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ASUS FX505DV no power shorted at PWM controller Pin 3 VREG3 TPS51225C, need pinpointing of the short.

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    #1

    ASUS FX505DV no power shorted at PWM controller Pin 3 VREG3 TPS51225C, need pinpointing of the short.

    (If anyone has a functional boardview file of FX505DV/DU that would be helpful)
    (Had 3 problems, now just 1)

    I have no experience or knowledge and usage of tools to repair devices besides the entire past 12-10 days of researching, watching YouTube repair videos and troubleshooting this laptop motherboard. ChatGPT was used as a guide to ask questions.
    I used boardviews of mostly FX505GD-M, and some FX505DU, FX505DD. Used schematics of FX505DU.

    I had originally intended to replace the BQ24780s first (due to previous battery removal while benchmarking) but I failed to notice the barely lifted trace of a white outline and the smell (sweet metallic smell, only noticeable when I placed my nose basically on the board (don't ask why)); just marked it down to being previously worked on and due to lack of knowledge; thinking it was normal minor motherboard defect.


    Click image for larger version Name: 20250408_200805.png Views: 41 Size: 11.42 MB ID: 3618850 Click image for larger version Name: 20250407_173429.png Views: 37 Size: 11.66 MB ID: 3618853
    Then the laptop would not power on which led to quick inspection and discovery of the destroyed trace, I soldered a jumper cable reconnecting JP8801 (It measures 20v on both ends once I replaced the Charger IC).

    When I installed the battery, the PWM controller IC instantly heated up, which led me to probing, discovering pin 3 shorted, tried replacing and measuring for shorts on the 2 capacitors (on 1st contacts to +RTC_POWER on both was shorted).
    Didn't work, pin 3 trace was still shorted, removing the IC and measuring the trace still detected the short. Placed the IC back. I am waiting for the replacement PWM IC to arrive and confirming if a faulty IC is the case.
    When the motherboard is plugged into the charger, it produces a high-pitched sound, no obvious signs of heat. This sound does not show up when battery is plugged in.

    Currently I'm stumped to where I can find the short as I'm assuming R8151 (0 OHM resistor) ends up being a bead of solder at the end of 3rd pin trace.(This measures short as well) And unsure where to start from 3VA / RTC_POWER and then towards the general 3V power rail to find the short.
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  • Answer selected by OOF DIO at 04-21-2025, 08:20 AM.
    Originally posted by OOF DIO View Post
    Correction: JP8801 measures 0.2v.
    Which means, even your Main Power Rail is not present right now.

    The floating track is most likely ACN or ACP, so for current sensing. If this track has touched another circuit, for example a 3.3V line, then it would explain what you are challenging right now.

    At least a shorted 3V LDO and from what i read still something wrong around the charging controller, so multiple issues.

    To blindly remove components is a very naive approach though. You need to inject voltage with a adjustable bench top power supply into this track. What is shorted will heat up then. Typical suspect is the embedded controller.

    I suggest to figure this first before continuing with the charging controller, since the damage could be already lethal for the motherboard.
    • Selected Answer

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      #2
      It's also shorted at +3VA_EC overall, pin 121 of the embedded controller sounds the short.

      Comment

        #3
        Correction: JP8801 measures 0.2v.

        Comment

          #4
          Originally posted by OOF DIO View Post
          Correction: JP8801 measures 0.2v.
          Which means, even your Main Power Rail is not present right now.

          The floating track is most likely ACN or ACP, so for current sensing. If this track has touched another circuit, for example a 3.3V line, then it would explain what you are challenging right now.

          At least a shorted 3V LDO and from what i read still something wrong around the charging controller, so multiple issues.

          To blindly remove components is a very naive approach though. You need to inject voltage with a adjustable bench top power supply into this track. What is shorted will heat up then. Typical suspect is the embedded controller.

          I suggest to figure this first before continuing with the charging controller, since the damage could be already lethal for the motherboard.
          FairRepair on YouTube
          • Selected Answer

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            #5
            I currently do not have an adjustable bench top power supply, I will purchase one soon. And will try to use electronic freezing spray to track the short.

            I am fearing the worst of what to do with the embedded controller since there are none of the same model available.

            As stated previously, I only have a couple of weeks experience in attempting any kind of repairs. And had to work with what I had on hand.

            I also have the option of returning the motherboard, getting a refund and opting for the 1660ti variant; which I hear is not far in terms of performance difference.

            Do you think there is any point in continuing with the repair? Or should I just give up and do what I stated above.

            Comment

              #6
              How do you think the lifted trace caused the floating track?

              Even with the old charging controller it was still shorted and I didn't even get 0.2V at JP8801 until I replaced the charging controller.

              I have a spare fx505DY motherboard and can attempt a transplant of that charging IC once I solve the short.

              Comment

                #7
                I think i have well explained already how the short circuit of VREG3 COULD have happened. Maybe you want to read that again. There is no clue though. Since it's just a assumption based on a mix of experience and knowing what circuits are affected. And the way to go, and in what order was explained too.

                The missing voltage at The current sense resistor or what you call JP8801 is the exact reason why I do assume a additional issue in the charging circuit still, since even with a missing or shorted 3V LDO the main power rail should work.

                tl;dr there is no direct correlation.

                Wait for the bench top PSU and act accordingly or come back for further assistance. And/or clarify about what (other) short you are talking about, in case there is a misunderstanding.

                EDIT: Not sure how you planned to handle the issues with the given knowledge and additionally assistance of ChatGPT (can't believe this detail tbh...), so if you have the opportunity to return this board although you have already "worked" on it, then I would strongly recommend it.
                Last edited by Sephir0th; 04-20-2025, 07:26 AM.
                FairRepair on YouTube

                Comment

                  #8
                  I mean if you thought you only had to replace the charging IC chip only to find out that a trace is broken and knew next to nothing about circuits let alone schematics you would do the same and turn to ChatGPT. I mean 13 days isn't nearly enough to gain the experience and knowledge to diagnose and fix this kind of motherboard repair from zero.

                  Another correction: The high pitched noise is coming from the charger IC chip.

                  The other short circuit that I found probing the embedded controller is on a similar 3V rail type +3VA_EC, most of the capacitors or the balls of solder that are linked to this rail contact all are nearly detected as ground.

                  And yes, I didn't have a plan, just hoped because it looked simple it would be simple and nothing else, since all it took was one tug on that trace I hoped putting it back would be that easy.

                  Comment

                    #9
                    You're right, I'm returning the board. As I intended it to be my daily driver.

                    Comment

                      #10
                      This a costly mobo and hence you should take comments at post#7 positively in your interest itself.

                      We're here to help you and not undermine your skills.

                      But think honestly if every laptop mb can be fixed in this forum ,How we professional people survive and get work?

                      Its always wiser to leave it to experts specially when stakes are high and knowledge/skills is not upto 100%.



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