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    #1

    lenovo yoga 3 14"

    hi, i have a Lenovo yoga NM-A381, the main issue is that it will turn on first time when i disconnect the battery and power it on with adapter, after that when i shut it down, it won't boot again, the fans will spin for few seconds then they stop and keeps on looping. this machine turns on itself when power is connected(just like MacBooks) when power is connected for first time, all the voltages are fine, but after shut down and pressing power button, "EC_ON" jumps from 3.3v to 3.6 to 3.8v and this causes "+3VLP" to jump to 3.6 to 3.8v aswell and "+3VALW" drops to 2.4 to 2.7v.
    i usually repair MacBooks so don't have much experience in laptops, what should i try next?
    Tags: None
    #2
    Re: lenovo yoga 3 14"

    Make sure your multimeter batteries are good. +3VLP should never go to 3.8V, it is what's causing EC_ON to go to 3.8V as well. If you are 100% sure +3VLP indeed goes to 3.8V, then PU201 is probably bad.
    OpenBoardView — https://github.com/OpenBoardView/OpenBoardView

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      #3
      Re: lenovo yoga 3 14"

      Any update of this? I have the same problem with the same board, the only differnce is the +3VLP is still +3,2V. +3VALW goes to 2,25-2,7V.

      Comment

        #4
        Re: lenovo yoga 3 14"

        So although I still dont understand why, the solution for my case is to change U101, after that laptop works..

        Comment

          #5
          Re: lenovo yoga 3 14"

          Good evening, i have the Same model with a similar issue.

          MOD Edit: Link to schematic - https://www.badcaps.net/forum/showthread.php?t=65129

          History: bad GPU- & RAM-Controller. Gate from LowSide mosfet was shorted to ground on both ICs.

          After replacing both ICs i can do a "Cold Boot" (battery and Adapter disconnected and reconnected before) and It's booting to OS without Any issue. but if i shut it down and try to Power it on Second time, i get No Backlight, No Display, No BIOS (CapsLock-test), dimmed LEDs, etc.

          In my case the +3VLP is dropping from 3,3V to around 2,5V. i Wonder if the Voltage of B+ (thought it Has to be 19V) is okay? If Yes, i believe i have to replace PU201 too... The +5VLP Rail is working fine with Same Input Voltage.





          The weirdest Part is, it is working after Cold Boot, although i never get a PWRGD from this IC... o.O
          Attached Files
          Last edited by SMDFlea; 08-05-2023, 05:02 AM.
          FairRepair on YouTube

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            #6
            Re: lenovo yoga 3 14"

            Please confirm

            Ldo is not dropping

            If ldo drops in any case , ic will not go to next step

            Your output is dropping due to capacitor leakage or missing after coil and feedback value is not ok

            I am not an expert I think it is nvdc technology ,b+ feeder to every section as an input voltage , 8v approximately
            Last edited by stingerchamp; 12-27-2020, 09:32 PM. Reason: Thinking

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              #7
              Re: lenovo yoga 3 14"

              I can confirm the LDO isn't dropping, but The Phase on the Coil. And yes, It's NVDC, my first Laptop with a Charging Circuit Like this. Thank you, i'll Check the Caps First.
              FairRepair on YouTube

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                #8
                Re: lenovo yoga 3 14"

                Originally posted by sopik78 View Post
                So although I still dont understand why, the solution for my case is to change U101, after that laptop works..
                Tank you very much. I changed U101 and the laptop worked perfectly. It got very hot and must have disrupted the super I/O. I do not understand very well why it affected the + 3valw source ... This voltage did not rise more than 2.7v. and the power led was continuously blinking. I was desperate with this fault.
                We technicians exist because engineers need heroes too

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                  #9
                  Re: lenovo yoga 3 14"

                  Then you were more lucky than i was. While troubleshooting Once the Controller died completely and shorted 5V, EC and unfortunately PCH too. Now the Board is Just for spares...
                  FairRepair on YouTube

                  Comment

                    #10
                    Re: lenovo yoga 3 14"

                    @sopik78

                    You are a life saver. Thank you.
                    After removing U101 to confirm that the board will turn back on, it does!

                    Comment

                      #11
                      Re: lenovo yoga 3 14"

                      U101 = USB Load Switch.

                      Respectively, if removing this load switch works for you, this implies the load switch is defective and was shorted.

                      By removing U101 off the board, that local USB port or ports will no longer function since Vbus is no longer being passed through onto the connector(s).

                      You should seek out a replacement so that port will be functional once again.
                      Attached Files

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                        #12
                        Re: lenovo yoga 3 14"

                        I appreciate the concern. As mentioned I removed U101 to verify that it was causing the issue.

                        A replacement IC has been ordered and will make the replacement when arrives.

                        Comment

                          #13
                          Re: lenovo yoga 3 14"

                          Originally posted by introMac View Post
                          I appreciate the concern. As mentioned I removed U101 to verify that it was causing the issue.

                          A replacement IC has been ordered and will make the replacement when arrives.
                          Have you replaced U101 yet?

                          If it fixed the problem, would you please provide a URL for the replacement IC
                          better to keep quiet and be thought a fool, than to open your mouth and remove all doubt

                          Comment

                            #14
                            Re: lenovo yoga 3 14"

                            I tried removing U101

                            Didn't improve things unfortunately

                            It still won't start with battery connected

                            Only improvement it'll now start with power button, instead of having to use Novo button

                            Prerequisite still have to disconnect battery, then hold button while switching charger on

                            Win10 does detect a USB key though, a function I expected to lose with removal of U101

                            Everything else still the same as described in my original thread:

                            https://www.badcaps.net/forum/showthread.php?t=121843
                            better to keep quiet and be thought a fool, than to open your mouth and remove all doubt

                            Comment

                              #15
                              I legit signed up just to try and figure out what in the world is causing this stupid issue and why Lenovo hasnt taken care of it by now...

                              Comment

                                #16
                                It is a long thread. Which issue are you facing ? Usb port is defective? Or another fault?

                                Comment

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