Thread: Unimig 250 MIG - fans run but nothing else

Just to finish this thread off, welder is back and working happily.
Fault was the power control board. Roughly $240 plus some freight etc it was just over $300 all up.

Not super happy it needed such a repair with so little use, but good that it was fixed promptly and that parts etc weren't a drama.

Steve

Similar but different...
Came across this little 140A stick welder of the IGBT Inverter type.

Normal symptoms of failure to chooch, let the smoke out with a loud crack under max current for a significant weld run with an oversized rod. I may or may not have been around to see it
It occurred thru a troubleshooting 'torture test' after the user complained of the over heat light being on (not sure what level of performance he was expecting out of a machine that has a 20% duty cycle at 120A).

In any case, it was buggered, so whatever butchery I perform couldn't bugger it any more.

Pics tell 1000 words:


Bridge rectifier on the far LHS shows where the pixies escaped. Pretty obvious smear of the schmoo all over the heatsink. Note the sticker. 'Danger' is my middle name.

Also worth noting, when I pulled it apart, it was also full of gravel. Previous user seemed to think that the welder performs better in the back of a ute full of packing sand. Wrong again, buddy, wrong again.



Case removed, and you can access the board. Pretty basic hand soldered construction, covered in a very tenacious epoxy-like coating on the back and front of the board. Here we can see the back of the rectifier pins, 4 large pins which need to be de-soldered.


With a bit of cussing and some time on the soldering iron, the offending part was removed. You can see the part numbers written on the note, as well as the part that was blown apart at the time of failure. That is the positive output pin of the bridge rectifier as far as I can tell.

Putting the details of the part into google, you usually get a decent idea of what you are looking at.
This component isw a bridge rectifier which basically turns an AC waveform into a waveform of a single polarity. After this electrical operation, the waveform gets chopped to better replicate a true DC output (Please keep in mind my knowledge runs out soon after this point).

In this case, the bridge rectifier is of the D35SB80 type. I think the 'T' at the start of the part refers to tyco, the manufacturer, but I haven't looked into it that far. Might toddle off to Jaycar tomorrow and see if I can confuse them
Failing that, eBay!

D35SB80 Datasheet(PDF) - Leshan Radio Company

Part should cost less than 10 bucks on innitial search.

Originally Posted by steveG

Just to finish this thread off, welder is back and working happily.
Fault was the power control board. Roughly $240 plus some freight etc it was just over $300 all up.

Not super happy it needed such a repair with so little use, but good that it was fixed promptly and that parts etc weren't a drama.

Steve

Do you leave it plugged in when you're not using it? I had a Kemppi welder fritzed by a lighting/power strike, so have you had any bad weather out your way in the last week?

Originally Posted by spudboy

Do you leave it plugged in when you're not using it? I had a Kemppi welder fritzed by a lighting/power strike, so have you had any bad weather out your way in the last week?

Hadn't thought of that.
I usually leave it plugged in if I know I'll be using it next time I make it out to the shed, but otherwise it's unplugged and put away.
Going back a bit now so don't recall whether it was plugged in when it died, but we've had such crap weather here lately there's a good chance there may have been lightening around.

Will get into the habit of unplugging from now on - thanks.

Steve

I did some more digging for the welder I'm looking to repair.

Found this spec sheet:
[ame]http://docs-asia.electrocomponents.com/webdocs/12fc/0900766b812fc1a1.pdf[/ame]

Part # PB3510 should do the trick... about 20 bucks shipped for 5. Australian stock, same day dispatch, free shipping.

Knowing my luck, I'll solder the new rectifier in and then blow something else!

Did you ever manage to repair the UNIMIG ? I"m considering putting a bid on this one .... but if they have a known issue that is difficult ( or expensive ) to repair, I will give it a miss

UNI MIG Welder 260 AMP in VIC | eBay

I'd be up for a torch, even if it does work for starters. I did send a message last night asking if it at least powers up when plugged in .... But I may have left my questions a little late .... or the things dead as a doornail....

seeya,
Shane L.

Originally Posted by DoubleChevron

Did you ever manage to repair the UNIMIG ? I"m considering putting a bid on this one .... but if they have a known issue that is difficult ( or expensive ) to repair, I will give it a miss

UNI MIG Welder 260 AMP in VIC | eBay

I'd be up for a torch, even if it does work for starters. I did send a message last night asking if it at least powers up when plugged in .... But I may have left my questions a little late .... or the things dead as a doornail....

seeya,
Shane L.

That looks to me like the transformer type rather than an inverter type, so the above info is probably irrelevant.

Much less electronicky bits inside to let the smoke out than an inverter, but if the transformer is stuffed probably only scrap value.

Steve