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Thread: Miller Dynasty 300 DX repair- summary/consensus?

  1. #1
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    Apr 2010
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    Miller Dynasty 300 DX repair- summary/consensus?

    Miller WWWeb Readers/posters;

    DO I correctly understand that the consensus of experience and opinion is that a Dynasty 300 DX with a likely PC-3 board FAILURE is a "boat anchor" and not repairable?

    The unit will weld in stick/output, and displays in TIG Remote Mode, but will not strike an arc in AC (HiFreq) TIG, regardless of pulse settings on or off.

    I've read this board's history as far back as the threads seem to go? and the Miller Weld's forum on the same subject. Then hunted down and read several other forum's where this topic was returned in a Search.

    I don't want to ask for time to discuss, just the sense of the Board's posters- which I understand to be in the negative: this power supply from about 2003-4 vintage is now toast- or maybe a stick buzz box?

    thanks for anyone taking time to confirm or deny my conclusions?

    Cheers,
    Kevin Morin
    Kenai, AK
    Last edited by Kevin Morin; 11-30-2019 at 05:59 PM. Reason: forgot board "Failure"

  2. #2
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    Re: Miller Dynasty 300 DX repair- summary/consensus?

    I would PM Terry (shovelon). Hes had a couple of those repaired.
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  3. #3
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    Re: Miller Dynasty 300 DX repair- summary/consensus?

    Thanks, Soutthpaw, will do.

  4. #4
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    Re: Miller Dynasty 300 DX repair- summary/consensus?

    I believe I have the same issues with my 300DX. Were you able to get the board repaired?

  5. #5
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    Re: Miller Dynasty 300 DX repair- summary/consensus?

    You can repair it yourself for about $500 but you need a little circuit board level knowledge and midlevel/advanced knowledge of electronics .

    1. You must know how to solider very well and be able to take components off of the pcboard with damaging it.
    2. You must know how to check all required components resistors and diodes and transistors you dont have to check the optos.
    3. You have to replace the 2 IGBT modules on connected to PC3 the best place to get those are China they are marketed under the Mitsubishi and they are SanRex in the USA. From China they will be like $100-150 each (This is a normal IGBT that they use in VFD's) The part number must match 100% you cannot use any variant.
    4. You must check ALL of the filters and components on the PC3 most of all the zener diodes. PC3 is mostly a filter board for the transistors.
    5. It WILL burn the optocouplers drivers on pc1 50% of the time. They drive the IGBT's on pc3 you must replace them all if 1 is bad (This is a special type of Opto-Driver for the IGBT gates it is not a normal opto). The optocouplers are white and right beside the plug that goes to pc3 you must check the resistors and diodes beside them.

    This is no easy repair and I realize this is too advanced for most DIY people and most welder repair shops but I thought I would put it out there because Miller no longer makes parts for this machine anymore.
    Also this may not be the only problem with your machine.
    If you dont understand any of this dont attempt the repair.
    Last edited by Diode; 03-31-2021 at 08:57 AM.

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