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Asus X51L weird problem - continuous power cycling

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    #1

    Asus X51L weird problem - continuous power cycling

    I have this laptop in with a pretty weird issue. If you turn it on after it's been sitting for long, it will power on fine, but shut down by itself a few seconds afterwards. Sometimes it'll make it to the welcome screen but that's it.

    If you keep trying to start it, it will eventually drop into a continuous power cycling with the power LED flashing about every second or so, power button unresponsive. All rails seem to be present at their right voltages while it's on, and they all cycle along with the LED. 3.3v and 5v standby are good and stay stable. Nothing's getting hot.

    I would reball the NB but this seems to me more like a weird power issue. What do you think? Schematic attached.
    Attached Files
    Originally posted by PeteS in CA
    Remember that by the time consequences of a short-sighted decision are experienced, the idiot who made the bad decision may have already been promoted or moved on to a better job at another company.
    A working TV? How boring!
    Tags: None
    #2
    Re: Asus X51L weird problem - continuous power cycling

    Screwed power management IC?

    Only thing I saw that seems familiar, was a SMPS that was power cycling... normally you'd think shorted secondary parts or bad controller supply capacitor, BUT no shorts on the outputs, and all outputs were coming up (momentarily). Capacitor was fine. Controller Vcc was good.

    As a learning exercise I pulled and tested *everything* and everything passed.

    It was down to the transformer or the SMPS controller with integrated FET.
    New controller fixed the problem.
    "Tantalum for the brave, Solid Aluminium for the wise, Wet Electrolytic for the adventurous"
    -David VanHorn

    Comment

      #3
      Re: Asus X51L weird problem - continuous power cycling

      Just noticed i don't have Vcore. Or rather i have, but it's 0.02v then completely off. There is an ISL6262 in charge of Vcore. Scoped it and while it gets a steady 3.3v enable signal while the LED is on, i only see some oscillation on the gates of the high side FETs. Nothing on the low side.

      So i guess it's safe to say that the ISL6262 is damaged. I don't think i have one of those, i'll have to go buy it on Monday. I'll keep you updated.
      Last edited by Th3_uN1Qu3; 10-25-2014, 07:25 AM.
      Originally posted by PeteS in CA
      Remember that by the time consequences of a short-sighted decision are experienced, the idiot who made the bad decision may have already been promoted or moved on to a better job at another company.
      A working TV? How boring!

      Comment

        #4
        Re: Asus X51L weird problem - continuous power cycling

        This is weird. Without CPU i can see the gate drive waveform on both high side and low side FETs with my scope. It looks fine and has the right amplitude. Board still power cycles without CPU btw.

        With the CPU installed, i only get a brief pulse on the low side, and nothing on the high.
        Originally posted by PeteS in CA
        Remember that by the time consequences of a short-sighted decision are experienced, the idiot who made the bad decision may have already been promoted or moved on to a better job at another company.
        A working TV? How boring!

        Comment

          #5
          Re: Asus X51L weird problem - continuous power cycling

          ISL6262A damaged for sure. There was a short randomly appearing between gate and source of the high side FETs. Removed FETs, they tested ok. Short was still there on the board. Put FETs back on the board, short went away on one phase. Applied power, short came back on both phases. Removed ISL, no more short.

          Will replace ISL6262A and let you know how it goes.
          Originally posted by PeteS in CA
          Remember that by the time consequences of a short-sighted decision are experienced, the idiot who made the bad decision may have already been promoted or moved on to a better job at another company.
          A working TV? How boring!

          Comment

            #6
            Re: Asus X51L weird problem - continuous power cycling

            Ok, this board is officially voodoo. I thought i'd try to put the ISL6262A back on and give it one more shot and what do you know...

            Got CPU Vcore, board POSTed and booted just fine. Ran all possible tests on it - no problem. It's back together now and works great.

            The only thing i can think of is tin whiskers that grew under the QFN and shorted out those two outputs. While i was heating it, i pressed with my tweezers on the QFN to make sure it's soldered properly, and a couple small solder balls came out from underneath - which means that there was excess solder on the pad on the underside of the QFN. I had not added any.

            I don't think it could've actually been something inside the ISL6262A, as shorts in semiconductors don't just heal themselves. But it will remain a mystery.

            Either way, i'm happy that it works.
            Attached Files
            Originally posted by PeteS in CA
            Remember that by the time consequences of a short-sighted decision are experienced, the idiot who made the bad decision may have already been promoted or moved on to a better job at another company.
            A working TV? How boring!

            Comment

              #7
              Re: Asus X51L weird problem - continuous power cycling

              Tin whiskers shouldn't create excess solder, surely? Maybe there was just too much solder put on in the factory. Seems odd though. But stranger things have happened...
              "Tantalum for the brave, Solid Aluminium for the wise, Wet Electrolytic for the adventurous"
              -David VanHorn

              Comment

                #8
                Re: Asus X51L weird problem - continuous power cycling

                Originally posted by Agent24 View Post
                Tin whiskers shouldn't create excess solder, surely? Maybe there was just too much solder put on in the factory.
                I didn't imply that. I just noticed that there was excess solder underneath the QFN as i resoldered it.

                There are several traces that have the via under the QFN, close to the soldered pad (which of course, is grounded). It's not out of the question that over time, some tin whiskers could've grown under there long enough to touch the pad and thus short that trace to ground.

                I'll keep the laptop until Monday and if all remains good, it will be going back to the client.
                Last edited by Th3_uN1Qu3; 10-25-2014, 04:18 PM.
                Originally posted by PeteS in CA
                Remember that by the time consequences of a short-sighted decision are experienced, the idiot who made the bad decision may have already been promoted or moved on to a better job at another company.
                A working TV? How boring!

                Comment

                  #9
                  Re: Asus X51L weird problem - continuous power cycling

                  Originally posted by Th3_uN1Qu3 View Post
                  I didn't imply that. I just noticed that there was excess solder underneath the QFN as i resoldered it.
                  Sorry, you're right, I didn't read your post correctly.
                  "Tantalum for the brave, Solid Aluminium for the wise, Wet Electrolytic for the adventurous"
                  -David VanHorn

                  Comment

                    #10
                    Re: Asus X51L weird problem - continuous power cycling

                    It already left yesterday night. I called the owner so he could pick it up today, but he happened to be in the area so why not.

                    No complaints so far, and i hope it stays this way. Either way, this remains the "mystery board". I have no idea what caused it to behave this way, what matters is that it's fixed.
                    Originally posted by PeteS in CA
                    Remember that by the time consequences of a short-sighted decision are experienced, the idiot who made the bad decision may have already been promoted or moved on to a better job at another company.
                    A working TV? How boring!

                    Comment

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