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820-3437 bad SMC or CPU?

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  • 820-3437 bad SMC or CPU?

    Currently working on a 820-3437 where power supply is pulling .02Amps. Device has no signs of liquid damage. Always present power rails are present. SMC_RESET_L is present. PM_SLP_S4_L is missing. Board does not boot in SMC Bypass. I discovered the tiniest amount of corrosion under SMC on Pad 64 which is SMC_PWRFAIL_WARN_L. Did not find corrosion anywhere else on board. I reflowed SMC to remove the corrosion and device still pulls .02Amps and does not boot in SMC Bypass. Before I spend the time pulling off SMC and Reballing, is this a sign of a dead CPU?

    Sorry for the brief explanation.

  • #2
    Try another SMC to be safe. If no change, could literally be anything including the CPU causing no S4. Inspect as closely as possible for corrosion elsewhere.

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    • #3
      Sounds good. Will follow up after SMC Replacement.

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      • #4
        What about PM_BATLOW_L?
        Magsafe 2 charger for sure?

        Check if PM_PWRBTN_L reacts when triggering SMC_ONOFF_L; use R5115/16 pads for this.
        Be sure PM_RSMRST_L is high.

        Do you get PM_SLP_SUS_L?
        If not, check all PCH's RTC signals.

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        • #5
          Yeah actually check BATLOW first.

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          • #6
            It took a while to revisit this board but I am back at it. I have not replaced the SMC yet.

            Using both orginal 85 watt magsafe 2 and DCPS with genuine 85 watt magsafe 2 connector attached.
            PM_PWRBTN_L drops from 3.4v to .04v when triggering SMC_ONOFF_L
            PM_RSMRST_L = 3.3v
            PM_SLP_SUS_L = 3.3v

            BATLOW = 0.037v

            PM_SLP_S5_L is missing.

            I see that BATLOW comes from SMC.

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            • #7
              "PM_PWRBTN_L drops from 3.4v to .04v when triggering SMC_ONOFF_L"
              Check if any PM_SLP_Sx_L signal reacts at same time.

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              • #8
                PM_SLP_SUS_L = Stays at 3.3v
                PM_SLP_S5_L = stays at 0v
                PM_SLP_S4_L = stays at 0v
                PM_SLP_S3_L = stays at 0v
                PM_SLP_S0_L = stays at 0v

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                • #9
                  I removed the SMC and behold, there was a hole in the SMC. Image attached. I am replacing the SMC now to resolve issue.
                  Attached Files

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