Hi need help have Chinese inverter mig stick 180 welder that blows the four mosfets on gate drive board soon as strike a arc, can’t find replacement mosfets they are marked K50t60 and HAU209 under part number what ever that means, when looking for replacement all that comes up is IGBT. The pinouts on circuit board are marked GDS and on main circuit chart show a depletion N channel mosfet any help or advice on where to find these and why they are blown replaced the board with new one once along with mother board blew again soon after arc struck. Will try and post pictures. Q1 through Q4 are blowing.Thanks for any help.