Electronic welding machine in short circuit

[DisasterNow]

I don't understand how it happened, I just lowered the board while it was under voltage. Of course it could be the signal that goes from the relay to pin 10 of the control board to trigger this Finder on/off. I wanted to do this test just to exclude the relay from the possible causes of the short circuit.
Since the contact became NC at about 120v, I could also simulate it with a flying switch, but I would have to figure out how to connect the other two contacts (from the M10 pin and the 13.7 power supply).

[coppercone2]

something is cracked or loose, it must be sagging or flopping or tilting

bad contact is most likely


I bought more conformal coating remover after watching some videos of transistors burning out from over current through a microscope, some little valve is likely vaporized on my welder so its fixable. I was getting seriously over whelmed thinking about the problem, but when you see that its essentially replacing a fuse some where, it gave me some strength 

Its the cost of doing business I guess, like having to remove nuclear waste or raking leaves.

[DisasterNow]

But is it your circuit board in the photo?

Yes, it could be a loose contact, in fact I was lowering it with the insulated handle of the screwdriver and when it took the small kickback resting on the table, the relay started this on/off. Maybe that short circuit increased and the control board inhibits and enables the relay continuously now. I want to understand how the relay engagement sequence occurred at startup, slowly increasing the voltage with the variac is easy to understand and then I want to try to make the contact of the relay manually with a switch at the right time, just to exclude that the relay could have problems (in addition I unsolder and re-solder it, which is not a bad thing).
I also want to unsolder the two large filter electrolytics, and also measure their ESR, they are many years old (20?) and maybe they could be the cause of problems, who knows.
Then I will seriously start to unsolder the power part, also because I was wrong, everything is inhibited if I have the potentiometer at minimum (not maximum as I had stated), and as soon as I increase the power, the short circuit appears at the same time that the control board enables the signal on the pulse transformer and consequently the IGBTs start to work and in fact with the short I start to have an output voltage.