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820-3787 - Fan spins for a second.

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  • 820-3787 - Fan spins for a second.

    I have n 820-3787 with pretty minor spill damage (see pics.) There was a short on PPVIN_S5_HS_COMPUTING_ISNS at U7330. I replaced U7330 and the short is gone. Fan spins once for about a second and that's it. Magsafe light is on. Normal green to orange switch. SMC reset is normal, turns green for a few seconds.
    PPBUS_G3H: 12.56V
    PP3V42: 3.4
    PPVRTC_G3H: 3.4
    PP3V3_S5: 3.3V
    PP3V3_SUS: 3.3V
    PP3V3_S4: 0
    PP5V_S5: 5V
    PP5V_S4: 0V

    SLP_S3 and SLP_S4 are both 0V

    When I check 3V3_S4 it will start at 3.3 while fan is spinning and then slowly work it's way down to about 0.20V. Same goes for PP5V_S4. Drops down from 5V after fan stops. Not sure where to go from here. Let me know if there's any other information that would help.

  • #2

    Yeah high side CPU FET was shorted so pretty likely the CPU is dead.

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    • #3
      On the topic of shorts, I'm measuring 0.001 in diode mode on PPVCC_S0_CPU. On a 2015 15" board I'm measuring about 0.014. Is it possible I still have a short? It's always a little tricky to tell if there's a short on the CPU lines because the resistance to ground is always so low, but this seems too low.
      Last edited by bjf; 08-18-2016, 07:59 PM.

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      • #4
        Does anyone have any thoughts on this? Is this the way a CPU would go bad? Would it most likely be internally shorted? I've removed R7300, R7310 and R7320 to isolate the issue down to the PPVCC_S0_CPU line. The top left corner (with pictures above as reference) of the CPU gets hot when viewed through infrared camera when I send 1V through the PPVCC_S0_CPU line.

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