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]

ImageUploadedByTapatalk1466252085.723705.jpg

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

ImageUploadedByTapatalk1466252574.237819.jpg

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