Unimig 250 MIG - fans run but nothing else

[steveG]

Went to put the finishing touches on my shed heater this morning - turned on the power switch to the welder, fans run, but nothing on the display :(
Its an inverter model - was working perfectly last weekend.

Gave it a quick look over for a tripped circuit breaker etc but nothing obvious.

Jumped online, downloaded the operators manual for it and go to the troubleshooting section:
"Only qualified technicians are authorised to repair blah blah"
Fair enough - but not even a "make sure power is turned on" type of dumbass tip, or "if fans run but no display your main board is fried"???

Anyone perhaps had the same or similar issue with a Unimig before I send it off for repair?


Steve

[Toxic_Avenger]

Ahhhh Unimig.

Is it still under warranty?

The inverter units often have a fuse on the main board. But opening her up could make you liable for any repairs if it's still warranted.

Might be best to hold out to monday and call their warranty hotline. Might be a simple fix

[Blknight.aus]

yes, there is an over heat control, its a basic thermo switch that shuts down everything and flicks on the fan.

find this and check its continutity.

[steveG]

Thanks guys. Had it close on 4 years now so pretty sure its out of warranty.

I'll fire up the stick welder and finish off the heater today then take a quick look. If nothing obvious will give them a call on Monday.

Steve

[steveG]

110352

Nothing obviously smoked and there's voltage through the main rectifier board to the control boards.
Only thing like a temp switch is the small white component on the main heatsink in photo. Has KWC-075c printed on it. Resistance is 70ohms at about 10deg ambient.

Looks like a call to their support line on Monday :(

Heater works well though :)

110353

Steve

[Blknight.aus]

Trace the wires back from the fan to its control. While I dont have the book for the 250 the break down diagram for my welder (not a unimig but built similar) has a relay hookd up to a thermocouple.

if its not in over heat fan control is done by the control board (it turns on when you strike an arc/pull the trigger and runs for 2 minutes after) or if the thermo couple is over heated it pulls power from the control board and the relay which turns on the fan via a single relay.

[steveG]

Will double check, but pretty sure these fans run straight off the 240v input. They have always run continuously whenever the main power switch on the welder is on.

Steve

[Chops]

Had a problem with ours at work, ended up being just loose/worn connector's. Pulled them all apart, cleaned them up and it all works better than ever now.
I suspect things were not done up tight enough in the first place, and so moving it around to do jobs, connector's became even looser and thus stopped working.

[steveG]

Will check that out. All screw connectors seem to have sealant stuff to stop them undoing.

Steve

[steveG]

Everything seems tight, and gave all the plug in connectors a wriggle just in case. No change so will call them tomorrow.

For the benefit of anyone electrically inexperienced reading this down the track, there's a decent bank of capacitors inside the welder, and it was still holding ~300VDC after being disconnected from mains power overnight.
Its definitely not safe to just disconnect the power cord, pull the covers off and start grabbing wires.

Steve

[steveG]

Quick update.
After a couple of phone calls, ended up taking it in to local repair agent in Geelong who does unimig gear. Didn't realise that they only do basic troubleshooting and send anything tricky back to Unimig in Craigieburn (could have taken it directly there myself).
That's where it is now after the local guys isolated it to a main board issue.

Steve

[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

[Toxic_Avenger]

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 :whistling:
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:

http://www.aulro.com/afvb/attachment.php?attachmentid=111717&stc=1&d=1469190964
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. :cool:

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.


http://www.aulro.com/afvb/attachment.php?attachmentid=111718&stc=1&d=1469190964
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.

http://www.aulro.com/afvb/attachment.php?attachmentid=111719&stc=1&d=1469190964
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 :twisted:
Failing that, eBay!

D35SB80 Datasheet(PDF) - Leshan Radio Company (http://www.alldatasheet.com/datasheet-pdf/pdf/507926/LRC/D35SB80.html)

Part should cost less than 10 bucks on innitial search.

[spudboy]

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?

[steveG]

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

[Toxic_Avenger]

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

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

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!

[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 (http://www.ebay.com.au/itm/131896252073?_trksid=p2050601.m570.l5999&_trkparms=gh1g%3DI131896252073.N36.S1.R1.TR4)

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.

[steveG]

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 (http://www.ebay.com.au/itm/131896252073?_trksid=p2050601.m570.l5999&_trkparms=gh1g%3DI131896252073.N36.S1.R1.TR4)

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

[DoubleChevron]

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

I'm thinking the transformer should be fine. They should all have thermister protection to prevent overheating :confused: I really needed to spot it a few days ago so I could go and have a look. The sniff test will give away a burnt out transformer :)

seeya
Shane L.