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A Welding Machine Powers On But The Welding Is Very Weak Repaired

By on March 23, 2024







A welding technician brought this machine to my shop for repair and explained that this machine powers on just fine but the welding on it is very weak even with the amp potentiometer is turned all the way up. 

Rockstone welding machine repair

I powered on the device in my shop and measured the voltages output on the negative and positive terminals of the machine; I was getting 70 DC volts which are normal. I measured the same voltages while my brother was doing some welding on it and these reading dropped almost down to nothing.

In a situation like this I suspected something loose like cold soldering joints somewhere in the machine and based on that I started checking every single joint on all boards.

how to fix welding machine

I started with the IGBT’s pins but soldering was fine there. I checked all the boards and found some cold solder on some joints but I did not think it was causing such an issue because these joints were ok but not the best but I re soldered them any ways.

fixing welding machine

I also checked for bad capacitors on the output stages and the main capacitors as well but they all checked fine.

how to fix a broken welding machine

Then I saw this; could it be that simple? Yes actually that was the main fault in this machine. As seen, both pins on the main AC input were faulty so I changed the whole cable (sorry I forgot to take a photo of it). I took it next door for my brother to test and this time, the machine’s welding was according to specs. I called the customer for pick up so he came right away.


He asked me if he can test it out here and I had no problem with it. So I powered it up for him and he did some welding; he was very pleased with it. A happy pleased customer is my objective and to this I could say

Mission Accomplished.

waleed Rishmawi

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 article on A Dead Steam Cooker Was Restored Back To life. Model: Benaton




  1. Yogesh Panchal

    March 23, 2024 at 3:02 pm

    Good Job!Waleed,

    • Waleed Rishmawi

      March 23, 2024 at 6:32 pm

      Yogesh: thanks man. have a blessed day

  2. Albert van Bemmelen

    March 23, 2024 at 3:54 pm

    The bad 16A/250VAC power plug you showed looked in the photo like a good old trusted European AC plug to me.
    What exactly was wrong with the pins that the photo didn't show?

    • Waleed Rishmawi

      March 23, 2024 at 6:37 pm

      Ablert: it was not supplyiny a stable 220 AC volts to the machine so when the welding starts, the voltage drops, not enough to provide the voltage needed for the welding to take place. if you look closely to the base of the pins, both are cracked and it had to be replaced. have a blessed day

  3. Parasuraman S

    March 23, 2024 at 7:37 pm

    Good fix! You have dared to get it tried out! That requires a lot of courage!

    • Waleed Rishmawi

      March 24, 2024 at 1:45 am

      Parasuraman: thanks man. Have a blessed day.

  4. Imoudu.O

    March 24, 2024 at 3:41 am

    I have been waiting for long an opportunity to handle one weildering machine and this came last Monday.However, having replaced what i thought i should replaced and power on, there was a loud bang, so i passed it over to an expert techican who latter did a good job.First attempt failed,but i believe subsequent attempt i will succeed.Thanks for sharing.

    • Waleed Rishmawi

      March 25, 2024 at 3:08 pm

      Imoudu: if you dealing with shorted mosfets or IGBT's usually you have to test if there are shorted parts around that area. usually some parts will get shorted along with these parts so you need to look out for them.
      that is ok though, you learn and you move on and the next time look for these shorted ones before power on the machine. always use a current limiter to test to make sure there are no more shorted parts left in the machine. if you have any questions feel free to ask and I will try my best to help you out. have a blessed day

  5. mevias

    March 26, 2024 at 8:05 pm

    afternoon sir, long time i have welding machine which as lgbt transitors,the problem is when i switch on the machine is coming on but it cant weld.
    what could be the problem.

  6. Waleed Rishmawi

    March 30, 2024 at 4:10 pm

    mevias: does it show the over heating warning light? if it does usually shorted components on board. does it power on fine? is there a voltage reading on the output of the welding terminals? if not? check the Diodes and the components around them. I need more info so I can help you out. have a blessed day


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