Hello there.
I have a Sunkko 737G Spot Welder, cheap noname chinese device, that I just bought off Ebay. First time turning it on, it worked. Then I turned it off, inserted the foot pedal switch (not sure if that's related), turned it back on and the device popped: Huge bang, fuse of my home installation tripped. After untripping the fuse, the device is completely dead. There is a fuse 20x5mm inside the device as well, rated at 20A, which did not trigger.
Upon inspection of the device, there seems to have been a fault right at the very first component the AC goes into: The way this is built, AC goes to the PCB, which via a Triac (BTA41) activates a transformer (which creates the high amps for spot welding). What seems to have failed is an SMD component in series with line. The issue is the component has spectacularly failed and been obliterated and evaporated. No chance of identifying it (pic attached).
My two questions now are: What could that component have been? And, more importantly, is there a root cause that made it fail, i.e., what circuit behind it drew so much current? Interestingly, none of the components on the other PCB side appear damaged or having seen lots of current. The electrolytic cap looks a bit pregnant, but it's measuring no short. There seems to be an SMPS circuit and the small blue transformer measures very little resistance on both the output and the input (order of less than 1 Ohms). I would have expected at least something in the 100-1k range. Could that be the defective component? Optically it looks fine.
Any idea what the secondary voltage could be? Because then I could cut out the whole dodgy SMPS circuitry and just bypass it by a second SMPS, there's enough space.
Any advice welcome!
Cheers!