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Welder failure to power on

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  • Welder failure to power on

    Own a Miller matic 211
    S/N: MF421149N

    The machine first shut down automatically on a initial tack weld. I presume it was a cord disconnect as i had some commotion around me.

    Checked everything out. Reset the power switch, and the machine powered on.

    The next tack also shut the machine down and will not power on now.

    Neither tack weld ,auto shutoff , action actuated the re-settable C/B.

    Coincidentally, i had a rotisserie motor stop functioning on the same circuit. Got distracted with it but that motor continued to work:
    Got shocked on a 12v ground during trouble shooting.....which led me to check my outlet voltage.

    I did some voltage checks on the outlets. The Voltage varied during 20 mins from 190-215 (I Live in Philippines where 240v is nominal), i had 3v-30v volts on the neutral an ground side during that time also.

    Called out the Electrical Company and the lineman found corrosion on the Transformer Neutral, which was repaired: voltage back to nominal.

    Opened up the welder and inspected for any apparent damage. Nothing but a little dust.
    Checked continuity through the Switch and C/B. Fine.
    Checked Voltage to the PCB. Line voltage at PCB. Fine.
    Nothing burnt. Nothing Cracked. No discoloration.

    Could i get some input on process of trouble shooting from this point.

    Does the welder require a signal from the fan Motor prior to powering on?

    I have yet to do a any tear down until i can get some feedback on possible simple solutions of troubleshooting!
    Last edited by Dread; 09-17-2020, 04:09 AM.

  • #2
    Sounds like something in the main board is saturating after start up. Not much to that machine but one main board. If you have power going into then 99% of the time it's the board.


    • #3
      Is there a self check pre-power?, such as verification of fan operation/sensor?

      There doesnt seen to be any apparent damage to the PCB, unless it is a sub-component, which i feel like could be repaired if i had a schematic...but i'm pretty sure capitalism will not allow the sharing of the PCB schematic.

      I have yet to hear back from Miller tech for a schematic in 2 weeks since i contacted them.

      I guess i will have TO DO IT THE HARD WAY.... and trace everything out!

      Good grief!


      • #4
        Dread, I have not seen the inside of the newer inverter smaller millermatics like yours, but looking through the owners manual, it appears to have a power factor boost circuit before the DC bus (the one inductor). It also looks like there is no auxiliary transformer for the control circuits, so it probably has an onboard switch mode power supply (at least one). What diagnostic tools do you have? How far into the machine have you traced the power? How do all of the heatsinked components on the board look? Can you post pictures?


        • #5
          All i have is a multi-meter.
          I have not done anything yet, as one of my probes were broken and waiting on delivery.
          I will post some pictures in the next 24 hours


          • #6
            If you are looking for a specific angle of component let me know?


            • #7
              Dread, you can do quite a bit with a multimeter and the power off. In your pictures, the line input to the board in the upper middle, the component to the right is the bypass relay, then what looks to be the underside of the bridge rectifier. What resistance do you have between the violet connector and the lower left input to the bridge rectifier? It should be the value of your pre-charge resistor. Do a diode test across your bridge rectifier, both directions. The left side are the AC inputs, the right side are the DC outputs. The (-) output should go to the (-) DC capacitor bus and the rectifier (+) should go to one of the orange leads (the orange leads go to your boost inductor for your PFC Boost converter). The other orange lead should go to a diode, which is then connected to the (+) DC capacitor bus. It looks to me the onboard power supply is powered by the DC bus and isolated by the transformer in the middle of the board. It provides power to the output and what looks to be the controllers (bottom middle, left) as well.
              A bit more dangerous, particularly with the voltage and the potential for fragments from failed/exploded components. With all of that out of the way, you can check AC to the input bridge rectifier, then DC out of the bridge rectifier to make sure you're getting ~340V there. If so, check the (-) output of the bridge rectifier to the forward diode connected to the orange lead. I don't know how high the bus voltage is on that machine, so please be careful. It could be anywhere from ~390V DC to much higher, but it is definitely higher than 340V.


              • #8
                Ok give me some time to get back to you on my progress.

                Out town at the moment.

                Thanks for some direction


                • #9
                  I identified the PCB Bridge rectifier supposedly/hopefully and qualified that in the picture: voltage reading 0.682 mOhms

                  The Diode read 0.590v and Infinite/O.L.
                  Last edited by Dread; 10-02-2020, 05:43 PM.


                  • #10
                    Dread, that is not the bridge rectifier. The bridge rectifier looks to be on the underside of that board, to the upper right of the input relay (black plastic box with "Omron" written on it) That component looks to be the transistor for the auxillary/isolated power supply for the board.


                    • #11
                      Click image for larger version

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                      I thought it was a mosfet. patience Please, thank you.

                      The bridge rectifier i found from the manual part ... have not accessed it yet...looks to be only a heat sink from the vent side

                      >>>>electrician<<<< not electronics

                      Click image for larger version

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                      Last edited by Dread; 10-02-2020, 06:41 PM.


                      • #12


                        • #13


                          • #14
                            Heres what the manual gives you.
                            Attached Files


                            • #15
                              Dread, what is written on the top two transistors (red dot)?