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.
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Thread: Need help bad 351 died
06-08-2008, 09:29 AM #1
Need help bad 351 died
06-09-2008, 07:30 AM #2
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.
06-09-2008, 09:23 AM #3
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.
06-09-2008, 10:21 AM #4
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
06-09-2008, 10:33 AM #5
Thanks as soon as I get home I`ll get it out and check it.
06-09-2008, 01:05 PM #6
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.
06-09-2008, 02:03 PM #7
If that is your only problem, those diodes are cheap. You can pick one up for around 20.00. weldersales
06-10-2008, 10:53 AM #8
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
06-10-2008, 11:36 AM #9
07-16-2008, 08:19 AM #10
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