Asus switching drop

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  • jasko_jacker
    Badcaps Legend
    • Oct 2014
    • 1137
    • italy

    #1

    Asus switching drop

    I have a asus power supply that with a load , drop from it's nominal voltage to 16 V. I haven"t a schematic so my question is: it makes sense to open it, it's an easy fault to detect ?
  • stj
    Great Sage 齊天大聖
    • Dec 2009
    • 30991
    • Albion

    #2
    Re: Asus switching drop

    the question cant be answered till you open it.
    you may see caps with the tops burst open - easy fix.
    or it may look normal - and take some time.

    Comment

    • jasko_jacker
      Badcaps Legend
      • Oct 2014
      • 1137
      • italy

      #3
      Re: Asus switching drop

      Hi, thanks for replay. I have opened it and I have desolder all six 1000 mF caps in the output stages, no sign of faul externally, I have measured them with a meter and all have the nominal capacity. I read that it's possible that there is a fault even the capacitance is correct and they must be tested with appropriate equipment, it's right ? I have a mega328 component tester and I will try to check them with it to find more data (but this isn't a professional equipment)
      I'm checking all resistor and non electrolitic caps but I don't know if this can help to solve this issue
      Last edited by jasko_jacker; 10-24-2019, 08:01 AM.

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      • jasko_jacker
        Badcaps Legend
        • Oct 2014
        • 1137
        • italy

        #4
        Re: Asus switching drop

        Caps test:
        WCO Vent LoweSR 01/19 1000 mF

        1 - 997 0.8 Ohm .5%
        2 - 985 0.4 .5%
        3 - 1005 0.8 .6%
        4 - 1007 0.6 .6%
        5 - 1007 0.6 .6%
        6 - 973 0.5 .8%

        Comment

        • stj
          Great Sage 齊天大聖
          • Dec 2009
          • 30991
          • Albion

          #5
          Re: Asus switching drop

          those esr numbers are crap - they should really be more like 0.05 Ohms or better for low esr,

          Comment

          • CapLeaker
            Leaking Member
            • Dec 2014
            • 8132
            • Canada

            #6
            Re: Asus switching drop

            Change those 6 caps with new ones. The ESR on these is too high and should be more like what stj said.

            Comment

            • jasko_jacker
              Badcaps Legend
              • Oct 2014
              • 1137
              • italy

              #7
              Re: Asus switching drop

              I'm very sorry, I repeated the mesurement and about the electrolitic capacitors I made an error to report values,
              the measurement are 0.0X .
              I'm studying recently how the smps works but
              I think this is a very simple circuit, TL431,BJT,Zener,resistor and capacitors to
              drive the optocoupler to provide a feedback.
              I have tested individually each component of the
              cold part of this power supply and I have only a dubt about tl431 that I test only with a meter in diode mode and not with a test circuit.
              When I connect a load, on the anode of tl431, the voltage drop
              from 2.5 V to 2.0 V it should be insufficient to operate this shunt regulator. Without a load the voltage remain stable to 19V. If I remove the load the voltage not return to 19V
              Can I increase the capacity of C6 or replace it (I repair notebooks so I don't have this type of spares), could this component be the problem?
              I still have to test the optocoupler by unsoldering it. But with a tester and i place
              I think it's ok
              Attached Files
              Last edited by jasko_jacker; 10-27-2019, 04:19 PM.

              Comment

              • jasko_jacker
                Badcaps Legend
                • Oct 2014
                • 1137
                • italy

                #8
                Re: Asus switching drop

                I have removed the NPN, and without it seem that the voltage is stable.
                After that I substitute it (1AM) with BC846 but the drop returns.
                I have no experience with oscilloscope and I have avery entry level usb unit
                but I connect ch1 with opto IN and ch2 with opto OUT.
                It's a case that the voltage remain stable without transistor ?
                Attached Files
                Last edited by jasko_jacker; 11-03-2019, 10:43 AM.

                Comment

                • jasko_jacker
                  Badcaps Legend
                  • Oct 2014
                  • 1137
                  • italy

                  #9
                  Re: Asus switching drop

                  error
                  Last edited by jasko_jacker; 11-03-2019, 10:24 AM.

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