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Maxstar 300 dx smaw ISSUES

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  • Maxstar 300 dx smaw ISSUES

    Hello All;
    I have a used circa 2000-2001 miller maxstar 300DX inverter bought from ebay that has a SMAW issue with cooling fan running very frequently and output switch turning off.

    serial # LA030044:
    arc on time is 1905.87 from startup display

    The issue is when the welder is switched ON, no leads connected and I select SMAW output ON switch, the open circuit voltage on the display starts at 89.9 volts and slowly rises digit by digit to 91.1volts (I hear a contactor click), digits keeps rising to 91.6volts (i hear a 2nd contactor click-but louder) and keeps rising to 92.2 volts ( where a high pitched whining sounds starts and both fans start to cool the unit). All this happens within 5-10 minutes, then
    the voltage display settles to 93.8 volts and the fans keep on , and on (30 mins sometimes) until I switch OFF the SMAW output switch or switch to GTAW and within 2 minutes the fans stop running.
    the right side of the unit case is noticeably hotter in SMAW than in GTAW.
    Two other things are happening when the welder is switched on and that is
    1. the 4th red LED (on amps side) is always brighter than the other LEDS-doesn't affect welding
    2. there is a high frequency signaL being given off when in the SMAW output switch is ON and is not present when that switch is OFF ( I was looking at the TV signal while fiddling with the knobs as I was trying to troubleshoot the issue). I get the same frequency signal interference when in GTAW mode -high lift lasts for a 1 sec and HF button gives it when the foot pedal is pressed-which is supposed to happen) don't know why it's happening in SMAW output on mode??

    I started the trouble shooting as when I was welding SMAW last week with 3/32" E-6010 electrodes,at 79amps, 10% dig after the 4th electrode the welder fans started and I got no welding output and No error code display. after 1 hour I still had no welding output, but all the display lights showed as normal.

    I prerused the miller forums for answers/fixes and didn't find any loose bolts, but the 2 torque wrenches I have don't go down to 17 and 20 ins/lbs so I guesstimated the torque, I unhooked all the cable harness and reattached them and was able to trouble shoot the caps c3 c4 and c1 with a fluke 189 multimeter, diodes d1, d2, w1, w2 contactors, the tests were OK, but had trouble with the IGBT's as the miller diag. doesn't indicate where the circuit board bolts for PC2 are located for me to get to the PM1 and PM2 boards to test.

    This week when i got my supply of argon, I hooked up for GTAW and did a tacking job on mild steel using inconel 3/32" rod, 3/32" tungsten 2% Th, at 79amps, pulse on and had no problems with the tacking, no fans coming on and no real heat on the right side of the case.
    When I switched to SMAW to see if I got the welding output back, using 3/32" E6010 at 65 amps and at 79 amps, I got the variation in welding output but I only burned 1/2 a rod to see if I got back SMAW welding output, and again no error codes, and the fans kicked in after a 1 min of welding and kept on running and running. (at least I got back welding output, and am back where I started with the smaw issue)
    So whether I'm hooked up and welding smaw or not welding and I push the smaw output switch I get the same result after the same amount of time and that the right side case gets hot, the fans keep running, no error code generation on display and welding output shuts down sometimes...

    any suggestions?
    I know something has gone south or is in the process of going south and I would like to correct it before it takes out other components and get more expensive to fix

    the pre-power checklist manual I am using refers to Miller testing booklet #150 853..does anybody have a copy of this ??

  • #2
    The 300 has to be one of the WORST machines to troubleshoot. I can't help you


    • #3

      not exactly the info I was expecting, but I appreciate your candor on the unit as I wasn't aware that this model had that type of reputation, probably explains why very few posts here refer to it.

      I was able to continue welding on the SMAW project by using another maxstar 300 (the one you had helped me on with error 13 and is still working GREAT).
      And I was able to also get some additional measurements in so I am still looking for that testing booklet to verify what I found #150 853..

      does anybody have a copy of this ??