migatronic 305

  1. Rhys134 New Member


    Wondering if anyone can point me in the right direction! I've Got an issue with my migatronic 305. Welder is feeding wire but no arc. Contactor is not operating but appears fine but there is no voltage present at contactor when the trigger is pulled. Will arc when manually pushing contactor in.

    Is it the PCB board? Looking at the diagrams there is only one switch "1-10" on the orange wire feeding the contactor, what is this switch?

    Transformer has output voltage on the various legs so assumes fine.

  2. eddie49 Member

    Can you see what coil voltage is marked on the Contactor? Typically 24v DC or 240v AC.

    If DC, the power for the Contactor would come from the auxiliary 24v DC supply, via a relay on the PCB.
    If AC, then that could also be via a relay on the PCB, or by a Triac. Often the circuit diagrams do not show detail of the PCB internals, but it should be possible to troubleshoot visually by looking for stuck relays, burnt contacts on relays, tracing wires, and checking part numbers on any 3-lead power semiconductors to confirm a Triac.

    You said that wirefeed is OK, and arc works if the Contactor is operated manually. What about the gas valve?

    Oh, and welcome to the Forum !
  3. Rhys134 New Member

    Thanks for the Reply, I never noticed if the contactor was Ac or DC ill have another look. The gas wasn't turned on either when I was overriding the contactor so will check that as well.

    Looking at where the orange wire goes to ( the display board) I cannot see any footprint for a relay T4 could possible be the triac. welder PCB.PNG wiring diagram.PNG
  4. eddie49 Member

    It's good that you have got a copy of the wiring diagram. I think that "1-10" may just be a link, or a pin on a plug, rather than a switch.
    It would be useful to know the coil voltage for the Contactor, and also the voltage for the gas valve. When pressing the trigger switch, it may be possible to hear or feel the gas valve opening. If the control circuit for that valve is still OK, or is separate from the control circuit for the Contactor, then it should be opening or closing on trigger press regardless of the state of the Contactor. In theory, the gas valve, the Contactor, and the wirefeed motor will all be controlled by the same circuit - although maybe not if the machine is fitted with Burnback delay.
    You mentioned tracing the orange wire from the Contactor to the "Display" board.... I would expect the wire to go to a control and motor speed board, containing at least some power transistors ( plus heatsinks ? ) for the wirefeed motor speed controller. That is where we could find the small relay, or the Triac, that triggers the large Contactor. A Triac is usually packaged in a "TO-220" component outline, which has a metal mounting tab:
  5. Rhys134 New Member

    I wonder if it just passes through through the display board as this seems to handle the overheat triggers and i'm guessing it drops out the contactor in the event of an overheat.
  6. eddie49 Member

    You are right, from the diagram above, the orange wire from the Contactor coil goes via item "1-10" ( whatever that is ), is labelled "PSRUN", then to Pin 5 of Plug M2, which is a 10-pin plug on the Indicator/Fan Control board.
    The other end of the Contactor coil is wire U12, brown, and it goes to the 23.5v AC side of the auxiliary transformer.
    The 0v side of that transformer, wire U10, grey, goes to pin 2 of Plug M2. This implies that the coil of the Contactor runs on 24v AC.
    If you put a link from pin 2 of Plug M2 to pin 5, the Contactor should pull in.
    The circuit diagram does not show the gas valve, nor does it show the Eurotorch trigger switch.