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  • Miller board help please

    hi all I’m new here I will like to fix my machine that uses a miller board I’m looking every were to see if I can fix it and not just replace the board, that that’s the solution from customer service,

  • #2
    Welcome to the forum!

    The first step would be to tell us what kind of machine, the serial number, symptoms of the problem, what board they told you needs to be replaced, and any other info like how old is the machine, how much use does it have, what is your level of experience with electrical troubleshooting, what electronic test equipment like a digital multimeter do you have, and anything else that will help the people here to help you. There are lots of people here who will try to help.

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    • #3
      Thanks, the other information did not post , the machine is a Hobart 250ci it haves a miller board I have all tools needed to fix electronic like meter, soldering iron etc the machine is old but look brand new

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      • #4

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        • #5
          Symptoms: power on, power light comes on as well as the "trouble" light, the fan spins up. The built-in compressor does not come on. I have verified that the compressor itself works by supplying 12v to it. It seems to be in shutdown mode, which can be from overheating, improper supply voltage, or shield cup is not in place. When I squeeze the trigger, I get nothing- no relay click or anything.

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          • #6
            I don't see a light labeled "trouble" in the manual. Is the light that's on Power, Cup, or Temp? Is more than one light on? Are they flashing or steady? Assume you've been through the troubleshooting chart in section 6-6 of the manual?

            Have you checked with an ohmmeter the wires from the torch where they plug into the circuit board? Unit unplugged from wall power, check open/close of contacts for both the trigger and the cup switch where the wires enter the circuit board. If you need "how to" to do that, let us know.

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            • #7
              It’s the power and temp light that flashes when trigger is press it flashes like 15 times both, yes I have checked the torch cables and all tested good trigger, cup cup sensors and torch

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              • #8
                Yes I have the manual this is from page 21 of the manual : “ Power/Temp Lights
                When both lights flash, the com- pressor current limit was exceeded either above or below its operating range. The lights flash for 15 sec- onds before the torch can be retrig- gered. If this condition continues during unit operation, have a facto- ry authorized service agent check unit.”

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                • #9
                  This is the same problem I'm having? The video is not mine but same problem: https://youtu.be/aYG95nGalYU

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                  • #10
                    https://forum.millerwelds.com/forum/...-plasma-cutter

                    I wonder why some win the lotto and not me. Then I remember... I didn't buy a ticket. I watched the video and read the comments. Lol. I like the one where the fellow said it saved him from opening his up. Priceless. Getting your hands dirty is kind of like buying that lotto ticket. You won't be a winner if you don't.

                    I'm buying an old van tomorrow. Because of that, I watched a video of buddy checking the EFI fuel pump in his truck. When he could start it, it ran like crap, unlike your PAC not at all. But that's not the point. The point is it pumped fuel but didn't build enough pressure. Anyways, being systematic is part of the trouble shooting process. Learning how things work and possibly function part of that process. Sometimes you have to get your hands dirty because there are no easy answers.

                    Once again I'm speaking in babble. Not answering the question of why, but moving lips with a bunch of gibberish. All those people with the same problem, kind of makes you want to be the guy who solves it don't you think? Buy the ticket, you can be that guy.

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                    • #11
                      Thanks Noel you help a lot

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                      • #12
                        Just to let you know I already dismantle the machine I like to search and not afraid of open electronics, I posted the video because I didn't record the problem I was having with the machine, I have a lot of pictures that I took of the board and inside the machine, I completely disassembled, and assembled every part, including the torch to see any burn part or something that will indicate a problem

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                        • #13

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                          • #14

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                            • #15
                              Based on the info on page 22 of the book, it appears whatever checks the compressor current has failed and is tripping the protection circuits. Also possible there is something with the compressor itself that is causing it to draw too much current and causing the fault, but it might still work OK with an externally provided power supply. Could be a hall effect device doing the sensing, but I would guess it's more likely just a transistor circuit that senses voltage drop across a very small series resistor--probably cheaper to make. Unless you are pretty knowledgeable of component-level circuit board designs (to try to figure out how the circuit works without a schematic) and troubleshooting, I think you are skunked here. Alternatively, if you are good with soldering circuit boards, you could start checking components in the compressor current sense portion of the board one at a time. Since this is all surface mount technology, you are going to need a hot air soldering system. If you find a bad transistor, don't stop there--try to figure out what might have caused it to fail. Could be long and laborious. Considering that this seems to be a common problem, I would guess there is a design issue here that needs to be resolved. If you happen to have access to an infrared camera (perhaps not likely, but possible), you could try a photo of the board while you have it running and pulling the trigger, and see if anything looks hot in that area of the board. You could also try an infrared thermometer, but they are pretty broad in coverage to look for specific hot spots; might be worth a try, though.

                              Looking at the pic of the board, I don't see many discrete components--mostly surface mount ICs. Makes it even more difficult to troubleshoot without a schematic. In fact, boards nowadays are pretty much designed to be trashed when they go bad. Very frustrating for a cheap old-timer like me, but as my wife used to say, "You're just going to have to deal with the fact that it isn't 1970 any more!"
                              Last edited by Aeronca41; 08-09-2019, 10:50 AM.

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