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820-2936 won't turn on(hasgreen light) no liquid damage

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  • 820-2936 won't turn on(hasgreen light) no liquid damage

    Hi,

    I received this macbook with not turning on issue.
    No liquid damage. The board was pretty dusty. But no sing of liquid damage.
    When I press the power button the fan spins up a little bit and that's it. It does not do the on-off loop.

    Here are the measurements:

    PPBUS_G3H 12.57V
    PP3V3_S5 3.3V
    PP5V_S5 5V
    RTC_G3H - 3V
    32kHz present
    Y25010 oscillates

    Looks like when I hit the power button every power rails are coming on except: CPU_VCORE.

    Checked U2800 and Y2805. Y2805 does not oscillate. I changed both Y2805 and U2800.

    What could this be?

    Thank you.

  • #2
    Did you check RTC signals to PCH??, R1800 to R1803, should be about 3V on PCH side... Also could be a short on PP5V_S3 line....... Could be C6521, shorted USB port...

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    • #3
      Yes, I checked RTC signals. I forgot to mention it in my first post. No short on PP5V_S3 over 20k ohm.

      Edit:
      I've also
      PP3V3_SUS - 3.3V
      PP1V05_SUS - 1.05V
      Last edited by bighead; 08-17-2016, 12:19 PM.

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      • #4
        If no liquid I would try BIOS first. Backup the old!!

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        • #5
          Definitely no liquid damage. I tried different BIOS, but same thing. I've two same non-working board here for parts. I also tried those BIOS on this board. Nothing changed.

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