Einhell SGA 175 Turbo - Low Power, Unstable Welds, Voltage Measurements

Hello you
I have a migomat as in the subject - Einhell SGA 175 Turbo.
Unfortunately, the problem is that he lacks power. Poorly blends, welds made with it are unstable. Another migomat, much smaller has more power than this.
I did some measurements.
The voltage on the secondary winding of the main transformer when welding in the largest "gear" is approx. 31-34V AC. The least was 29V, and the most 49V (it's already "in the air"). Measurements made on the rectifier bridge, right next to the connection.
The voltage on the primary winding is 221V AC (during welding).
What can be guilty of? What measurements do you still need to make?

I will add that the wire feed motor is a bit uneven, it happens that it cannot be started - as if it encountered a break in the connection on the commutator. It helps setting a higher wire feed speed and then starts. However, this should probably not affect welding power.

I hope I have provided you with all the information you need. I am asking for help in determining the cause of this problem.

Pictures:

Check the ground and current cables - contacts and transition.
Check that all current connectors in the trafo-bridge-choke path are clean and tight.
Check if any of the range switch components are burned (check the tightness of the screws holding the wires)
Check the diodes in the bridge (break). Check bridge assembly (slack).
Uneven engine operation may indicate damage to the range switch or the rectifier (feeder motor powered from the main rectifier output)

Enter the DC voltage at the output of the rectifier bridge at each threshold. The feeder never runs stably in a single-phase indicator. Check also whether the wire moves smoothly in the handle or if it goes hard, of course, when the feeder pressure is on and the handle is straightened.

Thank you all for the answers. Now I know exactly what to check

The wire without pressure moves slightly.

If I have more free time I will check everything and of course I will write the answer here.

I also ordered a 200A shunt, when it comes I will see its current efficiency.

Greetings.