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Mac Pro shuts down spontaneously

Same here

Early 2008 Mac Pro 8 core, 8 gigs RAM, Geforce 8800 GT, internal 3 drive RAID. Specifically, when a render is started in Media Composer or After Effects the system powers off (not a crash). Sometimes the system just freezes, even when idle. After several crashes it would not power on. Unplugged for 30 minutes and it started back up.

This is the second go round of this behavior. Replaced and rebuilt the system drive and OS. Worked fine for several months and last week it begin this shut down behavior again. Have run all hardware tests from Apple and TechTool. Nothing appears wrong. Have reset SMC and PRAM. Reseated RAM and graphics card. Computer is in a rack in a very cold machine room. Overheating is unlikely unless something is broken on the MOB.

I feel it could be graphics card, MOB or power supply. I have tried stressing the CPUs with various programs, like Chess app, Call of Duty, Quicktime exports etc. None of them cause the power off. Perhaps when Media Composer or AE start a render they hit a particular part of the GPU or MOB and it creates a power drain of some kind.
 
Be sure to check for any 'warning' red LED lights inside the case when the shutdown occurs. We had a Mac Pro in the shop with a similar issue, turned out to be a bad set of RAM. It was very intermittent.

Apple Hardware Test failed to reveal it but running memtest overnight drew the error out easily enough. Replaced the RAM...no more shutdowns. So, I would suggest a more robust hardware test than Apple's offering and let it run for a while.
 
Rustus Maximus said:
Be sure to check for any 'warning' red LED lights inside the case when the shutdown occurs. We had a Mac Pro in the shop with a similar issue, turned out to be a bad set of RAM. It was very intermittent.

Apple Hardware Test failed to reveal it but running memtest overnight drew the error out easily enough. Replaced the RAM...no more shutdowns. So, I would suggest a more robust hardware test than Apple's offering and let it run for a while.
Click to expand...

Thanks for that. Running 5 iterations of memtest overnight as I type this.
 
Memtest found no errors. Today I tried replicating the abrupt power off using the AE project that had reliably shut it down in previous tests. Today it did not shut the system down. It worked fine. Went to Media Composer and tried the render that killed it before. No problems.

Wow, this is frustrating. I can't rely on this system to work or to not work.
 
Is it complete power down or just black screen and no data to the monitor?

I had an issue recently where spontaneously the screen went black and it had the no DVi signal message. It was exrtemely frustrating and caused alot of downtime. It ended up being as simple as the graphics card main cable had worked loose.
 
Last edited:
DeeEss said:
Is it complete power down or just black screen and no data to the monitor?
Click to expand...
Power is completely off. The LED on the front is off, fans off - everything. Except that now, it won't do it. My guess is that once it has been on for a while the bad behavior will return.
 
New power supply did the trick. Has not shut off since replacement. However, some people on that Apple thread have replaced power supplies and still had issues. In that case the MOB is defective.

No good answers here. I find it very odd that the techs at the Apple store had my computer 3 separate times and it never powered off for them. It was still under Applecare. Of course the Applecare expired and I was forced to buy the power supply myself.
 
This seems to be a common issue for 2008 MPs. I bought a second hand 2008 recently to upgrade my 2006 and had the same issue. I returned it.

I can't be of much help , but i did notice two anomalies. It had 2 x 667 mhz 2Gb RAM instead of 800 mhz and there sign of scorching on the internals near the PSU.
 
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