Cheap MIG - repairable or landfill?

**mawhins** · 18th August 2015, 10:30 AM

Hi all,

I know I shouldn't have but I bought a cheap MIG welder second hand then proceeded to exceed the duty cycle and burned out one of the components on the board that runs the wire feed.

I've made a few enquiries and have been told it's not economically viable to repair but surely there's a way to get this thing fixed rather than pitching it. I can see what's happened, the part has overheated and the solder has let go. I re-soldered it and got it working only for it to re-heat, which might point to an additional problem I suppose. It works fine other than this, seems a real shame.

My other welder is Arc/Tig of which I only use the Arc because I'm not paying for gas and it's pretty hard to weld the thinner stuff which is a lot of of what I want to do around the workshop/house.

Has anyone else found a way to keep these things running? Am I wasting my time?

**DocBug** · 18th August 2015, 01:01 PM

Strange request, can you post a pic of the pcb and the comp you re soldered, may be able to help out or at least point you in a direction that may help

Regards
Alan

**mawhins** · 18th August 2015, 05:29 PM

Sure, I thought I had some on my phone but couldn't find them. Will take some more tonight.

**mawhins** · 18th August 2015, 05:39 PM

Found the photos,

Its the large white ceramic resister (i think) marked 10W4RJ7. You can see that the fuse cover next this component has also melted.

WP_20140328_001.jpg WP_20140328_002.jpg WP_20140328_004.jpg WP_20140328_005.jpg

**DocBug** · 18th August 2015, 05:56 PM

You can replace the resistor and space the legs off the board with ceramic beads. This will allow more air flow and hopefully cooler running. Another option is to replace it with a aluminium style resistor mounted metal panel to the side and wire it in. Something is drawing more current to make it run hot, but it may be a cheapie design that just runs hot.

This is the type of resistor I am referring to is

http://au.rs-online.com/web/p/panel-...stors/0157544/ . The resistors are under $5 and the freight say $15 max

Small expense for a possible fix I recon....

If you need an account to purchase from them, I'm happy to order and ship direct to you, think it may be freight free too

Regards
Alan

**mawhins** · 18th August 2015, 06:28 PM

Thanks so much for the advice Alan and for your offer to help with buying. Is the one you linked to the right spec? 4.7ohm and 25 watt? Do you think it necessary to hook it up to a heat sink?

**DocBug** · 18th August 2015, 06:42 PM

The one on the pcb looks to be 4R7 @ 10W , the replacement wont be a problem. Note sure what the smallest aluminium version is. Physically it will probably be very close to the size of the one you have. I recon you can bolt it directly to the metal casing to the side of the pcb. Just try be get rid of any insulation so it contacts the steel flat for better heat transfer . If you want to put in a piece of flat ally with some heat transfer paste, it will make it dissipate better.

**jhovel** · 18th August 2015, 08:33 PM

That looks the same as the oard in my MIG welder.
That resistor doesn;t get very hot on my board. So as Alan said, something is causing it to overheat.
My best guess is the feed motor. I was horrified to see the tiny and VERY cheap motor in mine. Straight from a cheap electric toy - you wouldn;t even bother using it in a RC car... I'm just waiting for that to burn out....
Take the feed mechasim out and have a good look at the motor. There might evven be somethjing mechanical loading it over capacitor (friction). You should be able to buy a new one for just a few dollars. I'd replace it for a start. Your resistor doesn't look overheated at all. You might be ale to move it away from the OPCB as already suggested, but I suspect that a replacement motor will leave it just warm anyway.

**DocBug** · 19th August 2015, 12:55 PM

If you are able to run the motor and measure the voltage across the resistor. It will give you an indication of the current being drawn by the feed motor and you will also get an indication on the power being dissipated as heat from that resistor. As another quick test, remove the wire being fed and see if it still gets hot. If not, then check your liner and tips to see if they are binding on the wire. It may be the feed had a tight bearing of the motor may be an issue. If you want to try match it up with a feed unit and replace it. Most that I have seen run 12 or 24V, there may be others, but just an idea. Not sure what type you have in there currently.

http://www.bobthewelder.com.au/produ...13&cat=&page=3

Alan

**Vernonv** · 19th August 2015, 02:28 PM

Originally Posted by DocBug

http://www.bobthewelder.com.au/produ...13&cat=&page=3

The motors in those things are tiny. I have a couple of older MIGs and the motors in them look more like windscreen wiper motors.

**mawhins** · 19th August 2015, 02:49 PM

Will try those troubleshooting tips, thanks all. I'll let you know how I get on.

**mawhins** · 19th August 2015, 02:59 PM

I might just go ahead and order one of these as well. The area next to the existing resistor has definitely suffered heat damage. The fuse cover melted. So I like the idea of panel mounting the resistor. Do you think the one in the link is a match?

**DocBug** · 19th August 2015, 03:18 PM

Nope the value as I see it is 4R7 = 4.7Ohm,

The one you pasted is 4K7 = 4700Ohm

Regards
Alan

**Vernonv** · 19th August 2015, 03:53 PM

As Alan said, you have linked to the wrong value. Try this one - http://au.rs-online.com/web/p/panel-...stors/0158323/

**mawhins** · 19th August 2015, 04:25 PM

Great thanks. So you think the 50W is ok to replace the 10W.

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