Asus S500 --something I've never seen before.

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  • k370
    Member
    • Oct 2014
    • 30
    • portugal
    #1

    Asus S500 --something I've never seen before.

    Hi,

    I have something I've never seen before.

    I've received an Asus laptop that had a short in the DC input. I found that the second MOSFET in the DC input line was heating up, so I replaced it, and now the laptop works. Great, isn't it?



    Now, for the odd part: the mosfet replaced wasn't measuring as short or having low impedance on the board either before or after I replaced it. It was an "A5 GND" mosfet, which I swapped for something I had in stock—some N-type 30V MOSFET.

    Now the laptop works fine, but when it restarts, it takes 5 to 7 minutes before it's able to power on.



    For example:

    The laptop runs fine in Windows, but if I restart it, when it shuts down and tries to boot back up, it won't do it right away. I have to wait 5 to 7 minutes for it to actually start again.
    This behavior is the same whether using only the battery, only the charger, or both.

    When it doesn't start, it behaves almost like it has a short in some secondary line. I press the power button, the lights come on, the hard drive spins up, and then it shuts down immediately—this takes around 1 to 2 seconds.



    Does anyone have a clue as to what could be causing this behavior? The time the laptop is on doesn't affect the wait time before it can start again. I've searched for schematics to help troubleshoot, but I haven't found anything.

    The motherboard code is 60NB0060 rev 2.1, and the laptop model is an Asus S500CA.

    Thanks in advance!
    ​
    Tags: None
    • mon2
      Badcaps Legend
      • Dec 2019
      • 14239
      • Canada
      #2
      Which charger IC is onboard?

      Check the ACDET pin on the charger ic to confirm it is within normal range with the power adapter. You may have another leaky mosfet onboard. Remove all power and check the resistance across the mosfet pins. Each measurement should be hundreds of k ohms or higher.

        Comment

        • k370
          Member
          • Oct 2014
          • 30
          • portugal
          #3
          Originally posted by mon2
          Which charger IC is onboard?

          Check the ACDET pin on the charger ic to confirm it is within normal range with the power adapter. You may have another leaky mosfet onboard. Remove all power and check the resistance across the mosfet pins. Each measurement should be hundreds of k ohms or higher.
          Hi,
          After looking with more attention, I found the schematics, and the actual model of my board is S400CA rev 3.1.

          The MOSFET I changed seemed like it was shorted, but it wasn't. The issue was with PQ8802, and the original MOSFET reference is (P0903BEA).

          The charging IC on my board is BQ24725ARGRR, and the ACDET pin shows 2.60V, whether the laptop is in a cold state (when it turns on) or a hot state (when it doesn't turn on).

          I've measured all the MOSFETs present on the board, as well as a good amount of capacitors, and everything seems fine.

          Do you have any other ideas?

          I've also included the MOSFET I replaced and the boardview for reference. LINK to boardview https://www.badcaps.net/forum/docume...ptop-boardview
          Attached Files
          Last edited by SMDFlea; 10-23-2024, 03:47 AM. Reason: LINK to boardview

            Comment

            • reformatt
              Badcaps Legend
              • Feb 2020
              • 1413
              • Australia
              #4
              I would check power good signals for each power rail back to the EC with the board on the bench. Have seen intermittent issues with BAT54CW/BAT54AW diodes (e.g. D2201/D2202) causing these to be low etc. Power sequence halts as a result.

                Comment

                • k370
                  Member
                  • Oct 2014
                  • 30
                  • portugal
                  #5
                  I've solved this... hurray!

                  It was the BIOS; I used the dump from this link, and now everything works marvelously!
                  ​

                  https://www.badcaps.net/forum/troubl...s400ca-rev-3-1

                    Comment

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