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    ASUS G731 shorted motherboard

    Hi, got this Asus ROG G731 with a "shorted motherboard", at least there are shorts measuring across a bunch of electrolytic decoupling caps. Probably been exposed to a faulty charger / wrong polarity charger.

    At least, inside I found a working 512GB SSD and 16GB of ram.

    Anyone have any service manual to this guy or any advice where to focus my probing ?
    Attached Files

    #2
    Re: ASUS G731 shorted motherboard

    Originally posted by PowerAmpFreak View Post
    Hi, got this Asus ROG G731 with a "shorted motherboard", at least there are shorts measuring across a bunch of electrolytic decoupling caps. Probably been exposed to a faulty charger / wrong polarity charger.

    At least, inside I found a working 512GB SSD and 16GB of ram.

    Anyone have any service manual to this guy or any advice where to focus my probing ?
    laptop schematic requests go here: https://www.badcaps.net/forum/forumdisplay.php?f=41 .Find the white silkscreened part number,it will probably be on the other side of the board
    All donations to badcaps are welcome, click on this link to donate. Thanks to all supporters

    Comment


      #3
      Re: ASUS G731 shorted motherboard

      Thanks, so you mean I will need to start the process by getting the MB out of the unit firstly, loosening the heatpipes and everything else ?

      Comment


        #4
        Re: ASUS G731 shorted motherboard

        Originally posted by PowerAmpFreak View Post
        Thanks, so you mean I will need to start the process by getting the MB out of the unit firstly, loosening the heatpipes and everything else ?
        Yes ,you`ll have to take the board out. Remove the heatsink screws a few turns out each evenly until theyre all loose,then try and lift the heatsink off near the screw area,if you lift it by the fan end it`ll bend like a banana
        Last edited by SMDFlea; 01-17-2022, 11:22 AM.
        All donations to badcaps are welcome, click on this link to donate. Thanks to all supporters

        Comment


          #5
          Re: ASUS G731 shorted motherboard

          Adding some pictures of the bottom side aswell.

          Obviously there is a G531 GT rev 1.5 motherboard I am looking for the service manual for.
          Attached Files

          Comment


            #6
            Re: ASUS G731 shorted motherboard

            It seems as far as I can understand, that the system power bus is shorted.
            All the electrolytes with a 25V rating are less than 1ohm across...

            I wonder if I should try to supply some current limited voltage through the charger input?
            I have a high resolution thermal camera that I could use to see if there are any heating stuff...
            Attached Files

            Comment


              #7
              Re: ASUS G731 shorted motherboard

              Post the resistance to gnd on those caps,and all the large square grey coils
              All donations to badcaps are welcome, click on this link to donate. Thanks to all supporters

              Comment


                #8
                Re: ASUS G731 shorted motherboard

                Here you are...

                Measured to GND with LCR meter.

                EDIT: Listen to this:
                I connected a heavily current limited supply across the short. Slowly increased the voltage to 100mV, current consumption increased to around 50mA initially and slowly faded down.
                After this the static short is gone.

                Hmm....
                Attached Files
                Last edited by PowerAmpFreak; 01-18-2022, 12:11 PM.

                Comment


                  #9
                  Re: ASUS G731 shorted motherboard

                  When doing voltage injection usually one starts with 1 V DC and current limit set to 2 A, since this will not cause any damage. 50 miliamps will cause nothing to significantly heat up.

                  Comment


                    #10
                    Re: ASUS G731 shorted motherboard

                    I suspect a MLCC ceramic cap somewhere on the system bus to be shorted. Eventually by injecting a small current will affect the MLCC material properties. I got the information from the previous laptop owner that it was dropped onto the floor and perhaps this damaged a MLCC.
                    Normally, MLCC are quite sensitive to mechanical stress and I will now go through them with freeze spray and measure resistance and see any change.

                    Comment


                      #11
                      Re: ASUS G731 shorted motherboard

                      Look at this video:
                      https://youtu.be/WU8_eTglue0

                      You can learn about the basic troubleshooting procedures.

                      Comment


                        #12
                        Re: ASUS G731 shorted motherboard

                        Question, does ASUS laptops detect the presence of a charging plug attached other than measuring the incoming voltage?
                        Apart from DC in, there are two small pins which could be some kind of detection pins or similair..

                        Comment


                          #13
                          Re: ASUS G731 shorted motherboard

                          Originally posted by PowerAmpFreak View Post
                          Here you are...

                          Measured to GND with LCR meter.

                          EDIT: Listen to this:
                          I connected a heavily current limited supply across the short. Slowly increased the voltage to 100mV, current consumption increased to around 50mA initially and slowly faded down.
                          After this the static short is gone.

                          Hmm....
                          hello, please measure the resistance to ground of the current sensing resistor, its usually located after the dc-in mosfets

                          Comment


                            #14
                            Re: ASUS G731 shorted motherboard

                            It seems I found the problem in this motherboard.
                            The story is the following:

                            Previous owner dropped the laptop on the floor.
                            That destroyed the charging connector
                            He tried to replace the connector
                            He then accidently managed to short a 0402 MLCC by a solder bridge.
                            When fixed the bridge the short is gone.

                            What's left to understand is the post above, what the smaller pins in the charging connector does. If they are used to detect the charging plug. One pin is grounded, the other is not. The via hole for this pin was damaged in the process of connector replacement.

                            Comment


                              #15
                              Re: ASUS G731 shorted motherboard

                              Now it seem to work.

                              Comment

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