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A Shorted Welding Machine Repaired-Model Force 145

By on August 15, 2017
fluke meter zero ohm











I have been getting a lot of electronic welding machine for repair. May be it is due to the high heat wave we are getting. It had a nasty short on it. Let me explain.

welding machine repair

This is the external metal cover. And as you can see, it is very small yet very efficient in power.

It goes up to 130 amps.

welding machine circuit board

That is an inside view of the machine. It has a lot of SMD parts on it. No surprise there since it is very small. First thing I usually do when I get such machines. With the Machine off, I switch my multi meter to ohm or continuity settings and test the two positive and negative terminals.

how to fix welding machine

If it is shorted out, it will give you a very low ohm reading or the meter will beep if it is on continuity settings. In this case, it beeped which is an indication of a very serious short on its output transistors.

fluke zero ohm

welder machine repair

These were shorted out. The part name is STTH6003CW and I had to replace both.


This part was also shorted. The part number is GP4068D. There was also another part just like that just the opposite side of this part.

how to repair welding machine

These parts are very hard to find. The only place I could find them was on Alibaba web site for really cheap price. The only problem it will take about 20 days to get here. The customer was willing to wait. I set the order and it came in twenty days as expected.

After I replaced all four parts, and when I measured, the short was gone. I noticed there was also a resistor missing just by the power area.

fixing welding machine

The only ways to find the value of this missing blown resistor is by comparing it to another similar one or get the schematic for it. Finding a similar machine in our area was not a hard thing to do.  The value was 150 ohms 15 watts. The strange thing is I could not find the actual resistor inside the machine. I am assuming someone tried to repair it and did not bother to put the part back. That is my only guess. Either way, the machine is fixed and the customer was happy to get it back alive.

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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  1. Robert Calk

    August 15, 2017 at 1:10 pm

    Good job, Waleed.

  2. Parasuraman

    August 15, 2017 at 4:03 pm

    Very good job! Thanks for sharing!

  3. Albert

    August 15, 2017 at 4:42 pm

    An impressive small Italian made welder machine indeed Waleed, this Telwin Force 145!
    If these welders completely short circuit a lot I wonder if the manufacturer had tested them thoroughly before selling these worldwide? Seeing most important Mosfet semiconductor parts were all destroyed, smaller could also mean higher chances of machine failures because of higher internal temperatures.

    • Albert

      August 16, 2017 at 10:54 am

      I also have a 140 Amps 220VAC Welder machine that never fails because it only has one very large transformer without any semiconductorboard in its circuit like the Telwin Force 145 shown. But these are probably more expensive to make nowadays because of the large, big and heavy transformers?

      • Waleed Rishmawi

        August 17, 2017 at 8:48 pm

        Albert: yes, these machines hardly ever fail but the main problem is they are too heavy to carry, they use a lighter ones that works with semiconductors and fail very often.

    • Waleed Rishmawi

      August 17, 2017 at 8:46 pm

      Albert: I am sure the manufacture test them out but the main problem is they do not fit to work with power generator and that is why it gets shorted out. they put a warning on the manual not to use the machine with power generators but it seems like not every reads the manual before using.

  4. Yogesh Panchal

    August 16, 2017 at 12:44 am

    Good job!,Waleed.

  5. Henrique Jorge Guimarães Ulbrich

    August 16, 2017 at 2:49 am

    Good job, Waleed. I'd never repaired this type of machines. Just one doubt: you have said that STTH6003CW is a transistor, but in fact it is a double diode used as secondary rectifier.

    • Waleed Rishmawi

      August 17, 2017 at 8:34 pm

      I stand corrected. thanks for your input

  6. Bibhas

    August 17, 2017 at 5:22 am

    Hello Sir, very good job.

  7. Hicham CHAMSI

    August 18, 2017 at 6:27 am

    Hi Waleed. My congratulations for your great job. You have done a good effort to fix the welder.
    In fact the almost issue who can happen is a shorted secondary module who is here in telling brand are the two fast diodes for n 1 package. Often there are 6 of TO247.
    But the most difficult for me is yellow led on or flickering in other brands and no output voltage.
    AnywAy thanks for sharing.

    • Waleed Rishmawi

      August 21, 2017 at 4:54 pm

      Hicham: thanks for nice comments. about the yellow light steady or flickering which is an indication of over heating in the device or one of transistors, or diodes are shorted out. also you will get a zero reading on the red and black output of the machine.

  8. Hicham CHAMSI

    August 22, 2017 at 10:52 pm

    Perfect Dear Waleed.
    Really happy to know the professional tech-engineers like you. Thanks and I wish you good continuation.
    Best Regards

  9. Tesla

    October 22, 2018 at 9:35 pm

    Good job sir.
    I have the same model welder, donated broken to me and I fixed it by changing the IGBTs and secondary diodes also. It works but i can't set the current cause the board was "touched" by someone before me and now i have not the potentiometer and the 3 jumpers under the board marked as JP1 to JP3 are clear now.
    Can you give me please some infos for the value of the pot and the jumpers?
    thanks a lot in advance!


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