Strange Symptoms On A Welding Machine Repaired
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.
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.
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.
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.
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.
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.
Please click on the photo above to access 23N50ES Datasheet
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.
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.
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: