Repairing Mig Welders Part 1

Safety warning: This blog post is for educational purposes only. Do not attempt to repair a mig welding machine unless you are a qualified technician.

This article is not meant to be a comprehensive how to repair a mig welder manual since the process is very involved and needs a large amount of technical knowledge. Hopefully this will help in giving you an idea of the steps that technicians go through to fix your mig welder.

Unplug the MIG welder from the power point.

Make sure that other people are clear of the machine (for safety purposes.)

Ensure that the plug and cable are not damaged, make sure to look for wear and tear, burning and broken plugs.

Open the welding machine cover.

Check for safety issues first these include doing a visual check Visual check: is there any loose wiring or are there any components that are obviously damaged for eg: PCB, contactor, transformer, capacitors, diode bank, chalk, fan, fan motor, wire feed motor, terminals and leads etc.

With a visual check you should see if any of the wiring or components are burnt out or physically damaged
Is the earth lead attached to the body! This is a very important safety issue the chances of electrocuted rise exponentially when anything is ungrounded.


E.G. of A burnt contractor

(Picture of a burnt out contactor, an obvious sign that something is wrong)

After the initial safety test and assessment of components we focus on other parts of the machine that can cause problems. Obviously it is different for each and every case.

In this case we started by checking for any wirefeeder issues

Check if there is any MIG wire that is still in the gun and then check for the gun damage. If there is still MIG wire in the gun make sure to remove it.

Release the wire feeder pressure arm (in the picture it is the black knob on a 45 degree angle.)

Wire Feeder
We then moved onto the electrical side, once again safety is a major issue when repairing machines potentially putting yourself and those around you at significant risk of being electrocuted. This is why only trained technicians should be repairing machine.

To that end we start by looking at the plug and assessing if it is even safe to turn on.

Visually inspect the plug and the lead for any damage.

In the plug make sure the earth, phase and neutral are connected in the correct method.

Visually inspect the lead if its connected to the machine.

Now it’s time to test the lead and the plug – it can be done by few methods such as what can be seen in the picture. Where the active, neutral and earth are tested with a multi meter.

Testing Plug With Multi-Meter

The other method to test the plug and lead is with a high voltage insulation testing meter, as a side note these are the same meters that are used for test and tagging.

If the testing is passed its time to plug the machine to the main plug.

Press the Mig gun switch to activate the contactor.

Check if the contactor is working properly.

While the Mig gun switch is pressed the wire feeder motor should turn properly.

Please check out our video for testing a contactor at:

These steps ensure that the machine passes basic safety test and that the contactor is allowing current to flow to the rest of the machine.

End of Mig welder repair part 1


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