Problem with a 1986 Migatronic 350 MIG Welder

  1. sgagro New Member

    Hello, to all members,I'm New in the forum and i need Help about my fsther's Migatronic 350
    As he normally weld,sometimes makes a "grizzly sound and it can not provide the specific amperage
    Because my occupation is electrician i Have a some view on transformers, rectifier and etc but I'm not sure where the problem is
    Can you help me?
    I will appreciate that
    Thank you
  2. eddie49 Member

    Hello sgagro, and welcome to the Forum !

    From your description of the intermittent noise and power drop, it is possible that one or more of the diodes in the rectifier is breaking down, going either open- or short-circuit, and the noise is due to half-wave AC....
    You could check the diodes with the "Diode Test" range on a digital meter, but that may not show any issue because the fault is intermittent. Does the fault happen more often at the higher power ranges?

    You could check the voltage at the MIG torch tip - it should start about 15v and rise to 35v DC as you step up the power ranges.

    The main welding transformer is usually switched on by a large heavy-duty relay - a Contactor. After a long life, this could be faulty, with burnt contacts, a failing coil, or a sticky actuator - which could buzz.

    Is this a step-switched MIG, with one or more multi-position range switches, or is the power adjustment fully variable with a potentiometer? The latter Migatronic machines use SCRs ( thyristors ) to rectify and also control the output power. A random failure in the trigger circuit could make that kind of buzzing noise.

    You could also look inside the machine for any loose, burnt, or corroded connections, especially in the high-current output circuits.
  3. sgagro New Member

    Hello eddie49, Thanks for your time and information about my problem
    Yes, it is a step-switched MIG with two Rotary Cam Switches
    I think that the problem is created by the contactor
    I found some burned spots on its contacts