Migwelder wire feed control

[Wayne Phillips]

I was asked by the local welder to look at his migwelder as the wire feed motor and the control board was acting up.


1) when trigger was pressed in, it's wire feed circuit board could be heard working.

2) you had to adjust the control all the way round before the wire would feed out.

So, off with the covers and on show are two large bulky power transfirmers and a small feed board.

I tested the 24v dc wire feed motor with a power pack and all good there, so time to remove the control pcb and try a few things out.

Chagned the 470k adjuster pot followed by some old caps and give the pcb a good cleaning. After fitting the pcb in it still was only half working and pointing to the c mos smd chip.

My phone call to the welding tech shop was less that helpful and in there word's

"We poke and probe till something works"

Must be a new tech sort of term poke/ probe..


In the end I did order a new pcb at £130 qid and I did not wanted to spent to long on this unit.

I still have the old wire speed pcb..

Still all working now.!!!

 

[Minder]

Is there a question in there?
BTW poke and probe is an old method used extensively in the past, 50/50 on whether it works.
The other is replace every thing one at a time until it start to work again.!
M.

 

[Bluejets]

While you are poking and probing, either clean/ or better still, replace the inner wire guide as this is more than likely the fault area.

 

[kellys_eye]

Got any pics?

 

[Wayne Phillips]

The question was put to repairs department.

There tech guy says yeah we just replace boards and not sure how the chip on the board works!
Mmmm.


Blujets.

when I was being trained in electronics we had to show that we understood how the circuit worked.

Not poke about...words fail me here!

 

[Wayne Phillips]

They did say it's the motor..nope as a 12v supply has been used to check it and spot on.

 

[kellys_eye]

Probably a simple PWM driver. Check the potentiometer isn't open circuit at one end of the track (including cracks in the pcb). Check the switching device (transistor or mosfet) isn't defective.

 

[Wayne Phillips]

All these checks carried out..even fitted replacement 470k pot.

Still did not work.

Plus took the time to trace out the whole circuit.

 

[kellys_eye]

Change the chip - probably an LM324?

 

[Wayne Phillips]

It's a c most 400 somthing.

My scope check check showed square drive to the fet and the fet itself is ok


But when you have a welder chap ringing up and popping round..you just fit a board in for quickness.

 

[kellys_eye]

FET is ok? Then you're getting the same (but amplified) squarewave at the FET 'output' (i.e. the motor)?

Is the squarewave duty cycle varying with the control?

 

[Wayne Phillips]

The control only seemed to work when adjusted to 7 to 9..

The chip is not working as it should..

In the end a new board was fitted as the welder guy moaned about cost!

Well I'm not doing this for the sheer joy!

 

[Wayne Phillips]

Still migwelder fixed and on it's way back to the metal shop...

 

[Bluejets]

Somehow, these two do not seem to fit together.

when I was being trained in electronics we had to show that we understood how the circuit worked.

It's a c most 400 somthing.

And yet these two do

Not poke about...words fail me here!

In the end a new board was fitted

 

[Wayne Phillips]

Just a quick look over that...

Last comment.. the welder chap moaned about cost as on the board.
Bluejets.. we all can spend time looking over a circuit in front of us and get it to work.

This welder cap rings moans and even pops round is it ready yet..

Somehow, these two do not seem to fit together.





And yet these two do

 

[curtis shiffer]

Just a quick look over that...

Last comment.. the welder chap moaned about cost as on the board.
Bluejets.. we all can spend time looking over a circuit in front of us and get it to work.

This welder cap rings moans and even pops round is it ready yet..

 

[Wayne Phillips]

Yeap..I did type this last comment in the early hours of the morning..