That's an inverter welder. The three AC phases are rectified to DC to charge a bank of capacitors before a DC to DC inverter by 6 diodes. That section of the welder can be run using 2 of the 3 AC input leads leads. Only the 4 of the 6 input diodes will be used, so limit welding current to 2/3 max welding amps. ( unless input diodes are high enough rating. Hint: look at schematic of single phase unit, are diodes same part as 3 phase unit. ) low voltage to operate controls comes from a transformer across 2 of the AC input leads. If no display try L2 & L3. If still no display try L1 & L3.
That's an inverter welder. The three AC phases are rectified to DC to charge a bank of capacitors before a DC to DC inverter by 6 diodes. That section of the welder can be run using 2 of the 3 AC input leads leads. Only the 4 of the 6 input diodes will be used, so limit welding current to 2/3 max welding amps. ( unless input diodes are high enough rating. Hint: look at schematic of single phase unit, are diodes same part as 3 phase unit. ) low voltage to operate controls comes from a transformer across 2 of the AC input leads. If no display try L2 & L3. If still no display try L1 & L3.