Nexus NXT250DC

  1. Gino*123 New Member

    Messages:
    7
    Location:
    London
    I have a Nexus NXT200DC that is faulty and I would like to repair this unit. If anyone has the chematics of this welder, I'd like to send them to me.
    Thank you.
     
  2. 500e

    500e Always buy fire insurance a flood is hard to start

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    SWest UK
  3. Gazello Member

    Messages:
    109
    Location:
    Bavaria
    Its a migatronic Derivat, pi 200dc probalby
     
  4. Gino*123 New Member

    Messages:
    7
    Location:
    London
    Hello,
    I saw that manual but my unit is NXT250DC, not NXT250AC/DC like in manual from link above.
    On the other hand, looking on manual above, I saw that my unit doesn't have all boards that can be seen in page 16 of 18 from this manual.
    Regarding the faulty of my unit, if I can't find the schematics, maybe someone can tell me what deffect has encountered and the solution for remedy. In this way maybe I can solv the faulty of my unit.
    Thank you.
     
  5. Gino*123 New Member

    Messages:
    7
    Location:
    London
    Sorry for the name of the topic. This should be Nexus NXT250DC.
     
  6. Gino*123 New Member

    Messages:
    7
    Location:
    London
    Hello,
    In picture below is the board of NXT250DC. Maybe someone can help me:
    NXT250DC.jpg

    - what capacitors are fitted by manufacturer (see picture, upper area)
    - what are the missing parts ( bottom area of the picture)
    Thank you for the help.
     
  7. Seadog

    Seadog Forum Supporter

    Messages:
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    Location:
    NE London - UK
    Don't assume that because the components are not fitted that they should be. Variants of a machine often have subtle differences in the circuitry. (Unless you know for a fact they they have been removed by someone)

    If you look at the soldered connections just below the two grey capacitors marked with a "J," there are some very suspect looking joints. In fact, the two to the left of the spacer don't seem to have any solder on them.

    All of the information on the capacitors should be visible on the printing.
     
    DavidL likes this.
  8. Gino*123 New Member

    Messages:
    7
    Location:
    London
    Hello,
    The two big black capacitors are touching the cover of the unit and I assume that this component aren't the right height. Maybe the previous owner has replaced them with others one without tacking into account the max height of the capacitor and maybe the value also.
    The second area marched with red (missing parts - bottom area of the picture): it is visible that the soldering gun was used.
    Regarding your remark, you are right: in that area are the two IGBTs that need to be replaced and desoldering is in progres.
     
  9. eddie49 Member

    The smoothing capacitor(s) after full-wave rectification of the AC mains is/are typically from 500 to 1000uF and 400 to 500v. I think that the ones mounted on your PCB are 680uF 400v, and this is a very common value. I am sure they are correct for your unit. If they had been replaced, you would probably be able to see that the solder was disturbed. Note that the correct voltage across these two capacitors should be about 325v DC.
    The two PCB tracks at the location where you think a part is missing have both SMD pads and plated-through-holes. Similar tracks are seen in a few other locations, and are used to mount what I believe are tantalum bead capacitors.
    I think it would be helpful if you tell us what is the defect on your unit.
     
  10. tflnemesis

    tflnemesis Member

    Messages:
    559
    United Kingdom
    From the picture it looks to me that there are 2 components that have broken away from the board on one side.
    The components I am looking at are the 2 grey disc like things just to the left of the marked capacitors, one is clearly broken on one side and the other looks like it might be broken but isn't as clear.

    *edit*

    After a closer look they may be soldered on the underside through the gaps.
     
  11. Gino*123 New Member

    Messages:
    7
    Location:
    London
    The two capacitors are indeed 680uF/400v and, ofcourse, the solder was disturbed which means that this two ware changed. Also the position of the two green rezistor is "unnatural". Any way, I will change the position of this two parts after I check them.
    The second area (with missing parts) also has solder disturbed and I hope to find what was there (maybe someone can check on his board).
    So far I find that the two full bridge IGBT, 20MT120UF, are damaged (one has been smoked).
    Regarding the two components that are close to the capacitor, left side, this two parts are ok.
     
  12. Seadog

    Seadog Forum Supporter

    Messages:
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    Location:
    NE London - UK

    They're known are varistors or VDRs and limit surge.
     
  13. Shox Dr

    Shox Dr Chief Engineer to Carlos Fandango

    Messages:
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    Location:
    East Yorkshire
    I cant help you with your problem. But know its worth fixing. Those sets can take some beating. I lost count how many times the lad next to me would pull it off the bench eith the leads. Never missed a beat.
     
  14. Gino*123 New Member

    Messages:
    7
    Location:
    London
    No one has a NXT250DC to help me to find what was in area where I put "missing parts"?
    I checked all the diodes and transistors and there is no sort circuit, so I guess they are ok.
    The next step is to check the four circuits that generate the signal for the IGBTs (with an oscilloscope).
    I will come back with the results. But until then, please help me find out what's with the area mentioned above. Thank you.
     
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