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TICKET ARCHIVE -> Fan in Power Mac G5 goes crazy

davidessandro - Nov 11, 2007 - 7:54 pm

I've searched far and wide for answers to this problem. I've found other people who've had the same thing happen to them, but so far I've found no answers.

Until about a week ago I was on MacOS 10.3.9. Then I upgraded to Leopard. The problem may or may not be related to this.

Just today, when I put the computer (G5, 1.6 GHz single processor) to sleep, it seemed to go to sleep, except the fans started running loud, and louder and louder, until I finally had to unplug the computer because I thought it would explode. I've read that other people have experienced this when putting the computer to sleep.

After reading a post on this site from 2 years ago, I ran the Hardware Tool from my original OS install CD/DVD. I could not get through an extended hardware test, because part way through the disk test the fans started and kept going, I couldn't stop the test, and I had to turn the computer off. The quick test finished reported no problems, except that at the end of the quick test the fans started going crazy again, and kept going after the test had completed. They only stopped after I rebooted.

Is my computer dying? Is this related to the OS upgrade? Is there some temperature sensor inside that's fried?

Any help would be appreciated. For now I will try not putting the computer to sleep (either manually or through the Energy Saver).

Thank you!

DeltaMac - Nov 11, 2007 - 9:16 pm

Does your PowerMac actually go to sleep? The display will go into standby, and the power light on the front panel power button will start pulsing. If that light stays on steady, then you are not in sleep. The fans should normally shut completely off if the power light on the front is pulsing.

The Hardware Test on your original install disk does a partial test of the fans, so you should expect that the fans will change speed during that test, even to full speed, With at least 8 fans inside the tower, they will make a lot of noise, and move a lot of air, That's their purpose in life, you know.
The fans are hardware operated, but controlled by software. I have the exact same model PowerMac G5, and I have noticed a small change in the fan operation. The fans often will run up for a few seconds, then back down to a normal rate. It depends on the processor load, so lots of apps open, and your fans may get noisy for a short time.
Your PowerMac is around 4 years old. You could check that the main heat sink is not getting clogged by dust and lint. Open the side panel, and the inner clear panel. There's a small handle that allows you to pull the front fan assembly out (behind the memory slots), and you should look into that area right behind that fan. You may see a lot of dust, which you can blow out with a can of air.
Your PowerMac is fairly fail-safe about cooling. If a temp sensor fails, or is disconnected, the fans would run at full speed almost continually, and it doesn't sound like you have that (yet...). Also, if the system software/hardware causes the computer to stop responding - you can't move the mouse, and nothing else will work, but the power is on - the fans normally will slowly build up speed, maybe over a time of 5 to 10 minutes.
If that's what you have, try repairing your Disk Permissions - using your Disk Utility. You should also test your hard drive by booting to your installer disk (the Leopard disk will be good for this), and at the first screen, choose Disk Utility from the menus, and choose Repair Disk... Make sure your hard drive passes that test.
Hope some of this helps you.
= Dale
(too long - sorry!)

davidessandro - Nov 12, 2007 - 10:35 am

Thanks for the fast response!

I don't remember if the mac was completely asleep (with pulsing monitor power light), but the monitor was already dark when the fans started. I haven't put the machine to sleep again, but I could try to test this to see if it really does go to sleep.

I have noticed since I purchased the mac that the fans cycle on and off, depending on various conditions. This problem is definitely new and different behavior.

Also, with the hardware test, I did notice the fans turning on and off during the first "logic" test (or whatever it's called). What happens later is that either during the media (disk) test on the extended test, or later in the RAM test for the quick test, the fans turn on and never turn off, and just keep getting louder and louder, and they don't turn off when the quick test completes.

I will open up the box and check the heat sink for dust and lint. I'll also try running the disk utility.

Thanks for your help. I'll let you know how it turns out.

DeltaMac - Nov 12, 2007 - 5:46 pm

Your system power light will pulse when sleeping (that's the power button on the front of your tower) - but not necessarily the monitor power light. That depends on the monitor that you use. Not all will pulse when asleep. Any modern display should have a power light that changes from green to amber when in a sleep mode.

davidessandro - Nov 15, 2007 - 9:28 am

Thanks. I have an a Apple 20" monitor, so the power light on it also pulses when in sleep mode.

I have tried putting the machine to sleep several times, and none of these times have I had the problem. Either it's an intermittent thing, of the hardware test did something to help.

I still have not opened the box to check for xtra dust, nor run the disk utility. I'll do these today, and let you know what turns up.

Thanks again for your help.

davidessandro - Nov 16, 2007 - 8:58 pm

I received this response via e-mail, but I don't see it here in my question history, so I'll re-post it here. My apologies if this is a duplicate post:

***********

Hi there is a well known issue with Power Mac G5's and their fans appearing to overheat and lockup the system. More often than not, the system is not actually overheating, but as the fans increase slowly over time it is worth checking that part out, see my not at te end of this message regarding a piece of free-ware that will do this for you.

So far what we have found happens is, that any significant change to the OS triggers this reaction, and that by resetting the SMU/PMU/MMU or whatever it is called in your system, will often cure the problem for months on end, or until you apply another significant update.

IF you look in you computer's manual or go to Apple's support area, they will tel you exactly how to reset the SMU or whatever it is called on your system.

Not only will it more than likely fix the issue for a while (A long while), your system will probably run a lot faster.

I have had this issue with a dual G5 that ws fie until it was sent in for repair and have had this problem ever since I got the system back. IT has been returned several time to no avail, until eventually the Applecare ran out and I was not going to replace the system because of a glitch that seems to be so common, it is a wonder there has not been a major reaction amongst G5 owners, some have been lucky enough to get replacement Macs, some like myself have whittled many hours away trying more and more arcane fixes to the problem.
The resetting of the PMU/SMU/MMU came as a last resort and worked quite well. Not a complete cure, but one you can work with.

If you have the standard G5 tower, then simply open it up, remove the Fans and you should find a small button at the bottom Left side of the Motherboard. You must disconnect the Mac from all equipment bar monitor and mouse, but most essentially any Power Sources. to do this properly.
Locate te button, it is usually a small red button sometimes black in a small metal case. Just press it in with the eraser end of a pencil. Do not hold it in, a quick push is all that is needed.
Reassemble your mac. Attach the Power and off you go.
You mac may be laid out differently to mine as mine is a dual G5, but that is the only button on the motherboard you can press. Whilst you are in there, you might also want to replace the PRAM battery as it sounds like the system is getting close to the time when it will need to be done anyway, and this in itself could cure the problem.

Actually when I think about it, there is an application out there that will check the temperature of the various parts of your system, and this will let you know if the Temp sensors are down. I am sorry I cannot remember it's name, but it should be easy to locate via Google and it is free.

davidessandro - Nov 16, 2007 - 9:01 pm

I found a temperature sensor application called Temperature Monitor. I downloaded it from versiontracker.com.

I have not had a problem since my first post, and I've been putting the computer to sleep all the time. I'll try the SMU reset fix. Instructions for that for G5s are here:

http://docs.info.apple.com/article.html?artnum=300341

I guess I have a late 2004 G5, which means the way to reset the SMU is not to open the box and press the button on the motherboard, but only to shut down the computer, unplug the power and wait 2 minutes.

I'll give that a try.

Thanks for all the help with this!