JowettTalk

My PARWELD TIG XTI200 equipment decided to blow up last week after a wire connected to a circuit board fell off due to poor stripping or non-removal of flux from joint. Anyhow it has taken out one or more of the MOSFET IRFP 264N semiconductors. The PARWELD distributor wants £150 for a new board, so I investigated replacing the parts myself. Use of the multi-meter to check the 40 MOSFETS in the Output inverter seems to show two of them are faulty. But to be sure I need to know how they are configured so I am trying to find a circuit diagram.

This is the best so far.
http://igor.chudov.com/projects/Homemad ... er.IRF.pdf

I started my career in the semiconductor industry when it was just starting in 1970. The industry has moved on considerably and most of this paper is outside my comprehension!

The last time this happened, which was on my computer, Scott managed to source the semiconductors in California and sent them over. That was a difficult soldering job on a multi-layer circuit board. Hopefully this is easier.



So we do not just mend Jowetts.

Yipee!!!
The MOSFETS came today and my mate , Bill, came around to offer encouragement and some knowhow. Chris also popped in. Well after splitting some logs I went to the garage after reading some more on how to test MOSFETS. Although previously I had used the resistance (ohms) setting and measured in both polarities between all combinations of gates , this time I used the multimeter on the diode setting with the negative on the gate and positive on the drain. This gave a reading of 1.3 on all the good banks of transistors but 1.06 on the bank with one bad MOSFET removed. Removing the other bad one brought it up to 1.27. Care had to be taken with the solder sucker as the copper on the circuit board easily lifted. The Metal Oxide Silicon Fire Emitting Transistor
The red wire that had broken either due to acid solder flux or bad wire stripping.

The backs of the semiconductors were coated with heat transferring substance and then the legs were carefully inserted through the circuit board. Then the clamps were bolted down to 10lbf-in or 1.1Nm. Soldered in, the multimeter gave the desired reading of 1.3. So testing time.

Yep it now works. Not that I tried it for long or on high amperage. But it now created an arc at 30 A which it did not do before.

Good enough to celebrate. So the men in Honk Kong sent 10 of these devices to me and I only used two. Hopefully I will not need the other 8. Saved myself £130 and gave myself lots of satisfaction at fixing something at a discrete level rather than changing a board. Total cost of repair £4.50

Whilst researching components I happened to click on a link that took me back to the first company I worked for. TI. here is the link very useful to get rid of unwanted noise. I wonder if it works on back seat drivers. http://www.ti.com/solution/active_noise ... lation_anc