HELP! Mac Pro won't stay on!!

Discussion in 'Mac Pro' started by Ommid, Oct 4, 2011.

  1. macrumors 6502

    Oct 27, 2008
    Hi all

    My Mac has been a bit funny recently, when I put it to sleep, the morning after it is on the login screen so it has reset in the night.

    Came home today, logged on and it switched off.
    Took all the drives out thinking my SSD had died
    Came to reinstall Snow Leopard on a fresh HDD and mid install it switched off
    Switched graphics cards and it did the same
    Took 6 of 8 memory sticks out and still the same.

    It doesn't switch off when on the install disc page, but after that I can't do anything!

    I have tried PRAM and SMC reset as well as unplugging the machine and removing the battery.

    Any ideas anyone??

    Could really do with some help here please as I am quite worried! :confused:
  2. macrumors 6502a

    Oct 18, 2010
    Wirelessly posted (iPhone: Mozilla/5.0 (iPhone; U; CPU iPhone OS 4_3_5 like Mac OS X; en-us) AppleWebKit/533.17.9 (KHTML, like Gecko) Version/5.0.2 Mobile/8L1 Safari/6533.18.5)

    Sounds like something on the motherboard is overheating, probably the processors, and cutting the power ?

    Then again, are you sure your power source is stable ? Try plugging the Mac Pro somewhere else and see if it helps.
  3. thread starter macrumors 6502

    Oct 27, 2008

    I got a glimpse of all the iStat temps before shut down and all seemed fine, machine will run for hours after hours if left on the installation disc which is strange because that is SATA too
  4. macrumors 6502a

    Aug 11, 2009
    It could also be the PSU that's going on the fritz.
  5. thread starter macrumors 6502

    Oct 27, 2008
    Ok quick update.

    Installed Lion from USB. Transfer part from USB went fine.

    It then switched off midway through the SSD installation part. I caught a glimpse of a red diagnostic light on the way off so assumed a CPU problem

    Did it fine the second time. Have been stressing it for the past 15 minutes with a CPU test, a 1GB file download, a youtube video and all is running fine! CPU cores at 35c and fans are inaudible.

    This version of iStat I am running doesn't show any PSU stats.

    Please can you advise who I can test the PSU if you think this may be where the problem lies?

    Thanks a lot for all your inputs


    I also have a feeling that as soon as I try to put the machine to sleep it is going to go haywire again
  6. macrumors 6502a

    Aug 11, 2009
    A dying/corrupted power supply can result in random shut-downs/resets that don't have to occur at power peaks. This fits your scenario where it resets itself while sleeping.

    If it weren't a Mac Pro but a regular PC, you could just swap the PSU and see whether the shutdowns still occur.

    Since it's a Mac Pro and if you don't have AppleCare (anymore), I guess the only way to check the PSU is by removing it from the Mac Pro enclosure (video manuals available for different models on YouTube) and have an electrician check the components.
    A PSU isn't overly complicated, so that shouldn't be too expensive. If the electrician finds the faulty component, he should also be able to replace it.
  7. thread starter macrumors 6502

    Oct 27, 2008
    I am now seeing a flash of the over temp light after the shut down and on attempt of booting up. I can't imagine that both chips will be over temp!

  8. macrumors 6502


    Feb 10, 2011
    To test the PSU you need a GOOD DVOM (Digital Volt Ohm Meter) and the repair manual for that model of Mac Pro. The repair manual gives you the pin outs on the power connector of the PSU to check the condition of the PSU.

    If you're getting over temp lights / CPU failure lights on the logic board, you could have a bad logic board, or faulty/ corrupted firmware update. To test the RAM you need to test it in pairs, and that takes time.

    Hope this helps you.
  9. thread starter macrumors 6502

    Oct 27, 2008
    No luck, have tested all pairs.

    Have tested both video cards

    It is just switching straight off now even with no hard drives in.

  10. macrumors 6502a

    Aug 11, 2009
  11. thread starter macrumors 6502

    Oct 27, 2008
    I hope you are right!

    Don't think I can stomach it being the logic board.

    Thanks for all your help today.

    Will keep you all posted tomorrow once I have been to Apple!
  12. thread starter macrumors 6502

    Oct 27, 2008
    Worked honky dory since I made this thread.

    All of a sudden last night it switched off in Aperture and now it chimes and turns off :(
  13. thread starter macrumors 6502

    Oct 27, 2008

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