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Asus VivoBook X540YA won't start, shuts down after 5 seconds

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    Asus VivoBook X540YA won't start, shuts down after 5 seconds

    Hello.

    I have a problem with my Asus X540YA PC, it starts and shutdown immediately after 5 seconds.
    Unfortunately I did not find the diagram of this motherboard (X540YA rev 3.0 motherboard, DAXKAFMB6E0 REV:E) and it is hard for me to find the real problem.
    I identified that all the voltages are good (5V, 3.3V, 0.9V, 1.5V, 1.8V) except those of the CPU.
    During the few seconds of starting the power consumption is 20 mA (no shortcut).
    I have read the BIOS and its contents is good.
    I think my problem is the absence of +12VSUS signal. The problem is that I do not understand how this voltage is generated, it seems to come from a network of shottky diodes (BAT54SDW) but I do not understand the voltage that I have noted.
    Below (photo 1) are the voltage that I note on this diode network on an assembly found on another Asus motherboard but which seems to use this same piece of assembly.


    I tested the diode array, without removing it from the board, and the diodes seem good except maybe the diode on pin 1 because the measurement with pins 2,4 and 6 indicates a capacitance of 95 nF with an ERS= 16 ohm. I don't know if this is normal considering that the component is soldered on the motherboard.
    I don't understand how this diode network works, I have the impression that input 1 (5V = +5VSUS) is correct. But what do you think about the voltage -9,7V on pin 6 ?
    In any case the result is that there is 0V on the output pin 5 which gives +12VSUS.

    Other mesure on the motherborad on photo 2.

    Thank you for your help.
    Attached Files
    Last edited by totof; 03-19-2023, 03:42 PM.

    #2
    Re: Asus VivoBook X540YA won't start, shuts down after 5 seconds

    This is a voltage multiplier, should be driven by the switching from P_12VSUS_VCLK_20. If switching is happening there, one of the diode is probably bad. Should remove it and test out of circuit, or just replace it if you have a donor board. Can also be one of the capacitor but less common.
    OpenBoardView — https://github.com/OpenBoardView/OpenBoardView

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      #3
      Re: Asus VivoBook X540YA won't start, shuts down after 5 seconds

      Originally posted by piernov View Post
      This is a voltage multiplier, should be driven by the switching from P_12VSUS_VCLK_20. If switching is happening there, one of the diode is probably bad. Should remove it and test out of circuit, or just replace it if you have a donor board. Can also be one of the capacitor but less common.
      Yes I agree, this is the track that I will explore (I have a doubt about one of the diodes).

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        #4
        Re: Asus VivoBook X540YA won't start, shuts down after 5 seconds

        I have removed the diode and it is bad.
        Now a have to buy another diode.
        To be continued ...
        Last edited by totof; 03-24-2023, 11:44 AM.

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          #5
          Re: Asus VivoBook X540YA won't start, shuts down after 5 seconds

          Make sure you eliminate the keyboard in your troubleshooting too. Most common failure I see on Asus (and Acer) laptops with integrated kb power buttons. Essentially, the ON/OFF line is held low, and the EC interprets this as the power button being held down, switching it off. Have a Vivobook on the bench with this exact problem. Fires up fine after a CMOS reset and disconnecting the kb.

          Asus keyboards are truly crap for this kind of thing, along with Acer.

          Comment


            #6
            Re: Asus VivoBook X540YA won't start, shuts down after 5 seconds

            Originally posted by reformatt View Post
            Make sure you eliminate the keyboard in your troubleshooting too. Most common failure I see on Asus (and Acer) laptops with integrated kb power buttons. Essentially, the ON/OFF line is held low, and the EC interprets this as the power button being held down, switching it off. Have a Vivobook on the bench with this exact problem. Fires up fine after a CMOS reset and disconnecting the kb.

            Asus keyboards are truly crap for this kind of thing, along with Acer.
            I have checked the kb power button and it is good.
            I hope the only problem is diode damage.

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              #7
              Re: Asus VivoBook X540YA won't start, shuts down after 5 seconds

              I changed the diode and now the pc restarts, problem solved.

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