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  1. #1
    Join Date
    Jul 2004
    Posts
    23

    Default Need help bad 351 died

    Hey guys I recently purchased a used 351 machine very clean and nice was working great yesterday I went into the shop and it tripped my breaker on dcr and dcs the ac works ok.Well I blew it out looking for something obvious but don`t see any sign of arching but it trips the breaker in dcr and dcs.I`m an electrician by trade so I`m guessing since it trips only on dc its a scr or rectifier somewhere does anyone here know how to dianose such a problem? I`m only hobby welding so this isn`t a weld shop where I can afford a costly repair.My plant where I work offer this for aution and thats how I got such a big machine, IF I can`t fix it I`d be interested in a swap for a smaller welder.

  2. #2
    Join Date
    Oct 2007
    Location
    Medina, Wisconsin
    Posts
    103

    Default

    Check the D1 diode on the main rectifier. My guess is that its shorted. Unhook the welding cable from the D1 and put polarity switch inbetween positions, then check with ohm meter. It should be open in one direction and closed in the other, if not its junk.

  3. #3
    Join Date
    Jul 2004
    Posts
    23

    Default

    Thank you for your assistance. D1 is that the one with big bolt and nut.Not the ones sandwiched between the cooling plates correct?I`ll refer to my manual.Thanks again. Man my heart sank when it quit. I`ll post back tomorrow with the news.

  4. #4
    Join Date
    Oct 2004
    Location
    Edmonton, Alberta
    Posts
    7,669

    Default

    D1 looks like a regular diode with a pigtail on it, the ones sandwiched between the plates are SCR's.

    Disconnect the pig tail before you test it, perferably with a diode tester

  5. #5
    Join Date
    Jul 2004
    Posts
    23

    Default

    Thanks as soon as I get home I`ll get it out and check it.

  6. #6

    Default

    Sounds exactly like the D1 issue. D1 is a flyback diode used only in DC and it's purpose os to protect the main rectifier from the stabilizer when the arc is shut off. To test properly, disconnect one side of the diode out of the circuit.

    Good luck
    Andy

  7. #7
    Join Date
    Mar 2008
    Location
    Dallas,Tx
    Posts
    172

    Default Syncrowave 351

    If that is your only problem, those diodes are cheap. You can pick one up for around 20.00. weldersales

  8. #8
    Join Date
    Jul 2004
    Posts
    23

    Default

    Well the D1 is bad shorted. OK is there a root cause I should be looking into vs just replacing it. And also can someone send me the info Can`t beleive 20.00 part. Its a 037-956B looks like 275Amps 300v Made in mexico.Please send me info for a replacement Thanks in advance,You guys are ok with me nomatter what the lincoln boys say

  9. #9
    Join Date
    Oct 2004
    Location
    Edmonton, Alberta
    Posts
    7,669

    Default

    Quote Originally Posted by Reel-Break View Post
    Well the D1 is bad shorted. OK is there a root cause I should be looking into vs just replacing it. And also can someone send me the info Can`t beleive 20.00 part. Its a 037-956B looks like 275Amps 300v Made in mexico.Please send me info for a replacement Thanks in advance,You guys are ok with me nomatter what the lincoln boys say
    List price from Miller is $62, If your LWS doesn't have a repair shop, the price for this part may be somewhat higher

    This is also a common part on Ebay, I bought a bunch of new ones for like $5 each

  10. #10
    Join Date
    Jul 2004
    Posts
    23

    Default

    ok replaced the diode that was shorted still trips as soon as I turn machine on dcs or dcr I removed the scrs and none are shorted 1,2,3,4 Can someone share some troubleshooting info. Thanks

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