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Thread: MacPro3,1 Mysteriously Restarts

  1. #1
    Join Date
    Sep 2003
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    Default MacPro3,1 Mysteriously Restarts

    My venerable MacPro3,1 running El Capitan often suddenly shuts off to a dark gray screen, and then immediately restarts. Often, this is a double-restart, with the second following the first immediately, with nothing appearing on the display between the two. This has only occurred at, or shortly after, first booting the cold computer. Once it has run for a while, it has not (at least to date!) had this problem after running long enough to warm up. I have tried resetting the power manager and NVRAM. I even bought a new battery backup, since I knew the batteries in the old one were dead, and suspected summertime micro power failures as the culprit, yet the problem remains.

    Apple Hardware Test found nothing. This computer occasionally dual boots into Windows 10, off a separate SSD (sorry, fans; it was that or buy another computer for software needed for classes I am taking). I am currently booted into Windows 10, to see whether the problem recurs, as it would be clearly diagnostic if it occurred only under MacOS from the MacOS SSD. More news on that after Windows has had time to run, or, more likely, the computer has had time to cool completely, and then start directly into Windows.

    Years ago, I had a Beige G3 with a similar issues that was fixed by replacing bad RAM. Any chance that is the issue?

    Any idea what might cause, and how to fix, the mysterious restarts?

  2. #2
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    Sep 2003
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    Default MacPro3,1 Mysteriously Restarts -- Now at Any Time!

    I left the computer running for a few hours, and returned to find the login screen, meaning it had restarted. So, updated situation: It restarts repeatedly and frequently when booted from cold, and then occasionally after warming up.

  3. #3
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    Sep 2003
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    Default MacPro3,1 Mysteriously Restarts -- A Problem in Hardware

    After shutting the MacPro3,1 off and allowing it to cool all night, I booted it directly into Windows 10 this morning. It spontaneously restarted after only a few minutes. With the same issue occurring when booting off of different operating systems on separate SSD hard drives, it appears the problems is:

    • Not one of software
    • Not due to a bad SSD

    Must be a problem in hardware, but which hardware?

    <><><><><>

    Details:

    Upon the restart from Windows, I allowed it to boot back into MacOS. This required eight spontaneous restarts before the login screen appeared.

    Happiness:

    You gotta love journaled operating systems! They don't solve all problems, but certainly make computers far easier to troubleshoot.

  4. #4
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    At this point I would try a clean install of the OS. If that doesn't solve it then you know it's a hardware issue. I would suspect PSU or logic board given the age of the machine.

  5. #5
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    Sep 2003
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    Default MacPro3,1 Mysteriously Restarts -- Restarts Upon Being Used

    Thanks, M.Brane! Not what I had hoped to hear, but, yeah; maybe my Eternal Mac shall not last forever.

    "At this point I would try a clean install of the OS. If that doesn't solve it then you know it's a hardware issue."

    Assessing it as a hardware issue is not enough when the same issue occurs in both MacOS and Windows 10, with each operating system booted off its own, separate SSD?

    The power supply unit was replaced in the last three or four years, but could have died since. One of the SATA bays on the logic board has not worked reliably in some years, so death due to old age is not impossible.

    A NEW OBSERVATION:

    The Mac sat idle for nearly four hours, without restarting. Within a few minutes of my beginning to type the first version of this post, it restarted three times in a row. Is that diagnostic? It is worst when it is cold, better when warmed, worst under use!

  6. #6
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    Default

    I don't have much useful to add. Doing it under Winders and Mac OS both seems indicative of a hardware issue.

    USB devices have the ability to cause this, so make sure to disconnect everything and try other devices for keyboard and moose.

    Pull half your RAM. Test, swap it.
    molṑn labe'
    "I am a mortal enemy to arbitrary government and unlimited power. I am naturally very jealous for the rights and liberties of my country, and the least encroachment of those invaluable privileges is apt to make my blood boil."
--Ben Franklin

  7. #7
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    Sep 2003
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    Default MacPro3,1 Mysteriously Restarts -- Bad RAM

    Progress? Maybe! I never trust a solution until the computer has run without trouble for a few days, but…

    After pulling one matched pair of RAM sticks, the Mac booted without any spontaneous restarts. Bad RAM would be a far better problem to have than a bad motherboard or power supply. Could replace it, or run without it.

  8. #8
    Join Date
    Jan 2006
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    That sounds positive.

    When my iMac started doing something similar a few months back, it got to the point where it wouldn't even startup. Apple tech said they thought the CPU was dead. They would replace it for $650, but it's not worth replacing. A 2011 iMac won't take any further OS upgrades.

    Good luck!

  9. #9
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    Sep 2003
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    Default MacPro3,1 Mysteriously Restarts -- Solved!

    Since pulling those two RAM sticks, the spontaneous restarts have not recurred, even after reinstalling all the funky USB devices. Ran all day yesterday in MacOS. After cooling all night, booted into Windows 10 without problems, and has remained up for forty-five minutes. Not bad progress from the endless restarts of several days ago!

    I have never understood how bad RAM completely crashes a system. Why does most of the software not keep running, with just the immediately affected routines crashed? Or, when the system totally crashes, does that mean that, by chance, the bad RAM disabled a critical part of the kernel, so that every above fails in a massive cascade?

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