So I disassembled the faulty (I think) HF unit from my Thermal Arc 300GTSW (Single & 3 phase selectable) tig welder and now trying to figure out how the thing works. I have attached pictures of the circuit board and a crappy hand drawn circuit diagram. Arc is weak and wouldn't ignite on AC mode, DC welding is fine although the arc won't transfer at times. I would appreciate if anyone is kind enough to explain the workings of this board. There is no replacement part so my only option is to repair it and to do that, I have to first understand how it works. All I know is this board is supposed to generate high frequency high voltage as an ignition for the torch arc transfer.

Also need help identifying that 151J part. What's it called, what it does and where can I find the datasheet for it? And why is diode D6 so long? It only has the number 79 on it, which I can't find on the internet. I assume T1 is the low to high voltage transformer? Why does it only have 3 terminals and why is it so small? All other info I searched on the internet on TIG HF starter circuit showed them to be pretty big and hefty like they weigh a pound or two. Is SSS a regular diode? It does appear to behave like a diode on my multimeter. Why is it bigger than the rest?

 

Continued for pictures and diagrams. Full service manual can be found at:
https://www.manualslib.com/manual/794240/Thermal-Arc-300gtsw-Pro-Wave.html

 

Hi.
I suppose D1,D2,D3,D4 to be a bridge rectifier. C1,C2,D5 et al a voltage multiplier of some sort. The 151J to be a current limiting resistor. T1 another current limiter. C3,C4,SG1 and the transformer to be a tank circuit just like the tesla coil schematic in wikipedia.
https://commons.wikimedia.org/wiki/File:Tesla_coil_4.svg#/media/File:Tesla_coil_4.svg