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MacBook Air 820-3435 - no power

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  • MacBook Air 820-3435 - no power

    first post ... please be gentle (my hair is already very grey).

    I am trying to repair a mac air mid 2013 with an 820-3435 B logic board. Wine spill on right hand side of keyboard.

    some noticeable corrosion gunk on the board but all looked rather old; so probably predated the recent spill. no noticeable liquid residue on the SMC side of the board

    the liquid damage tell-tale under the lcd connector was bright red. There was some gunk on the connector itself and the pins, but no pad damage, and no evident burning.

    Fuse F7770 was burned out, and the cap next to it (C7782) was crisped on one side but still measuring 100nF. so light cooked rather than cindered. I've removed it for the time being anyway.

    green light comes on with the charger. Doesn't turn orange but no battery connected. I've fluxed up the SMC and given it some heat. only to about 140C though.

    the power rails are as follows:

    PPBUS_G3H 8.2v
    PPBUS_S5_HS_COMPUTING_ISNS 8.2v
    PPBUS_S5_HS_OTHER_ISNS 8.2v

    PPDCIN_G3H_ISOL 16.5v
    PPDCIN_G3H 16.5v

    PP3V42_G3H 3.3v
    PPVRTC_G3H 0.6v
    PP5V_S5 0.5v
    PP5V_S4RS3 0.5v
    PP5V_S0 1.16v


    diode mode measurements to ground
    PPBUS_G3H 0.131v
    PP3V42_G3H 0.266v
    PP5V_S5 0.413v
    PPVRTC_G3H 0.576v

    nothing gets evidently hot. the SMC is perhaps 8C above ambient.

    can anyone suggest a diagnosis or steps to take to get closer to one? I don't have any suitably sized components for swap outs so can't go a trial and error route unfortunately!

    many thanks in advance.
    Justin

  • #2
    You are going to need parts. I would start with measuring resistance to ground on PPVRTC_G3H and check the clock chip area and U5110 area.

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    • #3
      8.2 volts on PPBUS means the SMC isn't turning on. Tried a known good flat cable and I/O board? Voltage on SMC_RESET_L? After that the clock circuit needs to be addressed need 3.3 volts steady on PPVRTC_G3H.

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      • #4
        Originally posted by rvanpruissen View Post
        You are going to need parts. I would start with measuring resistance to ground on PPVRTC_G3H and check the clock chip area and U5110 area.

        thanks for the replies. Appreciate that I will need parts. Mouser supports my area of france adequately, if not rapidly.

        resistance to ground from PPVRTC_G3H is 161.5kOhms

        on U5110 the voltages are:

        pin 1 3.33v
        pin 2 0
        pin 3 3.3v //PP3V42_G3H_SMC_SPV
        pin 4 1.8v //SMC_MANUAL_RESET_L
        pin 5 0.65v //SMC_RESET_L
        pin 6 3.26v //SMC_LSOC_RST_L
        pin 7 3.29v //SMC_ONOFF_L
        pin 8 3.29v //PP3V3_S5_AREF_SMC


        Is it odd that SMC_RESET_L is being driven low? It is not shorted to ground (16MOhm or so). The pull up resistor is good although measuring (in circuit) as 70k rather than 100k.

        i've prodded around some of the clock circuit and nothing seems odd apart from the voltage. But tbh I'm not sure what I should be checking. could the clock chip be bust?

        <later, after a gin and tonic>
        so ...I reflowed the clock chip, and now get the green charger light turning orange after 3 seconds. so that's an improvement, I guess?

        after reflowing the clock chip I get 8.6v back on PPBUS, 3.42v on PP3V42_G3H and 1.6v on SMC_RESET_L

        but nothing on PPVRTC_G3H

        so perhaps there was a short under the clock chip, now gone with reflowing but the clock chip is bust?

        advice gratefully received.

        thanks
        Justin


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        • #5
          Replace the clock chip as it will have corroded pads under it, same with U5110 really. Also remove J6100 to avoid corrosion issues under it.

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          • #6
            I took the clock chip off and checked before reflowing it. It looked fine. The original gunk went with the removal.

            Would absence of ppvrtc prevent power on?

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            • #7
              Yes, PPVRTC must absolutely be there. Replace the chip and check again.

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              • #8
                Thanks Duke

                parts ordered so I'll report back when they're on the board.

                Comment


                • #9
                  any update here?

                  Comment


                  • #10
                    Good question! This is in the pile of things to do. I will try to resurrect it tomorrow and report back.

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