I took a look at the transformers in my machine. Some have the winding numbers and some don't. The 220Vac is rectified using module rectifiers to create an output DC. Then it is chopped using Toshiba K2698 MOSFETS and a SG3525 type PWM controller to create a 100KHz AC output. That is fed to some Sanken FML 33S diodes to create an output DC. That is fed to an H-bridge to create the weld voltage and frequency using IRFP264 MOSFETS and a controller board. This machine only does TIG and MMA. No plasma cutting. I think the first stage of AC created is around 100KHz because the transformers look to be too small for 20KHz.
On the front of the machine there is a pot labeled "5 Hz - 2.2 KHz". I am guessing that it does adjustable output AC frequency. It doesn't have the peak and basic current knobs so I don't think it is for pulsing. It only has one current knob.
The HF start board has a transformer, small coil, high voltage caps, and copper contacts for the spark gap. Yes, the copper points will wear and need adjusting. I am surprised none of the manuals talk about adjusting them.
One of the structure plastic supports holding the large alum. heatsinks was broken. I am fixing that when I put it back together. The parts won't be here until Monday though to fix the PCB with the FML 33S diodes on it.
EDIT: Changed 20KHz to 100KHz
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