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  • 251 wire feeder

    Hello I'm new to this and I bought a millermatic 251 not running put a power cord on it and the fan comes on and I get a hot smell where do I start the diagnosis thank you

  • #2
    Fan comes on as soon as I flip the switch nothing else

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    • #3
      Model NUMBER
      Serial NUMBER
      Made by "Miller Electric"
      or Miller?

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      • #4
        Serial number LC620568
        millermatic 251

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        • #5
          Open it up and look for something getting hot.

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          • #6
            Try opening up welder and use a digital temperature gun to scan the boards and wires to find out where the unwanted heat is coming from.

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            • #7
              I can't say I remember my 2003 model 251 fan staying on all the time.

              https://forum.millerwelds.com/forum/...-fan-on-demand

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              • #8
                Originally posted by tackit View Post
                I can't say I remember my 2003 model 251 fan staying on all the time.

                https://forum.millerwelds.com/forum/...-fan-on-demand
                You are prob right.
                Bob Wright

                Spool Gun conversion. How To Do It. Below.
                http://www.millerwelds.com/resources...php?albumid=48

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                • #9
                  I've opened it up and and done slot of looking on the internet. I think I found the rectifier bad so I have that ordered not sure if that is all that is wrong still going to test other components

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                  • #10
                    I hope you found the problem, many times there is a series of problems which go undetected but are part of the problem.

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                    • #11
                      Finally got back to the 251 put new electronics on the rectifier and had the circuit card rebuilt now seems to work other than no digital readout. Not sure what to check next

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                      • #12
                        Interesting that is. (me...looking at a board) I wonder what that thing does? ( what I'd hope for an answer) "Oh that thing, that's the chip of power that lights the read out on a board"... (me) " Coooool.".

                        You find it do point it out, I'm curious to see what one looks like.

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                        • #13
                          Can you confirm you're getting 35V from your main board PC1 to the meter display board PC2? Unplug RC1 on the display board and check the voltage across pins 1 and 2. Then clean both sides of that lead (all four pins/sockets on both connectors on both the wire and boards, both boards...)

                          Also, can you provide a little more detail on the repairs so far? What electronics on the output rectifier SCRs? What was wrong with the main board and what components were replaced? If the above isn't it, it could be damaged outputs on the main board microcontroller (possible problem and would be impossible to fix without a programmed replacement microcontroller), a problem with the meter board microcontroller (same probability to break and fix as the other microcontroller), it could be a break between the communication lines between both microcontrollers (suspect zener diode, resistors and traces, or the connectors, and I could walk you through this if needed), bad power on the display board (there is a buck converter that takes the 35V down to 5V a component could be bad), or bad power to the display board (not getting the 35V, would need to troubleshoot why).

                          I would attack these in the reverse order listed, which starts with confirming 35V and ensuring there is good, clean, solid contact on both ends of the connection between the two boards.
                          Last edited by jjohn76; 10-22-2019, 08:03 AM.

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                          • #14
                            Thanks jjohn76. I replaced the black box with two electric terminals on the rectifier and sent the main PC board off and got it back with no report on the problems.

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                            • #15
                              Ok, that black box just looks to house the snubber capacitors. Please confirm the 35V is getting to the display board. We can figure out which way to go from there.

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