Fan speeds up on mac pro when i move windows around

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Level 1

9 points

Fan speeds up on mac pro when i move windows around

I've got an Early 2008 Mac Pro which I found on Craigslist and I LOVE IT! One problem though: I got it crazy cheap because someone misdiagnosed it as having a bad logic board. After taking a look at it, i figured out that it was just a bad video card which i replaced.

Now i'm getting some weird behavior. The fans spin up very fast when it boots (which I expect is normal) and then they slow down. The weird part is that once I log into Snow Leopard it sounds nice and quite until it has to render a new webpage or I drag the window around the screen (pretty much anything that changes the image on the screen dramatically. Everytime this happens I hear a fan inside the case speed up considerably, and once I the screen is done loading the fan slows back down to quiet within 1/2 second or so.

I have a hard time believing that the fan (either case fan or graphics card, not sure which) was responding to a temperature change but cooled it down that quickly and slowed back down. Also, if the screen is continually changing (ie, commands streaming across the terminal for 5-10 seconds, the fan stays spun up the entire time the screen has activity). And if it helps, when the screen saver comes on, I don't hear the fan speed up so I don't know why it would stress the vid card to render a window but not a screen saver.

Anyone run across this before?

Thanks!

Mac Pro, a1186; 3,1; 2x2.8Ghz

Posted on Jan 26, 2013 11:01 AM

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Answer 1

The hatter

Level 9

60,980 points

Jan 26, 2013 12:06 PM in response to Jickerson

you left out some details in favor of the story of the symptoms.

Do a clean install and get it to 10.6.8 with your gpu which I assume would be the Apple ATI 5770.

Reset the SMC with hitting power on 10 secs while unplugged from a/c and nothing connected, no peripherals.

Maybe there is a RAM issue. FBDIMMs fail. Almost 90% a given over time due to heat-cold stress.

Monitor the temps closely and the RAM and get the OEM DVD to run its Apple Hardware Test, then do Rember (memtest GUI).

And yes there are threads about high fan speed; yes it is somewhat normal for fans to be high... if the system was overly warm, room is warm, etc. a system cannot cool itself once in sleep or shutdown and heat just sits inside. And the case needs to be where it will cool and fresh air (not in boxed in corner or some "computer hutch").

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Answer 2

Jickerson Author

Level 1

9 points

Feb 2, 2013 9:53 PM in response to The hatter

So i've done some tests and almost certain its the graphics card whose fan is speeding up and slowing down. I've come to this conclusion from the following observations:

1. When I visit a website that is graphically intesive (scrolls through a series of hi-res images every 2-3 seconds), the fan speeds up when switching from one image to the next, but slows down in-between)

2. I wrote a simple python script that cycles through 2 steps. First it does a lot of computations to put a load on the processor for 10-15 seconds, and then pauses for 5 seconds. I performed this cycle for 5 iterations. Under this test, the fan never sped up at all.

Is there some reason why my graphics card would be so stressed just rendering images? If it helps, my video card is the Radeon HD 2600, which is currently driving two monitors at 1680x1050 each.

My EFI driver version is 1.00.252. Is there a newer driver that would help performance?

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