Wire feed motor won't work!

[rocketmanken]

I'm new to this forum and new to Mig welding. Just picked up a small machine from my father-in-law. It's an American Forge and Foundry Power Mig 140. My problem is the wire feed motor isn't working. I tested the leads running to it and there is voltage here when I press the feed trigger (varies when I adjust wire speed) I also tested the motor by applying 12V to it and it works fine. How can the motor not run when there is voltage to the leads? From other threads I gather it may be the control circuit (PC?) Anyone have any ideas?

 

[the snooper]

try a 12 volt bulb at the motor feed wires it should light up. sometimes voltage can be shown to be correct but there also has to be amperge to power the motor

 

[pointer2null]

Also check the wires to the motor, a bad connection would mean you'd measure 12V but as soon as you try and draw power the voltage would drop to near zero.

 

[rocketmanken]

Thanks. If it's an amperage problem, does this lie in the control board?

 

[rocketmanken]

My father in law visited and checked out the control board for me. said it probably is the SCR - part # SGS 28601 BUV46 ?? (taken from the part itself). Problem is, can't find the part anywhere. Probably out of production and can't find a cross reference. I have no idea of the specs for the part. Anyone know where I could get the part or a reasonably priced control board?

 

[the snooper]

if it is the relay you dont have to have the exact relay as long as its the same operational voltage and can handle the switching voltage and amps to get by you can solder wires from the board to the relay doesnt have to be pcb mounted relay

 

[R Kraft]

It's probably just a transistor, though it doesn't seen very appropriate :
http://www.st.com/stonline/products/literature/ds/5394.pdf
It looks like a TIP35C is user on the Sips as an output transistor.
Robert

 

[eddie49]

References for the BUV46 state that it is a high-voltage NPN power transistor, in a TO-220 case. With ratings of >400 volts, 6 amps, and 70 watts, it seems a bit over-kill for this motor drive application. If it's blown, I'm sure any reasonable NPN plastic-packaged power transistor from Radio Shack ( do they still sell components ? ) would do the job.

 

[pointer2null]

The rating are not excessive. It was probably chosen for the current capability so you'll need something with a collector current of at least 6amps. The 400V is usually the max collector emitter voltage the device can withstand. It's high because if the motor drive is a pulse width modulation type it works by sending short pulses to the motor. After each pulse there is a large back EMF spike which can easily blow a lower rating transistor.

 

[rocketmanken]

Thanks everyone! This helps. I will try another component with the same specs.