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820-3208 - no fan spin

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  • #16
    "If U2700 receives correct 3V42, and all caps from VRTC are good (disconnect them for test), then no other reason than bad PCH remains..."
    Did you check???

    PCH can have high resistance to ground, but it can enter in some kind of avalanche effect, droping VRTC...
    No matters SMC is good or not.
    Bad RTC block will not allow PCH starting power on sequence!


    • #17
      i used an RTC from a donor board. but since VRTC is the same as pp3v3_s5 I suspect the issue is not the clock chip but pp3v3_s5.

      i will double check the caps.

      the more interesting question, forensically, is that the board had fan spin when the resistor to all_sys_pwrgd was remove to prevent it pulling low. The heat sink was in place and, as said, fan spinning happily and normally. It then spontaneously stopped within the next twenty minutes. No apparent overheating (although I was not present). No evident corrosion.


      • #18
        PCH should work with 2.7V on VRTC.
        The suspect thing is if that voltage arrives to PCH as is, or is pulled down by PCH...

        Do you also have 2.7V at 3V3_S5 coil?
        If yes, check corresponding power supply.
        Pay atention to feedback resistors, R7260/61.


        • #19
          yes. with L7260 removed there is 2.6+v at both pads (which I find a bit odd and makes me suspicious of U7201)

          Interestingly R7260 and61 measure 11k and 7.8k respectievely . on a donor board they measure closer to 20 and 9k

          replaced the clock chip again. ppvrtc is at 2.3v now. PP3v3_s5 remains the same. I'm not getting a 32kHz signal on the clock chip though. starts at 16kHz and then spirals down to 8.


          • #20
            also to note that there is no 3v on the middle pin of the magsafe.

            U2700 receives pp3v42_g3h. i cannot see any cap that is bad around U2700. there is no short on that rail.

            But ... i cannot see the logic that says that the PCH must start up just because U2700 is working. doesn't the PCH need all_sys_pwrgd AND (U2750) CPUIMVP_PGOOD AND (U2760) SMC_DELAYED_PWRG to start up?
            Last edited by jpadie; 12-02-2018, 03:59 PM.


            • #21
              Mentioned signals appear much later...
              PCH should first release SLP_SUS and next SLP_Sx, after got PWRBTN reaction from SMC.

              "with L7260 removed there is 2.6+v at both pads"
              The coil is a part (important) of buck controller!!!
              Any voltage measure without coil is a non-sense...

              Change U7201 and Q7260; pay atention to R/C7264.


              • #22
                Yes - it's very odd. the voltage stays the same whether the coil is there or not. makes me very suspicious of U7201. but .... there is no enable inputer on U7201 either


                • #23
                  Post basic voltages for U7201 and U7941.


                  • #24

                    mostly at or close to 0mv except for
                    3 80mv
                    10 20mv
                    16 800mv
                    17 2.7v
                    18 2.7
                    22 3.3v
                    23 8.2v
                    24 2.7v
                    25 2.7v
                    26 2.47v

                    1 3.42v
                    2 0
                    3 0
                    4 3.39v
                    5 0
                    6 2.7v
                    7 0
                    8 0


                    • #25
                      As expected, missing SMC_PM_G2_EN. It comes from SMC.
                      You didn't mention incorrect PPBUS_G3H before...

                      Check SMC_RESET_L value.
                      Also try a reflow to SMC.


                      • #26
                        why do you think that PPBUS is incorrect? It is 8.2v.

                        SMC_RESET_L is high (as per message yesterday).

                        yes. missing SMC_PM_G2_EN as per the same previous message.


                        • #27
                          PPBUS_G3H correct value is aprox 8.4-8.5V.
                          8.2V means SMC don't talk with ISL6259!
                          And this be caused by SMC, or ISL6259, or something else connected on SMBattery Bus.
                          As you also miss SMC_PM_G2_EN, SMC is first suspect here.
                          The best option is change it. But I recommend to reball it first.


                          • #28
                            ah. that is interesting. PPBus has always been 8.2v even when the board was in an S0 state. definitely something fishy.

                            i will reflow the SMC later. I don't have any stencils here to do a proper reball of a donor.


                            • #29
                              I did many at hand; there are aprox 150 balls, not too many...
                              0.35-0.4mm for commodity, but you can also use 0.3, even 0.45mm.


                              • #30
                                ha. it is a plan ... but i am rather middle aged and have shaky hands!

                                i may try with some old donor boards one weekend!


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