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Lenovo ideapad 520, NM-B452 not powering up

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    #1

    Lenovo ideapad 520, NM-B452 not powering up

    Hey, I'm repairing a board from liquid damaged laptop, managed to get 5V and 3.3V rails up, some passives were corroded away. Only problem right now is no reaction to power button, there is no PCH_PWR_EN signal, DPWROK_EC is 2.5V, +1.0VALW is missing. Replaced KBC with brand new one, reprogrammed. No change. Any ideas? Schematic and boardview are available, attached them at the bottom. Boardview file can be opened by "BoardViewer" software.



    Please don't mind the damage near UC4, it was caused by liquid damage and there is battery connector on the other side, had to cut out the top trace and remove carbon. It's not important for now.
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    #2
    Post a link to the schematics please ! https://www.badcaps.net/forum/troubl...f-this-section
    All donations to badcaps are welcome, click on this link to donate. Thanks to all supporters

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      #3
      Originally posted by SMDFlea View Post
      Post a link to the schematics please ! https://www.badcaps.net/forum/troubl...f-this-section
      Schematics and boardview files: https://www.badcaps.net/forum/troubl...82#post1519682

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        #4
        Measure resistance to GND on PL500. check all the enables of PU500. I beleive 1.8VALW is also missing.

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          #5
          Originally posted by mcplslg123 View Post
          Measure resistance to GND on PL500. check all the enables of PU500. I beleive 1.8VALW is also missing.
          Resistance to ground on PL500 = 47.5 Ohm

          +1.0VALW_EN (PCH_PWR_EN) = 0V
          +2.5V_DDR_EN = 0V
          +1.8VALW_L_EN = 0V
          +1.05VGS_B_EN = 0V
          VDDQ_EN = 0V
          VTT_EN = 3.16V
          PMIC_EN = 2.9V

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            #6
            What is more interesting is that when I take off the ground probe, then touch +1.0VALW_EN with my other probe, suddenly the power draw jumps up from 8 to 17mA and +1.0VALW_EN becomes present:

            +1.0VALW_EN (PCH_PWR_EN) = 2.34V
            +1.0VALW on PL500 = 1V

            Must be some static charge effect that latches the signal up.

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              #7
              Resistance to GND on PL500 seems ok. Have you checked the motherboard for corrossion under microscope?

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                #8
                Originally posted by mcplslg123 View Post
                Resistance to GND on PL500 seems ok. Have you checked the motherboard for corrossion under microscope?
                Yes, documented corrosion spots then put it through ultrasonics, board is spotless.

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