gys wire feed potentiometer

  1. eddjones99 New Member

    Hi folks im new here so bear with me, I am capable of doing basic electronic and mechanical repairs to most things in life, but im stuck on this:- The gys welder im working on at the mo has a red, white, and black wire going to the board that has the wire feed speed potentiometer soldered to it, someone had snapped the knob off the front taking with it the shaft of the pot. I replaced pot like for like ,mine was a 100k, and i noticed a small trim pot soldered to the board on the black wire side , which makes the resistance between red black adjustable and the resistance between white and black adjustable . The reason im asking is i may have accidentally turned/moved trimpot while handling which will alter two of those resistances as stated earlier. This has to be there for a reason , does anyone technical know the resistances. I can roughly alter main resistance of pot from 100k to 105k or 95K and i can alter zero ohms on main (middle pin and red) connections to read 4k when wire speed pot is supposed to be on zero. I need clarification on this i dont want to damage main board. Any help would be great thanks.
  2. eddie49 Member

    Hello and welcome to the Forum!
    In general, where the control PCB of a MIG welder has a trimpot in the wirefeed speed control circuit, it will be there to set a minimum or maximum motor speed. This part of the pulse width modulated ( PWM ) circuit will all be low power stuff, before the motor drive transistors. Setting the trimpot at either min or max will only alter the pulse width. If not set correctly, it may limit the speed setting achievable by the main front-panel pot, but it won't blow anything up.
    I would suggest setting the trimpot to the mid-point, but if you need more specific data:
    - the main pot is 100K, what is the value of the trimpot?
    - does the trimpot have three separate connections to PCB tracks, or is the wiper and one end of it joined?
    - seen from the front ( shaft ) of the main pot, are the connections red ( left ) , white ( wiper ), and black ( right ) ?
    [ if so, I think that would put the trimpot in parallel across the main pot... ]
    slim_boy_fat likes this.