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820-3437 Reballed SMC and now low voltage on PPVRTC_G3H

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  • 820-3437 Reballed SMC and now low voltage on PPVRTC_G3H

    Hello,

    I have that board which used to have a nice 0V on SMC_PM_G2_EN.
    Since I've replaced the SMC it seems to be a steady 3.3V however I have now a 1.2V on PPVRTC_G3H that I don't recall having prior to the SMC replacement.
    I've replaced twice the clock chip and have checked all the incoming rails on the clock chip (which are present) but still this 1.2V

    Am I now facing a dead CPU here guys? :-(

  • #2
    Only one way to know. What is the resistance to ground on PPVRTC_G3H? Also there are capacitors on that rail, remove them and see what you get.

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    • #3
      I am getting 0.4v drop to ground on PPVRTC_G3H.
      Also I've checked that resistance to ground with another board and it is similar.
      Finally,I've checked all the resistor going to the PCH and the values are good.

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      • #4
        This makes no sense. Either PP3V3_S5/PP3V42_G3H are pulsing/low/missing, or resistance to ground is low on PPVRTC_G3H. Nothing else is going to cause this to be 1.2v besides the resistance magically going down when it is turned on.

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        • #5
          I agree with you however here is what I've done today:

          - Resoldered a new clock chip from pool of new chips (I also used some from donor boards previously)
          - Redone my solder around the chip a few times
          - Check for steady PP3V42 and PP3V3 voltages with my oscilloscope and they are both
          - Check again the voltage drop to ground which is still .410V on PPVRTC_G3H

          One thing which is not steady is the clock signal PCH_CLK32K_RTCX1, it seems to be fluctuating...

          What could I be missing here?

          I believe that resoldering a used SMC did something.
          How it interacts with PPVRTC_G3H, I am not sure but it could be linked to the CPU since it is not connected directly to the SMC.

          That's the first time I've encountered that problem and I guess putting another SMC would confirm my thoughts...

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          • #6
            Resistance to GND on PPVRTC? not diode mode. Should be very high MOhms

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            • #7
              I almost didn't catch that he tricked me and gave me diode mode response to a resistance question. Good one.

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              • #8
                Ok, I realize now that I need to understand the difference between both measurements... my apologies

                Resistance to ground is 6k ohms, not Mohms like my other board.

                Since I assume bad caps would create a short and that I've measured that the resistance are fine... is my CPU toasted? or should I go ahead and remove all the caps on that line?

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                • #9
                  well I did remove everything on that line except the clock chip and still 5k ohms resistance to ground...

                  CPU is toasted

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                  • #10
                    Why not remove the clock chip??

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                    • #11
                      Because I did spend already 5 clock chips on that board so I believe there is 99% of chance that I couldn't screw up that much.

                      However you are right, removing it won't make any harm.

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