A Shorted Welding Machine Repaired-Model Force 145
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.
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.
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.
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.
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.
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.
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.
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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