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Strange Symptoms On A Welding  Machine Repaired

By on September 8, 2020
how to fix welding machine







A welding technician brought his machine for repair. I was informed that this machine suddenly went into shut down while the welding technician was working on it.

how to fix welding machine

The machine was brought to me with the top cover off suggesting that someone was trying to fix it and somehow it was not fixed.

welding machine repair

The Amp display was missing for some reason and later on I found it inside the machine. If you look to the light indicator you can see the green power light is on and that is normal but the red light is on too and that is not normal. The red light indicates a fault inside the machine.

In a repair like that I usually start testing the Mosfets but for some reason all checked OK.

welding machine circuit board repair

My second step was to check the main board; that is the main brain of the welding machine and this also checked fine.

I worked on this machine for almost two hours straight then I decided to take a break then come back later on and work on it.

The next morning I started working on this machine and anther hour spent without getting even close to the source of the fault.

how to repair welding machine

I checked this area for fault but nothing was wrong there either. Then I decided to take the whole top board off and check it out again.

how  to fix and repair welding machine

As I took the top board off and started checking the Mosfets again but this time I took them all off board. 

As I soldered the far right Mosfet, one of the pins on that part fell down. When I tested it, it was not shorted but it was giving me strange readings. The part number is 23N50E. All other Mosfets checked ok.

23n50es datasheet

Please click on the photo above to access 23N50ES Datasheet

23n50e check ok

Once it was replaced and powered on the machine, the red light was off at this time indicating the fault in this machine was fixed.

I do not usually take the Mosfets off board to be tested I just get the reading then I compare with the rest of the Mosfets. This one tricked me into believing that it was fine and caused me a lot of headache and wasted too much valuable time.

how to check the welding machine output

The voltage readings on the output pins were perfect; I took it to my brother’s welding workshop for further testing. It worked amazingly well.

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:




  1. Menahem Yachad

    September 8, 2020 at 5:40 pm

    As always, a superb job.
    Well done!

    • Francisco Maciel Barba

      September 8, 2020 at 10:08 pm

      "strange readings" like what...?

      • Waleed Rishmawi

        September 9, 2020 at 4:14 pm

        Francisco: strange reading as of the Mosfet was giving me a normal reading but in fact was defective.

    • Waleed Rishmawi

      September 9, 2020 at 4:13 pm

      Menahim: thanks man. good to hear from you

  2. Parasuraman S

    September 8, 2020 at 8:39 pm

    You are a very patient hunter, when it comes to electronic service! Very determined fault finding! Many thanks for sharing!

    • Waleed Rishmawi

      September 9, 2020 at 4:15 pm

      Parasuraman: Patient is a virtue in this type of repair. have a blessed day.

      • Parasuraman S

        September 9, 2020 at 10:11 pm

        You know something, we almost exhaust the stock of our patience on our service work to such an extent that when we come out of it, we become irritant when we interact with our family members! This is an observation made by my elder son, who is with me here on a holiday (An electronic and telecommunication engineer. That's how I realized it!) Our mind is bogged down with problems and solutions on various sets that throng our service Centre that it gets into our nerve, many times unknowingly! Very sad situation!

        • Waleed Rishmawi

          September 10, 2020 at 2:46 pm

          totally agree. somehow we need to separate home and work. Many times my son who is almost ten years old gets fed up with me when I am watching things at home about repair and he goes and tell me: dad you are not at work any more, let us play football.
          so I made a decision not to bring my work into home... and i am sticking to it no matter what

  3. Albert van Bemmelen

    September 9, 2020 at 1:23 am

    Good job on another Welding machine repair done, Waleed! And thanks for mentioning the special Mosfet datasheet.

    • Waleed Rishmawi

      September 9, 2020 at 4:15 pm

      Albert: thanks man. you are most welcome. have a blessed day

  4. Yogesh Panchal

    September 9, 2020 at 3:09 pm

    Well done! Waleed,

    • Waleed Rishmawi

      September 9, 2020 at 9:43 pm

      Yogesh: thanks man


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