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Miller board help please

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  • #61
    I haven't had the best of success helping folks with board troubleshooting, but hopefully this will work. That thermistor is there for inrush current limiting. That's why it is in parallel with the relay right next to it. It controls the current through the rectifier (bottom right under the heatsink) which rectifies the voltage that charges those two big capacitors. Once those capacitors are charged (or after some period of time), the board logic engages the relay, which bypasses the inrush limit thermistor. That's why the board didn't work at all when one leg was disconnected. If the machine powers up and you're getting lights, that thermistor is probably doing it's job.

    That buzzing noise you hear is common, and that actually looks like the same buck circuit used on a Miller Dynasty/Maxstar 200 (that big round component in the center is the inductor for the buck circuit). It buzzes on the Dynasty 200 too. I'll work through the pictures you posted to see if I can help. If it's compressor overcurrent, there's probably a big resistor (or two) in line with the power to the compressor that acts like a shunt to sense current. The shunt may be open or the logic circuit for the shunt may have issues. Can you work your way back on the board from the negative power lead to the compressor?
    Last edited by jjohn76; 02-03-2020, 09:21 AM.

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    • #62
      Looking more at the board, your compressor circuit looks like it's on the left, just above the left transformer (bottom left corner). It's powered by some type of forward converter through that transformer with the output rectifier on the heatsink and the inductor just above it part of the output filter. That logic circuit in the upper left is what's triggering those LEDs. What connects to the connector on the far left, 2/3 of the way up?
      Click image for larger version

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      • #63
        I will post more pictures, thank you so much for taking the time to help diagnose the problem

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        • #64

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          • #65

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            • #66
              Back
              Attached Files

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              • #67
                What have you measured on the board so far?

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                • #68
                  Sorry but nothing because i ask customer service for help to give me some direction on what to measure but I didn’t get no answer

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                  • #69
                    Ok, do you have a multimeter, preferably with a diode tester? If so, please measure the resistance across the compressor connector sockets. With the diode tester, check the two outside pins with the middle pin on the rectifier on that lower right heatsink.

                    Also, what are the labels on the white chips (optocouplers?), as well as that little 8 pin black chip to the right of the heatsink?
                    Last edited by jjohn76; 02-06-2020, 11:59 PM.

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                    • #70
                      Hi JJohn76 sorry for the delay lots of things happen I will try and get a multimeter right now i don’t have tools, here are the pictures
                      Attached Files
                      Last edited by Agguilar; 01-14-2021, 10:21 PM.

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                      • #71
                        Hi Aguilar. It's going to take me some time to dig back through what we discussed and were trying to fix, but will get back to you when I get a chance to go through the thread.
                        Jon

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                        • #72
                          Originally posted by jjohn76 View Post
                          Hi Aguilar. It's going to take me some time to dig back through what we discussed and were trying to fix, but will get back to you when I get a chance to go through the thread.
                          Jon
                          Thanks !

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                          • #73
                            Click image for larger version

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ID:	613167 Here’s a diagnostic tool to start you in the correct direction
                            Attached Files

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                            • #74
                              Thanks Welder dr

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                              • #75
                                I have the same issue with a hobart 250ci. powers on, green light, led 26 is green, led 25 and 30 flash when the trigger is pulled. I get the same small spark when put against a grounded piece of metal. Resistance across the compressor power terminal is near zero. I traced back to the part on the left with the heat sink, it is labeled as a diode but looks more like a MOSFET. p/n is 63CPT100, after searching for the part is a common cathode diode array, basically two diodes with common cathode. It is commonly used for power rectification. Diode check shows near zero volts. I think this might be the blown part. Which makes sense if it is sorting out the transformer and tripping the relay for overload protection. They do not make these anymore, or the listed replacement V60100PW-M3. A common theme with the failure of the plasma cutter is that they have sat for a few months or longer and then do not work. I wonder if it is due to this diode array absorbing water and shorting out which might be why they are no longer made. If found a replacement part MBR60100PT and have ordered it. I am going to remove the part and verify the diode test out of the unit to be sure. I will keep you posted.
                                Last edited by silocrash; 02-23-2021, 11:29 AM.

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