One of my frequent customers brought this machine to my shop and explained the problem.  I powered up the machine and sure enough, white smoke came out. Right away, I unplugged it and got it ready for repair. It was very clear from this demonstration, that plastic is burning, not something serious. The serious thing that I noticed was, there was no fan running and the power switch was no clicking the way it should be.

Some screws were off and the inside of the machine was exposed. The moment I took the cover off, I could still smell the burning plastic.

I head directly to the power key first; because the click on that switch did not sound ok.

Look what I found. I pulled the cable attached to that pin and the pin came out with it. This was the source of that white smoke that we have seen and smelled before.

As you can see, that is the new power switch that was replaced on this machine. This time there was no smoke but the problem of the fan remained. I could not hear the fan spinning.

Total of 6 screws off and the fan was free from the body of the welding machine.

I applied 220 volts to the fan and the fan did not spin which is a sure indication of a bad fan. Now, the reason I said it was a serious issue with this machine because the fan is suppose to cool the machine down when in operation but the problem is when the machine is under a working load, the Mosfets and diodes are heating up and if there was nothing to cool them down, most of them if not all will be shorted and had to be replaced.

In my case here, the customer was so lucky that none of the Mosfets or the diodes were shorted out.

This fan can be taken apart and checked. Sometime it is just a loose wire but in this case, when I opened it, there was no reading on its coil and therefore, it has to be replaced.

This is the coil found shorted inside the machine. I had to replace the whole fan to make it run again. Sometime I find a coil replacement and replace only the coil. As mentioned before this fan runs on 220 AC volts. Sometimes there are fans inside the welding machines that run only on 24 volt DC.

After replacing the fan, it was time to test the machine and check working voltages on it.

As you can see, the machine is on and the fan was spinning freely and nicely. You can also see the new power button that I replace and the power green light is on. Now, if the red light was on I will be concerned because that is a temperature warning light. The machine will not work when that light is on.

This reading is coming from the red and black terminals on that machine. As you can see, the voltage is out and staple. Of course I did the welding test on it and it worked perfectly. Mission Accomplished.

This article was prepared for you by Waleed Rishmawi, one of our ‘Master Authors’ and currently working in the Bethlehem area of Palestine repairing electrical and electronic equipment.

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Note: You can check his previous repair articles in the link below:

https://www.electronicsrepairfaq.com/two-k50t60-mosfet-burnt