pics if anyone wants to see them. It's got a small circuit board in the top that controls everything.
 
Pics Please!

I am surprised the circuit board is not conformally coated. Most commercial welders have the circuit card dipped in something to protect them from vaporised metal deposits that will kill it.
From the manual it appears that the rectifier diodes are seperate from the board. You should be able to check them with a meter, just like a regular diode but the forward voltage will be higher. You might check them and the temp switch, the circuit breaker, and the windings of the transformer before you get into the board.

Kenneth
 
Pics Please!

I am surprised the circuit board is not conformally coated. Most commercial welders have the circuit card dipped in something to protect them from vaporised metal deposits that will kill it.
From the manual it appears that the rectifier diodes are seperate from the board. You should be able to check them with a meter, just like a regular diode but the forward voltage will be higher. You might check them and the temp switch, the circuit breaker, and the windings of the transformer before you get into the board.

Kenneth

Thanks Kenneth for the info, and yes the board has some ectoplasmic slime on it, thanks for helping me identify why it's there!

Do I need to have it powered on to check the diodes? I checked a few on the board last night and they were all showing "1" (infinity) regardless of whether I had the negative on the cathode and the positive on the anode or not.
 
Here are the pics.
 

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Do I need to have it powered on to check the diodes? I checked a few on the board last night and they were all showing "1" (infinity) regardless of whether I had the negative on the cathode and the positive on the anode or not.


You should have the power off to test the diodes. If they are showing an open in both directions then they need to be replaced.
 
You should have the power off to test the diodes. If they are showing an open in both directions then they need to be replaced.


Thank you sir, I know I found at least one, if not 2 that were like that on the circuit board.

I've circled them on the attached pic.
 

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Just make sure you are getting a good connection on the diodes, the coating may get in the way of taking a good reading. Also diodes, and most components on a circuit board, should be removed from the circuit prior to testing to ensure you are getting a reading of this component only. Usually techs will desolder one leg and pull it from the board prior to testing.
 
Just make sure you are getting a good connection on the diodes, the coating may get in the way of taking a good reading. Also diodes, and most components on a circuit board, should be removed from the circuit prior to testing to ensure you are getting a reading of this component only. Usually techs will desolder one leg and pull it from the board prior to testing.

Arrrrrrrrrrrrrrrrghhhh!!! Rich, please just get on your Cessna and fly over here. I'll buy you dinner.
 
id pop that thing off and check the beckside for popped traces. if you find any replace the component in line on that trace ans see what you get.
 
Does that welder have a circuit breaker in it? I'll have to remember to check mine tonight. Maybe the surge blew out the circuit breaker. I recently lost the circuit breaker on a Golden Tee power supply. A surge took out the breaker internally so it could not be reset. From the outside it looked perfect.
 
Does that welder have a circuit breaker in it? I'll have to remember to check mine tonight. Maybe the surge blew out the circuit breaker. I recently lost the circuit breaker on a Golden Tee power supply. A surge took out the breaker internally so it could not be reset. From the outside it looked perfect.

It does have one, I've circled it in the below image (you can see the back, it has 2 prongs). How do I test if it's bad without causing further damage? It has a button on the front side that when you push doesn't really feel like it has any spring to it. I'd love to find out that was the problem.
 

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