Too Much RAM causing shut down? (2008 Mac Pro)

Ron, hatter, Grant,

Thank you. I'm am thinking of taking the suggestion to bring the Machine into an Apple store (somewhat far from me).

I'm really at my wits end, as the machine is just shutting off/ down in the middle of performing any given task, and I can't figure out what it is. It seems I've tried everything and have yet to determine the problem. I still (kinda) suspect the PSU, but only because nothing else makes sense. I was able to have the machine run long enough to do a hardware diagnostic (holding down the D key at start up) after leaving it off overnight and the RAM appears to be good. After it completed the RAM diagnostic, it shut down however and I could not get it to boot to the desktop.

I've tried 2 other OSX drives, but am getting the same result. It still "runs" with all drives slid out.

Any other thoughts before I take it in? If a suggestion might prevent me from making the trip, I'd surely appreciate it 🙂

Thank you all once again.

Thanks The hatter,

heat and dust and clogged fans or fan not running as it should

- The computer is nearly dust-free as I am meticulous about cleaning.

if it were to get warm and the sensor isn't telling the fan to ramp up

- The computer is incredibly quiet, though all fans are turning (and the graphics card is operating as well)

AHT does not find all prossible RAM issues, only a few with Risers and DIMms.

- I have done other diagnostics to see if the RAM was a problem too.

- At one point, the system was most stable if I removed RAM from the Lower Riser in slots 3/4. This helped for a while, but the problem got worse. At that point I ordered new ram and it did not solve the problem. I then ordered a new Riser Card, and that did not help.

- The problem has steadily (not all at once) gotten worse... the computer would "die" more ofen, and not restart.

Which is why a cheap but quality set of $35 FBDIMMs can be useful.

- Got that

Risers are $35-70

- Replaced that

Dust does get into PSUs. Got a Dust-VAC?

- I do have a dust vac and make sure my computers are cleaned, weekly.

Dust clings to RAM and other places which reduces their ability to release heat and cool.

Location. People have mistakenly put Mac into a place where it does not circulate air adequately, not that you have.

- I agree. But this computer is in a well ventilated office, with an air-cleaner/ dust collector

GPUs. Wheher the OEM 2600 or 8800GT both are likely to give trouble or die or fan stop or soldering issue.

- I thought it might be this too, so I swapped out the video card but got the same result.

It does sound like it could be heat.

- That's what I'm thinking too.... The interior temp of the machine is 63 c when sitting at the desktop. And, it'll start up and run if I leave it alone for a long time (though it doesn't run for long)

And my feeling is that any computer like these should be on a good solid 900W UPS.

- Agreed. This has the orignal power supply

A crimped USB or bad Firewire port can cause mischief as I call it but interfere adn I saw one photo of what a fried FW port that would casue shorting out. I just had to junk an Apple $60 keyboard becasue something was not right with it.

- At the moment, I've got nothing plugged into it. Prior to this I was using all USB ports on the back and the Fireware port. I have an identical mac to this one, and since this one is not working, I have all of my USB/ FW things plugged into the back up mac. No problems with that one.

Thoughts?

Thanks The hatter,

Sorry I misunderstood "900 UPS" - well..... thought it meant PSU 🙂

I don't "think" I have an "APC or Cyberpower UPS 1000VA or higher?" (I don't really know what that is, but I'll Google er'!)

63F is too cold for my old bones as well, but I somehow tolerate it in the frozen tundra of the upper midwest USA 🙂

The CPU's are about half that temperature, whilst the case temperature is what I mentioned previously - 63c.

hatter:

I finally had time to take the computer apart and clean every single scrap of it. I had always wondered why the computer was SO quiet, and I think I found my answer: fans not running.

Just as you suspected, it is heat (at least that is what it appears to be)

So I downloaded a fan control programe and WHAM! NOT so quiet anymore! Hee hee!

Well, here is the info from the system monitoring you linked to:

The fans are running FULL out now, and I am able to restart, etc.

It looks like the CPU's are running "HOT" according to this though, eh?

hatter,

I want to publicly thank you and everyone else in this thread for helping me. You kept mentioning "heat" and I finally took a look at ALL of the fans in my Mac Pro. After taking it apart and removing that which I could and cleaning it even more thoroughly, I discovered that indeed the FRONT fans on my computer were NOT turning, and thus not cooling the CPU's correctly (at all really). This is why it kept shutting down, why it would not restart and why it would not do what it was supposed to do. I installed smcFANcontrol and this immediately solved my problem. The fans came on (blazing), I tweaked the settings a bit, performed numerous restarts and then did a stress test overnight. All clear.

Your information, insight and help has saved me a lot of time and money.

I am very, very grateful to you.