A Shorted wirewound resistor?

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  • socketa
    Asbelowsoabove
    • Jun 2014
    • 658
    • samsara
    #1

    A Shorted wirewound resistor?

    This resistor is from an ATX APFC PSU that connects bridge rectifier negative to primary capacitor negative
    I think that it's a current sensing resistor for the APFC
    Is it correct that it's color code indicates that it should be 0.47 ohms?
    I measured it to be around 0.08 oms
    The PSU blew up (visible arc flash) after problems with a powerstrip, but i got it working now after replacing the 10A fuse, rectifier, etc and removing/shorting the APFC diode locations and using a jumper in place of this PFC current sensing resistor
    I don't think that APFC likes being connected to powerstrips, as this is not the first time that i've come across this.
    Has anyone else come across a wirewound resistor that failed short instead of open?



    For the sake of completeness i attached extra photos of:
    the pink primary current sensing resistor, which tests in spec despite the wire being exposed (due to overheating?),
    and the small chopper transformer that had a piece of the top blown off (i stuck it back on with epoxy)
    Attached Files
    Tags: None
    • CapLeaker
      Leaking Member
      • Dec 2014
      • 7976
      • Canada
      #2
      Re: A Shorted wirewound resistor?

      that's fine... you need a real good calibrated DMM and test leads to be that exact.

        Comment

        • stj
          Great Sage 齊天大聖
          • Dec 2009
          • 30919
          • Albion
          #3
          Re: A Shorted wirewound resistor?

          thats a fuseable resistor, if it's not open circuit then it's fine

            Comment

            • socketa
              Asbelowsoabove
              • Jun 2014
              • 658
              • samsara
              #4
              Re: A Shorted wirewound resistor?

              OK thanks
              i used a new aneng meter to check it
              and just out of interest ordered some new 0.15 ohm fuses, to check the meter against,
              and will post back here, if they arrive, to confirm if it does indeed have a lower resistance.
              Anyway, according to a schematic that i found, it looks to be a current sensing resistor for the APFC - so if the resistance varies too much from 0.47 ohms, then wouldn't that upset the APFC, and not be OK?
              Last edited by socketa; 05-17-2022, 01:56 AM.

                Comment

                • stj
                  Great Sage 齊天大聖
                  • Dec 2009
                  • 30919
                  • Albion
                  #5
                  Re: A Shorted wirewound resistor?

                  thats too high for current sense i think - more likely it's inline with the gate of the fet

                    Comment

                    • CapLeaker
                      Leaking Member
                      • Dec 2014
                      • 7976
                      • Canada
                      #6
                      Re: A Shorted wirewound resistor?

                      Before you go too crazy with this, you also have to understand the tolerances on the resistor and the tolerances on your new DMM.

                        Comment

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