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2017 Apple MacBook Pro 13 inch touchbar A1706 - Not turning on - PPBUS Short?

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    #1

    2017 Apple MacBook Pro 13 inch touchbar A1706 - Not turning on - PPBUS Short?

    Hi all,

    Is there a boot-up sequence for the A1706 (Kaby lake) to see where the computer is getting stuck? Equiv to the below for older MBP's?
    https://logi.wiki/index.php/G3_to_S3..._and_Broadwell

    currently I measure:
    PP20V_USBC_XB_VBUS = 20
    PPDCIN_G3H_CHGR = 20.4
    PPDCIN_G3H = 20.4
    SMC_RST_L = 3.4
    PM_EN_P3V3_G3H = 5.2
    PP3V3_G3H = 3.4
    PPBUS_G3H = 0V (2.1 Ohm to GND - ISL9239 failure?)

    S5:
    PP3V3_S5 = 0
    PP5V_S5 = 0.346
    PPBUS_HS_OTH3V3 = 0.0186
    PPBUS_HS_OTH5V = 0.0186

    Obv:
    ALL_SYS_PWRGD = 0

    What should the resistance to GND be for these inductors? They're all <8 Ohms, looks like there could be a short in that area but I’m not sure in typical values:
    L7430
    L7420
    L7410
    L7210
    L7220
    L7270

    Also accross C10G1 is 5.5 Ohms
    and the footprint for C1161 2.935 Ohm

    anyway, other info like CPU power-up requirements would be appreciated
    Last edited by BillyJ; 01-02-2022, 04:04 PM. Reason: Clarity
    Tags: None
    #2
    Re: 2017 Apple MacBook Pro 13 inch touchbar A1706 - Not turning on - PPBUS Short?

    Hi.

    1) what is the board # for your logic board ? 820-xxxx format.

    2) Remove F7000 fuse that is in series with the output of the PPBUS_G3H rail.

    Then, meter in resistance mode & no power to the logic board, check and post the resistance to ground for the F7000, pad #1 and then pad #2.

    Interested to know if the very low resistance to ground is BEFORE the fuse or AFTER the fuse.

    Do not inject any voltages at this time - just confirming which side of the fuse is this heavy load.

    Suspecting a bad cap downstream but let us confirm this detail. If indeed the low resistance is AFTER the fuse then power up without the fuse on the circuit board and check if the PPBUS_G3H is normal BEFORE the fuse. All this testing without the fuse onboard.

    Comment

      #3
      Re: 2017 Apple MacBook Pro 13 inch touchbar A1706 - Not turning on - PPBUS Short?

      Thanks for your reply!

      I haven't had a chance to remove the fuse but found a 1.12 ohm short across a very burnt C3505.

      I will pull it off and check the fault goes tomorrow.

      To answer your q about the board number:
      820-00923 A

      Comment

        #4
        Re: 2017 Apple MacBook Pro 13 inch touchbar A1706 - Not turning on - PPBUS Short?

        but found a 1.12 ohm short across a very burnt C3505.
        THAT could be the show stopper!!

        Comment

          #5
          Re: 2017 Apple MacBook Pro 13 inch touchbar A1706 - Not turning on - PPBUS Short?

          haha my thoughts exactly! It could definitely pull PPBUS_G3H down so hopefully that's the only fault.

          Couldn't see it yesterday as the motherboard was still in the machine due to a screw which was rounded out. Ended up doing lots of masking and then Dremel-ing a slot into the head to remove. That wasn't fun - would not recommend

          Comment

            #6
            Re: 2017 Apple MacBook Pro 13 inch touchbar A1706 - Not turning on - PPBUS Short?

            Not got access to the BRD file right now but I gave the wrong designator. It was not C3505 but instead one of the 33uF B3 case caps (C3502 to 3504).

            I removed that and the short had gone so replaced it with 3 parallel 10uF ceramic caps as that was all I had.

            before trying to power up and check the PPBUS_G3H rail, I'm unsure about those inductor to ground measurements...

            They're still <8 ohms on the group of inductors mentioned above which seems... sub-optimal.

            Comment

              #7
              Re: 2017 Apple MacBook Pro 13 inch touchbar A1706 - Not turning on - PPBUS Short?

              Some of the inductors are for very low voltage rails. Respectively, their resistance to ground will be low.

              Review the PPBUS_G3H rail again -> remove the fuse @ F7000.

              Then check & post the resistance to ground on BOTH sides of the F7000 PCB pads.

              Comment

                #8
                Re: 2017 Apple MacBook Pro 13 inch touchbar A1706 - Not turning on - PPBUS Short?

                good point... both those sets of inductors are for the 3 phase DCDC converters supplying I think 0.5 to 1.5V.

                I did apply 0.5V to them after that comment and took a look with a thermal camera. It didn't slam into the 0.2A current limit and there were no clear hotspots so I'm pretty confident I agree with you.

                So this F7000 removal, what am I aiming to learn? after changing that cap out, the resistance to ground from PPBUS_G3H (with F7000 fitted) settles at approx 39k. Very tempted to refit the logic board and power up now?

                Comment

                  #9
                  Re: 2017 Apple MacBook Pro 13 inch touchbar A1706 - Not turning on - PPBUS Short?

                  That is a healthy resistance. No more short on that rail.

                  Yes, if you can rebuild the parts that may have been removed / disabled, populate them back and check the voltage on PPBUS_G3H. Post your results.

                  Comment

                    #10
                    Re: 2017 Apple MacBook Pro 13 inch touchbar A1706 - Not turning on - PPBUS Short?

                    PPBUS 13v, job done.

                    All assembled and working now. Thanks for your help!
                    Last edited by BillyJ; 01-04-2022, 05:22 PM.

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