Think of the unit as two separate circuits. One is the main welding power cct.
Power comes in, is controller via the main contactor, then goes to the main transformer, from this to the rectification diodes and the output smoothing caps and then on to the torch.
The second cct is the control circuit, this is powered by the smaller transformer and controls the wire speed and energises the main contactor when the trigger is pulled.
Power is controlled via the switches that select different tappings on the main power transformer (this is basic switching nothing more).
If you push in the main contactor you will be energising the torch.
So a simple test is to hook a meter to the torch and then push the contactor in. If you get welding voltage then you know that the main power cct is working and the issue is in the control cct. Or visa versa.
Ok this sounds simple enough. so I just pull apart the trigger and test there.. or will it be better to test at the euro socket .. I know your going to say euro socket lol