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Need help with AMT304

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  • Need help with AMT304

    Your help would be much appreciated. I bought the xmt304 two years ago and using it to feed a Miller extreme wire feeder. The symptoms now are, 1. The voltage flips from the set voltage to 7 about every 2 seconds 2 in stick mode the amps is wide open. I can put a jumper wire between terminal A and B on the 14 pin and it will weld in the constant current position. I spent some time with Miller support and determined that the problem was in the control board. Buying a new board is out of the question for 2 reasons 1. I am 82 and live on a very small fixed income. 2. I am from the old school and do not like the idea of scrapping a thousand dollar board when a 5 dollar part would fix it. Once again, thanks for your help.

  • #2
    Some you can fix, some cant. Schematics are often hard to come by, i have a tv reairman bud fix some

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    • #3
      What year is your machine (or what are the first three digits of your serial number)? Have you tested it in all functions (VS, Lift Start Tig, CC Tig, Stick)? It sounds to me like an issue either in the signals from the front board or signal issues on the main board. It almost sounds like your current sense circuit isn't working right.

      I didn't understand the voltage flipping part in stick mode you mentioned above - please confirm if this was in stick mode or VS mode. It sounds like you were in VS mode if you were setting voltage for an Extreme.

      The boards start to act erratic when the filter caps on the boards start to go, especially on less than clean power. On one XMT 304, I could only get some symptoms to show on a friend's farm, so to show on my garage shop power, and watch the issues disappear on an industrial shop's power.

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      • #4
        Since when is this a WELDING forum? I thought it was TackIt's "copy and paste every last chain email you receive" forum!

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        • #5
          Originally posted by Helios View Post
          Since when is this a WELDING forum? I thought it was TackIt's "copy and paste every last chain email you receive" forum!
          Lol i think Tackit got BANNED.

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          • #6
            Thanks for your help and quick response.
            The serial number is LB186315.
            The voltage flipping occurs in both stick and VS.
            I have done a visual inspection of board with close attention to the Caps. I am using the same power source for years. I forgot to mention that when connected to the wire feeder I hear a clicking sound of maybe a relay that is sync with the flipping.
            Thanks again

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            • #7
              tackit finally got banned? That took about a month longer than it should have. I was worried no one was going to do anything and he was going to be allowed to run the forums into the ground.

              How hot are your voltage regulators after the unit has been on a couple minutes? They're the two big heatsinks on the top board.

              Try unplugging the hall effect sensor on the positive output connector.

              The only relay is the precharge scr trigger relay, that I can think of at least. I haven't done much welder repair lately - will check the schematics when I have more time.

              Most board-level repairs will require a good multimeter, possibly an oscilloscope, a commitment to safety, and some electronics know-how. Do you have these?

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              • #8
                Thanks for helping me with this project.
                I am not a electronic technician but have some experience with circuit boards. I held a general class Ham license (K5CMF. Assemble my gear ( transmitter) from Heath kits, you are probably too young to remember Heath kits. A few weeks ago I installed a capacitor kit in my LG tv. I believe with your expertise and guidance we could make it work.
                I have a multi meter ( Fluke) but not a scope but could borrow one.

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                • #9
                  I’m just a tech class (KC5HOZ), but I haven’t been active for years. My first transmitter and receiver were Heath Kits I found, brand new in the box, at a garage sale. Picked up a code practice box and a 2kw linear too, got to build them all. I loved that linear amp, two monster tubes in the middle, very positive “click” and “hum” when you turned it on. She had a warm up a minute. I’ve been thinking about getting involved again. The little I learned way back then has helped me with many things as I’ve been on my travels.

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                  • #10
                    As I said, you also need to pay attention to safety working on these. In addition to mains voltage while you have it plugged in, the big capacitors can store a lethal charge for some time after the unit is unplugged. Any power-off testing that involves the power board or that side of the machine in general needs to be preceded by verifying with a multimeter that both capacitors are discharged to a safe voltage. And, no, don't discharge them with a screwdriver - it's bad for the capacitors, potentially bad for the IGBTs, and you'll need a new screwdriver.

                    The first thing I'd check is the + and - 15V supplies. You can measure both of them on the hall effect sensor connector. The temperature of the two voltage regulator heatsinks can also point to something dragging one of them down, which causes all sorts of problems. Since you have an issue related to current control, I'd also try unplugging the hall effect sensor and seeing what changes, and measuring its output and confirming it's correct, at 0v with no weld current.

                    Edit: If you haven't done so yet, you might want to run through the pre-power checklist. Since you can weld at full power, I'm not expecting it to find anything, but it's worth a check.
                    Last edited by Bushytails; 09-15-2021, 08:34 PM.

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                    • #11
                      Thanks for your information and concerns about the safety issues with capacitors, I have worked with them when I worked in industrial maintenance. They are like electric fences, I learned too respect very quickly.
                      I spent over a hour with a technician at Miller support, with the unit powered up we checked voltage at maybe 20 locations . He said all seem okay in main areas. He had me put a jumper wire between the A n B terminal on the 14 connector and see if it would weld okay in the CC position. It did. He said that confirmed that the problem was in the control board .

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                      • #12
                        Goodness....how much is a new control board?

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                        • #13
                          P/n 240570 $ 1470.74

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                          • #14
                            That dollar number says it all.

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                            • #15
                              Yikes.

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