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SA 250 will not strike an arc

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  • SA 250 will not strike an arc

    My Lincoln SA 250 will no longer generate enough current to strike and arc. All it puts out is little sparks. The funny thing is if I turn the "Fine Current Adjustment" all the way to 100 it will pop an arc briefly. This seems to work no matter where I have the main "Current Adjustment" set and if I turn the fine current to anything but 100 it will not arc.

    I am not sure where to start here. I just put all new brushes on this thing. Anything I can check? Where do you check the exciter output?

    I am not real clear on the path things follow. What direction does power flow through one of these things from the generator to the rheostat to the leads or what?

  • #2
    Make sure you're not in "Remote". Make sure your leads are ok, ie, see if the leads yank out of the connectors. If your getting a spark and the above is ok. I'd imagine that you're lost your control rheostat.

    Do you have auxillary power??

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    • #3
      Thanks for the reply ventureline. I checked everything you suggested. I do not have remote. The leads are all in good shape, tight from end to end. Yea, my auxillary power seems to be working ok.

      Is there a resistance check I can do on the rheostat? I hooked my ohmmeter up to the fine current adjustment, one on each end of the circle where there is a wire connected it reads 0 resistance...

      Would having the fine current adjustment go bad prevent me from welding if the main current adjustment was good? If so, is there a way I can jumper this to see if it is the problem? Thanks!

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      • #4
        Check your main rheostat. I had one on a SAM 400 that came loose and broke one connection and the machine did just what you are talking about

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        • #5
          If you have auxillary, the exciter, and control fuse are ok, so your missing your field which hopefully is a failed rheostat, the rheostat should measure in at 64 ohms or within 10%. If it's open, ie, 1meg. there's your problem, otherwise you may have major problems.

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          • #6
            Try pulling the exciter brushes up while the machine is running.... If that dont work you can "flash" the fields.. Otherwise it'a probably your exciter armature I just went through that not too long ago with my SA-200...........

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            • #7
              Try this.....

              Check the exciter diode in the main generator housing. White wire from the exciter brush holder to the main gen section. If ok find the the 2 wires that go into the top of main gen sec(blue and red). Find a open area to cut( you can splice back if ok) Check the wire going in to the main gen....50ohms. If not your feild coils are bad. There is a chance that the brushes are not making good contac. Free up and clean slip rings and armuture. Good luck!

              frank
              XMT 300CC/CV (yes it still works)
              Bobcat 225, Hobart Hefty CC/CV wire feeder, Profax spool gun,Victor & Smith O/A, Lincoln Tombstone(sold), Airco HF box (old Miller) MM175, IR 4KW gen set,all paid for, all work. My newest addition MM130 salvaged from a Kitrina flood area. Cleaned up and works great. . Just added a Miller Thunderbolt AC/DC, total cost to repair both less than $200.00, they both work great...another Katrina cast off.

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              • #8
                Originally posted by snowjoker
                Try pulling the exciter brushes up while the machine is running.... If that dont work you can "flash" the fields.. Otherwise it'a probably your exciter armature I just went through that not too long ago with my SA-200...........
                His exciter works, as he has auxillary power. flashing the fields in this unit will take out the exciter diode locater in the genertor housing.

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                • #9
                  Thanks for all the help folks! Turns out a couple of windings on the rheostat were broke. Gonna replace it this weekend and let you know what happens. They look like they got burned... what would cause this?

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                  • #10
                    Probably old age and dirt.

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                    • #11
                      The rheostat was fried. Also the two wires going into the top of the main generator (I believe they are red and blue) are broke and shorted. I think these are the ones you are talking about frank. Gonna patch them up and hopefully that fixes my problem. Also, I am having trouble locating the diode. Can someone tell me where I can find it? Thanks for the help!

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                      • #12
                        Replace the rheostat (64 ohm 150 watt) run up the welder. If all works then the exciter diode is ok, if no auxillary (first clue) then the exciter diode, or control fuse and/or control bridge may be fried.

                        You'll find it under the generator cover 1 a clock position looking at the face of the welder.

                        Check it with a diode checker. Now if you have auxillary power but no weld power, I'd be looking at a popped field coil $1000 fix

                        Another reason for a smoked rheostat, is a failed contol bridge, ie, rheostats don't like AC power, they become smoke shows..This unit resides near the control fuse (which may be blown) back right side of front panel about middle.

                        Hello from Thailand...

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                        • #13
                          I believe my problem is the two wires running into the top of the generator. One of them is broken and the other stripped down to the bare wire. These are the only two wires running into the top of the generator besides the heavy guage wires that run to the lead block. I can reach in and feel where one of them goes but the other I cannot find and I think I am going to have to pull this thing all the way apart to patch the wire back together. I know my description is a little vague but can someone tell me where these two small wires run to. My wire diagram with the manual doesn't seem to be much help. Thanks.

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                          • #14
                            # "N" & # "U" wires, run to your eciter diode, control bridge, & control rheostat. Take an Ohm meter and check the resistance of these two wires going into the generator. Should be a closed circuit, ie, less than 2 ohms.

                            Fastest time I've stripped a generator down is 2 .5 hrs, but thats with an overhead crane, the right pullers, air tools, and having pulled apart over a hundred previously. If you attempt to pull it apart, you'll want to contact me directly
                            ventureline@shaw.ca
                            Last edited by ventureline; 06-01-2006, 09:05 AM.

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                            • #15
                              Follow up on no arc

                              I'm a relative newbie here. Haven't welded since high school (15 years ago). I just got my newly acquired SA200 started after it was siiting outside for 11 years. I changed the oil & filter, cleaned air filter and flushed the gas tank / line. I replaced the stinger and the clamp and reset the lead connections back at the machine. It seems to run fine but doesn't always strike an arc. I'm experimenting with 6011 and 6013 rods and some different scrap metal that I have. It too seems to strike better with the fine curent cranked up, regardless of the main current setting. Is there a source of maintenance or troubleshooting books available for this unit? Any direction would be appreciated.

                              Thanks!
                              Kevin

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