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Migwelder wire feed control

Discussion in 'General Electronics Discussion' started by Wayne Phillips, Feb 13, 2018.

  1. Wayne Phillips

    Wayne Phillips

    61
    1
    Jan 7, 2018
    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.!!!
     
  2. Minder

    Minder

    2,722
    565
    Apr 24, 2015
    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.!:p
    M.
     
  3. Bluejets

    Bluejets

    3,091
    604
    Oct 5, 2014
    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.
     
  4. kellys_eye

    kellys_eye

    4,286
    1,143
    Jun 25, 2010
    Got any pics?
     
  5. Wayne Phillips

    Wayne Phillips

    61
    1
    Jan 7, 2018
    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!
     
  6. Wayne Phillips

    Wayne Phillips

    61
    1
    Jan 7, 2018
    They did say it's the motor..nope as a 12v supply has been used to check it and spot on.
     
  7. kellys_eye

    kellys_eye

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    1,143
    Jun 25, 2010
    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.
     
  8. Wayne Phillips

    Wayne Phillips

    61
    1
    Jan 7, 2018
    All these checks carried out..even fitted replacement 470k pot.

    Still did not work.

    Plus took the time to trace out the whole circuit.
     
  9. kellys_eye

    kellys_eye

    4,286
    1,143
    Jun 25, 2010
    Change the chip - probably an LM324?
     
  10. Wayne Phillips

    Wayne Phillips

    61
    1
    Jan 7, 2018
    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.
     
  11. kellys_eye

    kellys_eye

    4,286
    1,143
    Jun 25, 2010
    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?
     
  12. Wayne Phillips

    Wayne Phillips

    61
    1
    Jan 7, 2018
    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!
     
  13. Wayne Phillips

    Wayne Phillips

    61
    1
    Jan 7, 2018
    Still migwelder fixed and on it's way back to the metal shop...
     
  14. Bluejets

    Bluejets

    3,091
    604
    Oct 5, 2014
    Somehow, these two do not seem to fit together.

    And yet these two do

     
  15. Wayne Phillips

    Wayne Phillips

    61
    1
    Jan 7, 2018
    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..

     

    Attached Files:

  16. curtis shiffer

    curtis shiffer

    3
    0
    Feb 16, 2018
     
  17. Wayne Phillips

    Wayne Phillips

    61
    1
    Jan 7, 2018
    Yeap..I did type this last comment in the early hours of the morning..
     
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