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Macbook Air A1466 Fluctuating 3v supply

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    Macbook Air A1466 Fluctuating 3v supply

    Hello
    I got this unit with orange light but wont boot up
    I notice that its L7560 3.3v supply is fluctuating
    this is the reading I got on its PWM U7501 TPS51890A
    pin 4- EN1 - 0v
    pin 12 - EN - 3.3v Fluctuate
    pin 21 - EN2 - 3.3v Fluctuate
    pin 22 - vreg3 - 3.3v ok
    pin 23 - vin - 8.62V
    pin 29 - vreg5- 5v fluctuate

    I already check the power rails line in page 62 but I didn't find any short on those lines. I already tried replacing the pwm but same issue.
    I hope you can guide me where I can look for the fault of this unit

    #2
    Re: Macbook Air A1466 Fluctuating 3v supply

    What is the ppbus_g3h voltage to ground? (Check at the fuse)

    Is the 3v42 rail stable?

    Comment


      #3
      Re: Macbook Air A1466 Fluctuating 3v supply

      ppbus_g3h- 8.62v
      3v42 is stable
      current stuck on 0.02A

      Comment


        #4
        Re: Macbook Air A1466 Fluctuating 3v supply

        What is the 820-**** board number for your unit ?

        Comment


          #5
          Re: Macbook Air A1466 Fluctuating 3v supply

          Remove all power. Meter in resistance mode.

          What is the resistance to ground of PP3V3_S5_REG_R ? (L7560)

          Comment


            #6
            Re: Macbook Air A1466 Fluctuating 3v supply

            820-0165 sir

            What is the resistance to ground of PP3V3_S5_REG_R ? (L7560) - 400 ohms

            Comment


              #7
              Re: Macbook Air A1466 Fluctuating 3v supply

              400 ohms
              That is too low of a resistance for this rail. This is likely causing the fault with the current sense loop observing a heavy load and power pulsing this rail.

              With flux and patience, lift up one leg of L7560.

              Then measure the resistance to ground again on the PCB pads of L7560.

              Which side has this 400 ohm resistance to ground ?

              Is it producer side (U7501) or the consumer side (L7560, pin # 2) ?

              Do you have an adjustable power supply that can support 1 volt (NOT HIGHER)?

              Comment


                #8
                Re: Macbook Air A1466 Fluctuating 3v supply

                consumer side pin 2
                Yes i got a PSU Bench here and also thermal cam but it is in the shop im at home right now, only psu is available

                Comment


                  #9
                  Re: Macbook Air A1466 Fluctuating 3v supply

                  Do wait for other comments but there is someone who is partially shorted on this consumer side of the rail.

                  Suggestion is to inject 1 volt (not higher) but ok to use higher current. The idea is to heat up the defective part and use your thermal camera to locate that part.

                  You want to keep the voltage as low as the lowest power rail in case a high side mosfet is leaking (ie. that may power the CPU rail). The CPU cannot handle a high voltage.

                  Hoping that the short is a shorted capacitor (most likely - the tantalums are the worst for this but have seen ceramic non-polarized caps as well with the same fault).

                  Comment


                    #10
                    Re: Macbook Air A1466 Fluctuating 3v supply

                    ok sir thanks for your guide, I try to check all the power rails and I dont see any shorted circuit, I just try to intect this 3v line tomorror,

                    Comment


                      #11
                      Re: Macbook Air A1466 Fluctuating 3v supply

                      Tomorrow, also check the resistance to ground of vreg5 (pin 29) which you have reported is also fluctuating ?

                      Comment


                        #12
                        Re: Macbook Air A1466 Fluctuating 3v supply

                        Take off the heatsink from the CPU and check the PCH portion of the die for damage. Also check resistance to ground of L7630. Seen these shattered and you can just be wasting your time.

                        Comment


                          #13
                          Re: Macbook Air A1466 Fluctuating 3v supply

                          i tried to hang up the L7630 and the fluctuate stop, I will check now the CPU now

                          Comment


                            #14
                            Re: Macbook Air A1466 Fluctuating 3v supply

                            Originally posted by reformatt View Post
                            Take off the heatsink from the CPU and check the PCH portion of the die for damage. Also check resistance to ground of L7630. Seen these shattered and you can just be wasting your time.
                            I open the heatsink and the cpu is looks good no crack on the top of it

                            Comment


                              #15
                              Re: Macbook Air A1466 Fluctuating 3v supply

                              You need to get to stable PP3V42_G3H, PPBUS_G3H (8.6V no battery), and PP3V3_S5. Then troubleshoot from there with PM_SLP_S4.

                              Comment


                                #16
                                Re: Macbook Air A1466 Fluctuating 3v supply

                                PM_SLP_S4 not generated,
                                i check the 11 signal
                                1. PPVRTC_G3H - 3.42v
                                2. RTC_RESET_L - 3.42v
                                3. PCH_SRTCRST_L - 3.42v
                                4. PCH_INTVRMEN - 3.3v
                                5. PCH_DSWVRMEN_L - 3.24v
                                6. SYSCLK_CLK32K_RTCX1
                                7. PP3V3_S5 - fluctuate
                                8. PM_DSW_PWRGD - 0
                                9. PP3V3_SUS - 0
                                10. PM_BATLOW_L - Fluctuate
                                11. PM_RSMRST_L - 0
                                +1. PM_PWRBTN_L - Fluctuate
                                I thinks my main issue is this PP3V3_S5

                                Comment


                                  #17
                                  Re: Macbook Air A1466 Fluctuating 3v supply

                                  PP3V3_S5 resistance to ground on a working board should be over 3K. You said earlier this was 400 ohms so something is not right there which is why I said you look at the PCH first. The supply should still be stable even with that low resistance.

                                  Look for corrosion on U7501, especially near pins 9 through 16 as I often see liquid damage here.

                                  Comment

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