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820-3115 - Quarter Fan spin

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  • 820-3115 - Quarter Fan spin

    Minor liquid damage.

    Fan spins for a couple of seconds then repeats.


    PP5V_S3 jumps from 0.2 to something as fan goes on and off
    PP5V_S0 jumps from 0.6 to something as fan goes on and off.

    Cannot see anything on either of these lines that is suspicious.

    Diode mode PP5V_S3 0.430
    Diode mode PP5V_S0 0.389 (matches donor)

    Wanted to see if it was the S3 or the S0 causing the issue. Removed Q7860. With Q7860 removed PP5V_S3 is 5v.
    Suspected Q7860, replaced it.
    Board turned on for 30 seconds with normal fan.
    Unplugged, waited and tested again - Back to same problem, quarter fan spin.

    Vcore when quarter fan spinning is not coming on.

    Begin to suspect U7400 ?
    Appreciate any help as always.

  • #2
    Check R7402/03...

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    • #3
      Both look and measure ok (180K and 150k).

      On pin 2 (input) i get a totally steady 12.56v
      On pin 1 (both, seperatley) I get 12.33v, which jumps (very quick change on multimeter - decimal point jumps about with fan pulse)

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      • #4
        Resistance between pins 17/18 and 27/28 of the ISL6259? How do the BIOS traces look and the clock chip?

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        • #5
          Do you get a pulse at the big coils (apart the CPU ones)?
          Did you try to start in SMC bypass mode?

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          • #6
            ISL looks fine. 4ohm and 20.4ohm on the readings.

            Do get pulses at the big coils PP1V5, PP5_S3 etc. Nothing on CPU ones.

            No change in SMC bypass mode.

            Wanted to see if it was the S3 or the S0 causing the issue. Removed Q7860. With Q7860 removed PP5V_S3 is 5v.
            Suspected Q7860, replaced it.
            Board turned on for 30 seconds with normal fan.
            Unplugged, waited and tested again - Back to same problem, quarter fan spin.

            Thanks again.

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            • #7
              Resistance to ground at 5V_S0?
              Do you get again steady 5V_S3 without Q7860?

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              • #8
                resistance to ground of 5V_S0 28k

                Yes 5V_S3 is present at 5v if Q7860 is removed.

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                • #9
                  If i heat Q7860 it will boot a whole OS and run until shut off. I tried replacing Q7860 again, and all the surrounding components.

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                  • #10
                    The heat affects probably other areas of the logic board...
                    Check Q7802 and R7860/62.

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                    • #11
                      Thanks, Was just looking at Q7802. Replaced it (have already replaced R7860/62)
                      Real head scratcher.

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                      • #12
                        Fucking ultrasonic fixed it. Thanks for your help.

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