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820-00281 No Power

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  • 820-00281 No Power

    So my second 820-00281 in as many weeks. Customer advises they were watching youtube when it just shut down no power. Have taken it in and board looks very clean but is exhibiting the following behaviour:

    With battery plugged in i'm not getting PPBUS generated and my charger isn't able to power the machine - my usb c ammeter just keeps cycling on and off. With the battery unplugged I am getting PPBUS voltage at 12.6V and correct negotiation of the charging voltage from the charger. The board however still won't power up i've checked some common voltages:
    PP3V3_SUS - present
    PPBUS - present 12.6v
    SMC_ON_OFF_L sits at 3.3v but does drop to 0v when power button pressed.
    SMC_LID sits at 3.3v when lid open and drops to 0v when lid closed

    When I initally connect my charger / usb c ammeter to the board when it's bare after negotiating the correct charger voltage I get a brief current surge to 1.5a then it drops down to 0.0a and stays there.

    I haven't delved to much further into this one yet however would appreciate any advice in where to look first or if there is any common issue with the behavior I have described!

  • #2
    If you get that high current pulse, means the board tries to start and many secondary voltages should appear in that moment.
    So check for pulse at all big coils.
    If no pulse, check for short then.
    Also check ALL_SYS_PWRGD.

    Comment


    • #3
      Seeing a quick pulse on the PP5V5_S4 and PP3V3_S4 power rails to 5v and 3.3v. ALL_SYS_PWRGD - missing, the S0 rails don't pulse - only seem to have S5 rails after the pulse. Should also add I checked PM_SLP_S4_L which is low 0v.
      Last edited by CRC2018; 1 week ago.

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      • #4
        So you get a pulse at PM_SLP_S5_L, but no reaction at all at PM_SLP_S4_L?
        Trigger SMC_ONOFF_L and check again.
        Also check P5VS4_PGOOD.

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        • #5
          Yes pulsing PM_SLP_S5_L - cannot seem to see any pulsing of PM_SLP_S4_L
          P5VS4_PGOOD is not present although R7801 seems good.
          Should add - no pulsing at all with SMC_ON_OFF_L only when i replug charger then i get the quick pulse then off to S5 state again.

          Should add as well that after more testing I am seeing a pulse on the S0 Rails for less than a second.
          Last edited by CRC2018; 1 week ago.

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          • #6
            "Seeing a quick pulse on the PP5V5_S4 and PP3V3_S4 power rails to 5v and 3.3v."
            In this case, P5VS4_PGOOD should pulse too.

            Post diode mode to ground at L7600.
            You may need to change U7650.

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            • #7
              Is better to use an o-scope to catch fast pulse on the coils.
              It will also show if the pulse reach the nominal value expected.
              ALWAYS check on coil output pin connected to filter capacitor.

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              • #8
                Diode reading at L7600:
                Pin 1 - 0.418
                Pin 2 - 0.417

                A scope is something I am thinking of investing in but currently do not own!

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                • #9
                  Then repeatedly trigger SMC_ONOFF_L and check for pulse at L7600 and P5VS4_PGOOD.

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                  • #10
                    after repeat checking yes P5VS4_PGOOD is pulsing up to 3.3v and at L7600 it's pulsing up to 5v.

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                    • #11
                      So PM_SLP_S4_L pulses.
                      In the same way, check PM_SLP_S3_L and all big coils.
                      Also check all power rails from page 74, Power FETs.

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                      • #12
                        PM_SLP_S3_L is also pulsing - all other rails (at big coils) appear to be pulsing.
                        One strange behaviour appears that PM_SLP_S0_L pulses to 3.3v then drops down to 2.75v and stays there after everything else has pulsed
                        Last edited by CRC2018; 1 week ago.

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                        • #13
                          Any pulse at L7211/21/31?
                          Turn it on on SMC bypass mode; let see what happens...

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                          • #14
                            Yes seeing pulses on L7211, L7221 and L7231 - i'll try smc bypass mode and see if it powers up

                            Comment


                            • #15
                              Update - in SMC bypass mode it starts and runs. So we looking at bad SMC? Presume i'll need to get a donor SMC off another 820-00281 or are the ones from the 12" Macbook compatible?

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