MIG welder repair + internals and wiring explained

The trusty 32 year old MIG welder urgently needed some work. The selector switch was stuck at max current and it randomly produced too little welding current.
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It turned out that the fault (actually several faults) was much trickier than it looked at first sight.
We also explain the components inside and the basic circuitry of a 3 phase welder, in particular if used on a single phase supply. Those principles apply to pretty much any transformer based welder, as long it has a real current switch and not just an air gap spindle like the cheap buzz-boxes.
This particular machine is an Einhell SGA 160, most likely produced in the former GDR. I have it from new and it was not cheap at all, but in return it never let me down before. i never replaced anything other than the usual consumables. ..Sadly, things don't get built like this anymore.
In it's days, it was a mid range no-frills machine, initially purchased for sheet metal work. Also did some fabrication with rather heavy stuff, works well, but the low duty cycle at full buzz needs attention.

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www.dynoguy.co.uk

Please note:
Electricity is dangerous and may kill you, therefore consult an expert if you are not qualified, This is not a how-to, footage is for entertainment only.