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Draeconis

macrumors 6502a
Original poster
May 6, 2008
987
281
Hi all,

My colleagues Mac Pro Late 2013 is acting really odd. When you start it, it passes POST and you see the Apple logo and the loading bar (running 10.10.5) as you'd expect. It gets to about 1/3, then the screen glitches, the fan starts to run at about 80%, and the machine then puts itself to sleep. The screens seem to turn on and off sporadically, as if receiving a signal briefly, then not. The machine also responds to ping, but erratically, sometimes 0.2ms, sometimes around 30ms, or even up to 150ms or so.

  • We've tried resetting the SMC, no difference.
  • When we try to reset the NVRAM, instead of restarting the machine turns off.
  • Running fsck -fy from single-user mode yields nothing.
  • Booting from an alternative source (USB, NetBoot, Internet Recovery) makes no difference.
  • AHT via Internet Recovery finds no issues.
  • Visual inspection of the components doesn't reveal anything glaringly obvious that might have failed.

It's a bizarre one. I've never seen a machine act like this. Anyone have any ideas? I have a suspicion it might be a GPU issue, but I'm at a loss why the machine puts itself to sleep straight away.
 
Use the command + v keys at the same time when booting to get a verbose (text) boot then you will see where it fails in the messages that scroll by.
 
Use the command + v keys at the same time when booting to get a verbose (text) boot then you will see where it fails in the messages that scroll by.

We seem to have fixed it by reseating all the RAM. I still can't explain what it was doing though.
 
This issue has returned.

We've methodically removed all RAM, and tried the following;
  • One DIMM in Slot 1 - Mac boots but hangs before reaching the login window. Fan spins to around 50%
  • Same DIMM in Slot 2 - Mac boots, but we never see the Apple logo, machine than automatically enters Sleep without any keyboard command or button pressed to tell it to do that.
  • Tried this same DIMM on it's own in an different identical Mac Pro, and it boots fine.
Is it reasonable to assume therefore that the issue lies with the Mac Pro itself?
 
Yes I would think so and it is time as well to either get the diagnostic disk or take it to a store to get it checked by Apple.
 
AHT comes back fine, tried this one before. :/

We send stuff off to Amsys, but knowing them the machine could come back in worse condition than it left in.
 
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