Migatronic Automig 273 wire feed

[Are]

Hello fellow diy-ers,

I have an old Automig 273 where the wire feed stopped working. Here is what I have tested so far:
- Strong arc when handle is pressed.
- The wire motor it self is working when connected to 12V.
- With motor disconnected I measure correct voltage over the wires going to the motor, but with motor connected the voltage drops to zero.

As you know the plus side of the wire motor is connected directly to the welding current, and because the arc is strong, I assume that the plus side is ok. So the problem seems to be on the minus side, probably on the pcb somewhere. There are no obvious defects like swelled caps or burn-marks on it. Does anyone have a suggestion where I could start looking?

Any help would be much appreciated,

-Are

 

[eddie49]

Hei and welcome to the Forum !

I have found a Migatronic Automig manual online, and it does have a block-level circuit diagram, but it is an inverter.
I assume that your machine is a traditional transformer-based model. Do you have a manual for it, anything that shows how the internal wiring is connected?
Without that, it will be necessary to trace both wires from the motor to the PCB, and identify which pins or terminals they connect to.
When doing that, check that there are no bad connections that would cause a high resistance and drop the motor voltage under load.
Then from clear photos of both sides of the PCB we can start to reverse-engineer the circuit diagram.
Alternatively, from a photo of the component side and with a list of the device numbers of the high-power semiconductors ( basically, those on heatsinks ) we can guess which ones drive the wirefeed motor.
Regarding the power source for the motor: on a machine of this size and quality, especially on a 3-phase welder, it is usual for the wirefeed and control logic to have a separate auxiliary power supply. Please look for a medium-size transformer with 230/380v input, 24v output, with a bridge rectifier, smoothing capacitor, voltage regulator, somewhere...., and verify that the output voltage is stable.

 

[Nix2]

Here is the original wiring diagram, but I do not have the control board diagram.

 

[eddie49]

@Nix2, dziękuję bardzo for that circuit diagram.
It shows that as I guessed there is an auxiliary transformer, with 230v and 400v inputs and 24v output.
The control board ( or box ) is connected via the typical Migatronic "DB9" 9-pin plug. There are other Migatronic threads on the Forum that include diagrams for the various models of control boards that use that connector.

 

[Barking Mat]

Probably the relay which supplies 12v to the motor ?

Something to check, is 12v being supplied to the relay ?

Is it clicking when you pull the trigger ?

 

[Nix2]

Probably the relay which supplies 12v to the motor ?

The engine will of course run on 12V, but it is usually a 24V DC engine.

 

[Are]

Hello,
Thank you for all the suggestions. It's working again after buying a new circuit board, amazingly they had it in stock at the semi-local dealer. Before that I backtraced and tested the power-parts, manly the caps, two resistors and the two mos-fets, without finding anything wrong.