Asus Vivobook x421a

Collapse
X
 
  • Time
  • Show
Clear All
new posts
  • DJbapt59
    New Member
    • Jan 2025
    • 6
    • France

    #1

    Asus Vivobook x421a

    Hello everyone,

    I recently picked up a laptop that was about to be thrown away to try to repair it. I've tested quite a few things, but I don't know where to look anymore. Could you please help me?

    Brand: Asus Vivobook
    Motherboard reference: x421da, Rev 2

    Context:
    The person who gave it to me mentioned it might have been exposed to water, but they weren't sure. After opening it up, I couldn't find any signs of water damage or oxidation on the motherboard.

    The first thing I did was to connect the PC to a power supply: 19V stable and 2.5mA of current draw.

    Voltage measurements:
    • 19V at the shunt resistor.
    • I then tested the voltages at all the coils, and they were all at 0V.

    I tried to locate the 3V/5V chip (boardview and schematics were impossible to find) but couldn't identify any chip with a matching reference and location.

    I did find two chips with the exact same reference (TPS51396A), located close to each other near the BIOS and the SIO. I thought they might handle 3V and 5V separately.

    I measured the voltages on these chips, and they have identical readings (see image TPS51396A.png). The chip is activated, so there should be voltage at the coil, but there isn't.

    Next steps:
    I disconnected the power supply and measured resistance between ground and various points (see board_picture.jpg): ​
    • Main power rail: O.L
    • 1 - Battery coil: O.L
    • 2 - Fan: O.L
    • 3 - Unknown: 0 Ohms
    • 4, 5 - 3V/5V?: 0 Ohms
    • 6, 7 - CPU: 2.5 Ohms
    • 8 - Unknown: 0 Ohms
    • 9 - RAM: 0 Ohms



    After that, I injected current step by step at coils 3 and 9 since their traces are the largest. At most, I used the following parameters for short durations (5 seconds): 0.05V - 3.5A (CC protection). I didn't notice any hot spots while using isopropyl alcohol (that's the only thing I have available).

    After checking the entire board and finding nothing, I tested the voltage at the main rail again, but there was no longer any voltage. I then tested the Vgate of the main rail MOSFET and observed a 12V spike repeating roughly every second on the oscilloscope; I believe a short circuit is being detected, and the MOSFET shuts off immediately.

    Resistance measurements remain the same as before the current injection, so there's no short on the main rail.

    Feel free to ask for more information. Thanks in advance to those who respond kindly—if I made any mistakes, I'm here to learn, and the PC was going to be thrown out anyway.
    Attached Files
  • rogfanther
    Badcaps Veteran
    • Jul 2006
    • 458
    • Brazil

    #2
    Please re-check those resistance measurements in the coils. One probe to ground, one probe at the coils.

    With those 0-ohm measurements, you should have some pretty nice shorts on the board.

    Comment

    • DJbapt59
      New Member
      • Jan 2025
      • 6
      • France

      #3
      Originally posted by rogfanther
      Please re-check those resistance measurements in the coils. One probe to ground, one probe at the coils.

      With those 0-ohm measurements, you should have some pretty nice shorts on the board.
      I check again; my probe are 0.8 Ohms... and those coils are 0.8 Ohms ... If only I had a thermal camera, it might be a very small component that I can't see with isopropyl alcohol

      Comment

      • Sephir0th
        Badcaps Legend
        • Oct 2020
        • 1262
        • Germany

        #4
        This is for sure a fried APU. And with such straight shorts you should feel something (after a while), even without thermal camera
        FairRepair on YouTube

        Comment

        • DJbapt59
          New Member
          • Jan 2025
          • 6
          • France

          #5
          Originally posted by Sephir0th
          This is for sure a fried APU. And with such straight shorts you should feel something (after a while), even without thermal camera
          Thanks for your answer
          If APU is fried, coils 6 and 7 would be 0 Ohms isn't it ?

          Comment

          • Sephir0th
            Badcaps Legend
            • Oct 2020
            • 1262
            • Germany

            #6
            That's a way to optimistic view. What I suspect being a shorted 3.3V, 0.9VS, 0.75V and a shorted RAM supply are enough indications for my taste.

            Move on, inject and observe will be the only way to figure
            FairRepair on YouTube

            Comment

            Related Topics

            Collapse

            • Document Archive
              ASUS VivoBook ASUS VivoBook 15 S513 FHD i5 16GB/512GB G3 SSD Notebook 15 Specification for Upgrade or Repair
              by Document Archive
              This specification for the ASUS VivoBook ASUS VivoBook 15 S513 FHD i5 16GB/512GB G3 SSD Notebook can be useful for upgrading or repairing a laptop that is not working. As a community we are working through our specifications to add valuable data like the ASUS VivoBook 15 S513 FHD i5 16GB/512GB G3 SSD boardview and ASUS VivoBook 15 S513 FHD i5 16GB/512GB G3 SSD schematic. Our users have donated over 1 million documents which are being added to the site. This page will be updated soon with additional information. Alternatively you can request additional help from our users directly on the relevant...
              09-07-2024, 02:50 AM
            • Document Archive
              ASUS VivoBook Vivobook Pro 15 OLED D3500QC-L1351W Notebook Pro 15 OLED Specification for Upgrade or Repair
              by Document Archive
              This specification for the ASUS VivoBook Vivobook Pro 15 OLED D3500QC-L1351W Notebook can be useful for upgrading or repairing a laptop that is not working. As a community we are working through our specifications to add valuable data like the Vivobook Pro 15 OLED D3500QC-L1351W boardview and Vivobook Pro 15 OLED D3500QC-L1351W schematic. Our users have donated over 1 million documents which are being added to the site. This page will be updated soon with additional information. Alternatively you can request additional help from our users directly on the relevant badcaps forum. Please note that...
              09-07-2024, 04:30 AM
            • Document Archive
              ASUS VivoBook VivoBook 14 Notebook 14 Specification for Upgrade or Repair
              by Document Archive
              This specification for the ASUS VivoBook VivoBook 14 Notebook can be useful for upgrading or repairing a laptop that is not working. As a community we are working through our specifications to add valuable data like the VivoBook 14 boardview and VivoBook 14 schematic. Our users have donated over 1 million documents which are being added to the site. This page will be updated soon with additional information. Alternatively you can request additional help from our users directly on the relevant badcaps forum. Please note that we offer no warranties that any specification, datasheet, or download...
              09-07-2024, 04:10 AM
            • Document Archive
              ASUS VivoBook S531FL-BQ127T Notebook S15 Specification for Upgrade or Repair
              by Document Archive
              This specification for the ASUS VivoBook S531FL-BQ127T Notebook can be useful for upgrading or repairing a laptop that is not working. As a community we are working through our specifications to add valuable data like the S531FL-BQ127T boardview and S531FL-BQ127T schematic. Our users have donated over 1 million documents which are being added to the site. This page will be updated soon with additional information. Alternatively you can request additional help from our users directly on the relevant badcaps forum. Please note that we offer no warranties that any specification, datasheet, or download...
              09-06-2024, 10:56 AM
            • Document Archive
              ASUS VivoBook S531FL-BQ033T Notebook S15 Specification for Upgrade or Repair
              by Document Archive
              This specification for the ASUS VivoBook S531FL-BQ033T Notebook can be useful for upgrading or repairing a laptop that is not working. As a community we are working through our specifications to add valuable data like the S531FL-BQ033T boardview and S531FL-BQ033T schematic. Our users have donated over 1 million documents which are being added to the site. This page will be updated soon with additional information. Alternatively you can request additional help from our users directly on the relevant badcaps forum. Please note that we offer no warranties that any specification, datasheet, or download...
              09-06-2024, 10:56 AM
            • Loading...
            • No more items.
            Working...