Lincoln Electric LE31MP welder not turning on

[tibimakai]

This is my own welder, that blew up while welding. There is no warranty on it. Purchased it a year ago, sealed box from Craigslist.
It worked great until now, about a year.
What I have found is a blown trace next to the main capacitors, it seems like also got damaged the SMPS IC, output MOSFET and a 1 Ohm resistor to the ground from the MOSFET.
After replacing these components, the relay, fans turn on and it sounds like it's working, but there is no output voltage for the welder, LEDs do not turn on.
So there are more components that are damaged.
I'm having a hard time taking measurements, since there are quite a few transformers and I'm not sure from where to get ground at each stage.
I have never repaired a welder before, only TV/receivers/laptops, etc.
It seems like the low power supply is working, but nothing after that. Or maybe I still have some bad components in the low power supply.
The three capacitors next to the blown MOSFET show there value, did not check ESR though.
Fast diodes on the heatsinks, and IGBTs are not shorted.
I can't find a service manual either.
Any help would be appreciated very much.

Tibor

[CapLeaker]

Re: Lincoln Electric LE31MP welder not turning on

I can tell you this much that everything is o.k. including the main filter caps. This looks more complicated than one of these Chinese cheap welders. However I'd say they are similar if you compare them. This gives you a little idea on how this thing works.
https://danyk.cz/svar.png
https://www.badcaps.net/forum/showth...ghlight=welder
https://www.badcaps.net/forum/showth...ghlight=welder
https://www.youtube.com/watch?v=Mf_dD-Sh1n4&t=10s
https://www.youtube.com/watch?v=MAg7...CYzYYkTtt9dQ0Q

here is a plasma cutter that I had repaired:
https://www.badcaps.net/forum/showth...ghlight=lgk+60

You can read up on these. There are pretty good clues and misleads (so close and yet so far) in there why something wont work. As for now, I got no clue myself on your unit like this. Could be various reasons and one by one this inverter welder has to be checked for certain things.
Good luck on reading up on all this!

[tibimakai]

Re: Lincoln Electric LE31MP welder not turning on

Thanks for all those links, I will have to read those.
I have also found this guy on Youtube, that ahs very nice videos about fixing the cheaper welding machines, but the basics should be the same:
https://www.youtube.com/watch?v=_3D3Enk9ZLs
This is only one video, but he explains separately each module.

[petehall347]

Re: Lincoln Electric LE31MP welder not turning on

d208 dont look happy

[tibimakai]

Re: Lincoln Electric LE31MP welder not turning on

I have seen a few this way. It is not from manufacturing?
I will check it out again, I think that I have checked it out already and it seemed good.
To me, it seems like I'm not getting the voltage across the transformer. Maybe missing oscillation?

[stj]

Re: Lincoln Electric LE31MP welder not turning on

does the relay bypass the inrush NTC's?
if it does - is it working?

[tibimakai]

Re: Lincoln Electric LE31MP welder not turning on

Yes and yes. I have 14V there for the coil.
I believe that is all that is working right now, and powering the three fans also.
I'm not getting the other low voltages, that are powering the "display"(LEDs) and most likely other important sections.

[tibimakai]

Re: Lincoln Electric LE31MP welder not turning on

That diode looks good, it shows 0.7V.
I have found a component(C005) that seems like it was blown off.
It could have been a capacitor there?
U201 next to the black heatsink, is a UN3843BN switching controller.
By the way, the IC that I have changed, is a UN3842BN it's a DC-DC controller.
https://www.digikey.com/en/products/...3842BNG/920377

[tibimakai]

Re: Lincoln Electric LE31MP welder not turning on

Added more info.

[tibimakai]

Re: Lincoln Electric LE31MP welder not turning on

Added more info.

[CapLeaker]

Re: Lincoln Electric LE31MP welder not turning on

That blown trace… one side is rectified mains and where does the other side connect to?

[tibimakai]

Re: Lincoln Electric LE31MP welder not turning on

Here are some pictures to explain where it goes.
I'm not in front of the board, so I'm using the pictures and I'm assuming that it goes to the transformer and the other end to that capacitor, goes through a via. Most likely I should replace that, right?

[CapLeaker]

Re: Lincoln Electric LE31MP welder not turning on

Something drew a tremendous current to blow up the trace. I just wanna see what else is on this trace that may be open, the via o.k. etc. kind of odd where the trace blew. On the bottom of that trace are 3 resistors in a row. Are those o.k.? Is there something wrong with the X2 cap above the relay?

[tibimakai]

Re: Lincoln Electric LE31MP welder not turning on

That capacitor is installed in a way that I can't read the value but it measures 2.22mF, the gray one behind it is a 2.22uF and measures 2.22uF, the other big yellow is 470nF and it measures 2uF-that one is weird.
The three resistors are ok 3x56k. They are going to the pin #7 of the IC, that I have replaced. That same line goes to C007(right lower corner of the IC.
Please check the pictures.
Eventually it ends up at the octo at the bottom of the board, after going through the big(220uF) cap.
Another thing that I have measured that seems a bit off, is one of the big diodes at the bottom D204, one way measures 0.4V and the other way 0.8V. Maybe it is leaky?
The D202(same diode-ER20) measures 0.4V and the other way is 2.2V.
I did not have time to remove and measure properly.

[CapLeaker]

Re: Lincoln Electric LE31MP welder not turning on

any component that does look fishy, take it our or lift a leg and measure again. Then we can look further.

[tibimakai]

Re: Lincoln Electric LE31MP welder not turning on

I have removed both diodes and the 470nF capacitor, and they are OK.

[tibimakai]

Re: Lincoln Electric LE31MP welder not turning on

There is another SMPS PWM power supply next to the one that I have repaired, that is not powering up.
I have measured 0V at each IC pin(UC3843).
Needs more time to figure out from where it's getting power, in the weekend I will trace it out.
There is a resistor that is getting quite hot(~86C).

[CapLeaker]

Re: Lincoln Electric LE31MP welder not turning on

Lucky U! If it’s gets that hot, there is a short. You should have fairly good going then.

[tibimakai]

Re: Lincoln Electric LE31MP welder not turning on

I'm checking with the thermal. I may have to pay more attention to that area, maybe there is another part that is hot, but because this resistor creates so much heat signature, maybe I can't "see" with the Flir the offending part.

[CapLeaker]

Re: Lincoln Electric LE31MP welder not turning on

Use 99% IPA.