Mac Pro 5,1 heat problem, fan diagnostic?

Discussion in 'Mac Pro' started by martinlangley, May 30, 2019.

  1. martinlangley macrumors newbie

    Aug 7, 2012
    Hi all this one is weird. I have a Mac Pro 5,1 with dual processor tray. When There is one processor installed,
    it boots fine, I use software to slow down the fans and all is well. When I have two processors installed, together with heatsinks and memory , it boots fine PROVIDED I leave it in the freezer for twenty minutes
    and then install the tray and boot it before it warms up again. When it warms up it crashes. If I leave out cooling it in the freezer it fails to boot. Have checked the circuitry on the heatsink sensor and that is in order. The fan software gives a temperature (heatsink) for processor A of 21 C and processor B of 27 C before the system crashes. I suspect it may be a faulty heatsink fan (B) but cannot tell when it is installed in the chassis. The fact it boots at all indicates there's no problem with the processor(s) or memory or tray circuitry.

    Anybody can tell me how to test the fan when its outside the system? Apply 5 volts? where?

    Anybody got any other ideas about how to resolve this temperature issue? I'm running Snow Leopard or Yosemite depending on what I'm doing.

    Thanks in advance, you guys are the business.
  2. startergo macrumors 6502a


    Sep 20, 2018
    I believe the Apple fans are PWM controlled. If you just apply straight voltage it will spin at highest speed. I got a tester which outputs PWM not sure what current will it support though, but that will be expensive for your purposes.
    Here is a sample for 12VDC PWM 4 wire controller based on temperature ( you can heat the probe to increase the speed)
  3. martinlangley thread starter macrumors newbie

    Aug 7, 2012

    Update for all

    Have now tested both fans and heatsink sensors by swapping around and all are in order. Next step is to boot with two processors after cooling and note verbose output before crash to determine likely whereabouts or sensor fault.

    Problem now is there seem to be no messages written! Have booted successfully after cooling at 15.24 and crashed at around 15.27. Restarted system (after swapping processor card) at 15.30 and started console app. - contains no reference to previous boot! log goes straight from 2.05 (am) to 15.30 (to now)

    Anybody any idea how I can write and save useful relevant information to diagnose?

    Thanks again

  4. martinlangley thread starter macrumors newbie

    Aug 7, 2012
    Missing filese sorted, I was looking at the wrong OS instance. Have now checked the logs at the point of crash and they tell me nothing. Seems to be hardware related.

    Any ideas as to how to diagnose the processor tray?

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3 May 30, 2019