Shorted IGBT K50T60 and 1N4744A In………
My brother entered my shop carrying his old welding machine and explained that his machine sometime weld and most of the time does not. I have worked on that machine many times and from what I experienced, there are a lot of joints that are connected together with wires.
The green board has to come off and check every soldering joints and connection and make sure all are solid.
After taking the printed circuit I ended up with the big heat sink that has all these isolation pieces on.
As I was checking all the joints and connections, I came across many parts that are loose and when I checked with my multi meter, the diodes were shorted and some resistors were open.
I was shocked to see these bad parts and in my mind I knew that the main IGBT’s are shorted too because they are part of the same circuit.
That is a view from the other side of the printed circuit and you can see the damage there as well.
In order to replace all the shorted part, the wires connected to that part have to come off too. I really had a hard time working on that machine but it was a challenge set before me to repair it.
More parts are bad and had to be replaced on this side as well. The yellow and the black wire are there to complete the connection between the IGBT and the main resistor.
These were the total damaged parts: four diodes 1N4744A. A two 10 ohm resisters that were open and two K50T60 that were shorted out and all were replaced with the exact part numbers.
You may click on the above photo to check on the IGBT datasheet
You may click on the above photo to view the Zener Diode datasheet
Finally I got the machine up and running. I was getting the 25 volts at the negative and positive terminals of the machine.
I do not know what happened with this welding machine. According to my brother, it was welding on and off and when I opened it, it was shorted and completely dead.
And as we know by experience, getting voltages at these terminals is just an indication that the machine us up and running but that does not mean it will weld. The best is to try it out so my brother took it to his shop next door and gave it a try and it passed with high stars.
I gave him an advice to buy a new one because it could fail any minute due to the fact it was falling apart inside.
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: