Force CPU fan to run full speed.

Question

Level 1

25 points

Force CPU fan to run full speed.

Hello,

1st time Mac buyer here. I just picked up a iMac G5 17" 2Ghz at the Apple Store on Saturday.

Anyway, I've got what seems to be an excessively loud fan noise when the processor is pushed. So I go to the Apple Store and let a Genius look at it. He somehow got the processor to run full speed by booting into some command line thing. The CPU fan began to run full speed and got loud. It seemed really loud to me but he told me it was normal for this computer. I'm not so sure.

I'm thinking about going to CompUSA or Fry's and try running the fans full speed there to see if it sounds like mine or not. I don't know how to do the thing to make the fans run full speed. Can anyone help me out?

THANKS!

Posted on Jul 20, 2005 7:25 PM

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Answer 1

ToBeHuman Author

Level 1

25 points

Jul 20, 2005 8:18 PM in response to ToBeHuman

Nevermind, I figured it out. You have to press Apple Option+FO.

Note that is the letter O and not the number 0.

New question. How can you tell if you have an iMac G5 rev. A or B?

Thanks.

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Answer 2

The Dude

Level 2

255 points

Jul 20, 2005 8:32 PM in response to ToBeHuman

My goodness! I tried it just to see and boy is that loud and fast! Everyone complaining should do this so they can hear a REAL loud iMac! It would eliminate 99% of the complaints.

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Answer 3

ToBeHuman Author

Level 1

25 points

Jul 20, 2005 8:37 PM in response to ToBeHuman

Okay, I just got back from CompUSA. I tried making the fans run full speed on a 17" iMac G5 2Ghz. It was quieter than my iMac! The CompUSA iMac makes a whirring air noise when it's fans are running full speed. My iMac makes a whirring noise but it also making a whining, resonating noise, when the fans are running full speed.

I guess I'll have to make a trip to the Apple store this weekend. Anyone got any suggestions on how to make them replace my Mac? I just got it this weekend and I don't think I should have to leave it with them and wait for them to replace whatever fan is making the noise. I wish they would have just taken care it yesterday and not brushed me off.

Oh, I forgot to mention my fans run full speed quite often because my bedroom is hot.

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Answer 4

dadof3

Level 4

1,675 points

Jul 20, 2005 8:40 PM in response to ToBeHuman

I believe yours must be the rev B.

But to be sure, look at the bottom side plate where the fan intake is, there you'll see a tiny eye called an "ambient light snsor"

If you have the sensor then you have Rev B

question: when do I do that key combination, during boot or what?

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Answer 5

ToBeHuman Author

Level 1

25 points

Jul 20, 2005 8:44 PM in response to ToBeHuman

To get into the command line thing press the key combination right after you turn on the might and the white sleep light comes on. Continue to hold the keys down until the command line is loaded.

My iMac has the optical sensor. It is a rev. B.

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Answer 6

rfruth

Level 3

550 points

Jul 20, 2005 9:06 PM in response to ToBeHuman

Do all the fans run at full speed after you do AppleOption+FO thing ? I don't have G5 iMac yet but will one day soon (rev B), may want all fans at full tilt boogie all the time. Or do the fans speed up under normal op if need be ?

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Answer 7

ToBeHuman Author

Level 1

25 points

Jul 20, 2005 9:11 PM in response to rfruth

The AppleCommand+FO opens some kind of command line and doesn't load Mac OS. This command line is independant of Mac OS. Some software in Mac OS controls the system's different fans and there speeds. Since the OS doesn't load when you're in this command line the system defualts and runs all fans full speed. So, entering this command line will only make the fans run full speed when you are in it. When you are in Mac OS the fans will run slowly when the computer is not doing anything and speed up depending on CPU temperature and load.

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Answer 8

Jul 21, 2005 11:57 AM in response to ToBeHuman

This is the key combination for the Open Firmware prompt. Open Firmware being the equivalent of PC Basic IO System...although OF is quite a lot more sophisticated.

As the fans are uncontrolled in this enviroment, the System Management Unit defaults to running them at full bore to prevent damage.

If you have a kernel panic or the system hangs, you will notice the same thing.

And yes...it's loud. I get a rush of air and definate fan whirring.

The quickest/loudest I've ever been able to get my fans running under the OS is about 5k rpm (air conditioning was off and I was running at 100% CPU load running a SuperDuper Clone and re-downloading entire library to iPod (13k photos plus 3.5k songs)

I wonder what full speed is in terms of RPM on the 3 fans?

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Answer 9

Jul 21, 2005 3:27 PM in response to ToBeHuman

I am having a problem with my computer overheating. My CPUHeat Widget says the temp of my computer is between 194-202, when it gets more toward 200 it generally shuts itself off. I have brought it in to a certified technician at our campus store and they claim nothing is wrong with it. I beg to differ. I was wondering if forcing the fans to run at full speed would help bring the temp down. I may also just bring my computer to compUSA and have them check it out and send it in. What should I do?

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Answer 10

dadof3

Level 4

1,675 points

Jul 21, 2005 3:34 PM in response to adidasyellow2@mac.com

If your system is in it's first year or you have AppleCare, give them a call.

Dont accept "there is nothing wrong with it"

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Answer 11

Jul 21, 2005 11:03 PM in response to ToBeHuman

If its within 14 days they are suposed to give you a new one on request. My first imac G5 was having a PSU problem the day i brought it home. Although after a few hours i fixed it, i still went back the next day and told them the situation, and that i felt if it came out of the box with a problem, i feel unsure about what could happen later. They promptly gave me a new one!

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Answer 12

ToBeHuman Author

Level 1

25 points

Jul 23, 2005 9:36 AM in response to ToBeHuman

I guess Im SOL. The computer is mostly quiet most of the time but when the fan kicks up it is intolerable, especially since the computer sits right in front of you. Ive brought it to the Genius bar and they say its normal. I was going to return it and loose the $150 on the restocking fee but I cant because I cut out the UPC from the box to send in with the iPod rebate. They wont exchange the unit for me because they say nothing is wrong. I dont see how they could have let such an irritating design out the door. This is a rev. B iMac G5 too.

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Answer 13

Jul 23, 2005 10:13 AM in response to ToBeHuman

I believe the max rpm on a Rev A 1.8 is 5600 (CPU) 3200 (System) but I am not sure on the HD (mine never really varies from 2000) I am waiting for a new power supply to correct the fan speeds. Logic board replacement fixed them for 1 week. My CPU and System fans max out whenever the CPU temp is above 140 F.

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Answer 14

Jul 23, 2005 10:36 AM in response to ToBeHuman

The fans running full speed is a fall back postion for the imac.

My question to you is how does the imac sound when you are just using it?

I am a 1st time mac user myself. I had a Toshiba pentium 2.0 notebook. My imac 17" 1.8 rev A is a lot quieter than my Toshiba notebook was. I am talking about using the computer. When the fans on the Toshiba would come on it was really loud. Also the Toshiba notebook had the same feature where the fans would race at full bore if the operating system failed to load. It did it to me once. Now that was LOUD.

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Answer 15

ToBeHuman Author

Level 1

25 points

Jul 23, 2005 10:47 AM in response to Donald Worrell

It's quiet most of the time but when the fans spin up at all there is an annoying whining noise in addition to the air whirring noise. I think there is something wrong. I went to CompUSA to compare the sounds. I booted into OpenFirmware on the 17" iMac G5 at the store and it didn't have the whining noise like mine does, but just the whirring noise.

I brought my Mac to the Apple store. They say the noise is normal. I don't think they took enough time to listen to the kind of noise it was making. The additional whining noise.

I'll probably end up going to the Apple store again and having them check it out a 2nd time when I get the chance. Hopefully they'll do something about it.

Also, I called Apple to try and get them to send me the CPU fan so that I wouldn't have to mess with the people at the store. They said they couldn't and I would have to bring it in.

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