Millermatic 200 blowing the 5 amp fuse
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  1. #1
    Join Date
    Apr 2006
    Location
    CT
    Posts
    1,719

    Millermatic 200 blowing the 5 amp fuse

    Started a new job for rigging outfit and working on a trailer, It's in the project section, I found out owner had and old MM200 buried in storage and didn't know much about it. So I pulled it, cleaned it some and convinced boss to throw a few coins at it, Wire, regulator flow meter, and some tips. Plugged it in and did a few practice welds on scrap, lots of power so let's put it to work. Well 5 minutes into it, lost 5 amp fuse, no fan, wire feed, no arc. So searching says try to eliminate the SR1 or bridge rectifier or such. Haven't had a chance to do that and won't till a little later. Can't remember because I only had 1 spare fuse but I think when I changed the fuse and powered it it held, think it was when I pulled the trigger it blew the new fuse. Any ideas?
    Machine is serial JF919390
    also going to look up year of unit. To bad, I hope it's not to bad to fix, nice little unit.
    Don't know if it matters but it's got over 50 foot of input cable on it, could that make it draw more than it should, Usually that would trip the load center breaker.
    "Si Vis Pacem Para Bellum"

    Lincoln Idealarc 250 AC/DC
    Millermatic 251 Syncrowave 300 30A spoolgun
    Lincoln MP210
    Hypertherm 45
    (2) LN 25
    (2) Lincoln Weldanpower 225 CV
    (4) SA200 1 short hood SA250 SAM 400

  2. #2
    Join Date
    Mar 2014
    Posts
    327

    Re: Millermatic 200 blowing the 5 amp fuse

    Built 2nd half of '85

  3. #3
    Join Date
    Mar 2010
    Location
    Ceres, California
    Posts
    3,381

    Re: Millermatic 200 blowing the 5 amp fuse

    Sr1 is ok if fuse does not blow on power up. Try removing the pcb then power up and pull trigger.
    You may have a short on the pcb. Fairly easy to fix. Just have to find the short. The pcb gets full power when CR1 pulls in.
    But Check the drive motor, there may be a short in its wiring. The fan should not turn on until the welder warms up.
    A rare shorted "W" contactor also could be a problem. So get a box of correct fuses. unplug different things and see what the problem.

  4. #4
    Join Date
    Apr 2006
    Location
    CT
    Posts
    1,719

    Re: Millermatic 200 blowing the 5 amp fuse

    Will do, have to play with it in between jobs when I get some time. Should be a good machine, the little welding I did with it was good.
    "W" contactor? You mean the main contactor where power comes in to unit?
    fan can be checked by isolating and applying power , yes? AC, DC volts?
    "Si Vis Pacem Para Bellum"

    Lincoln Idealarc 250 AC/DC
    Millermatic 251 Syncrowave 300 30A spoolgun
    Lincoln MP210
    Hypertherm 45
    (2) LN 25
    (2) Lincoln Weldanpower 225 CV
    (4) SA200 1 short hood SA250 SAM 400

  5. #5
    Join Date
    Mar 2010
    Location
    Ceres, California
    Posts
    3,381

    Re: Millermatic 200 blowing the 5 amp fuse

    The "W" contactor is the large contactor that pulls in with the gun trigger.
    Turns welder weld power on. Yes the fan can be powered. runs on 115 volts. or find the thermostat on the weld diode heat sink and short it out. fan will turn on. So a shorted fan will not cause a problem until the welder heats up and turns the fan on. Fuse blowing when trigger pulled could be a shorted "W" contactor coil or a shorted gas valve coil. Or a wire shorted in those circuits, Bad drive motors are rare. bad motor should trip the circuit breaker.
    The diagram shows a DC motor with field coils. needs 115vdc to make a magnet, then you can apply voltage to the armature and run the motor. SR 1 diode supplies the field voltage and power to the pcb. pcb supplies the voltage for the armature. CR1 relay turns the motor on and supplies the brake. You can unplug the gas valve and the contactor and try to run just the motor. See if the fuse holds. If it does then plug the contactor back in and try again.
    Then plug the gas valve in. fuse then might blow showing the gas valve is bad. If you have an amp meter you can measure the coil current in the contactor and gas valve. Good coils won't draw much current. When testing the motor release the drive pressure wheel so you are not pushing wire. If fuse blows or breaker trips while pushing wire, the liner is bad.
    After all of this it is possible the fuse blew because of old age.
    Have fun and be careful.

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