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10.4: Fix full-speed fan issue with 10.4.4 on iMac G5s System 10.4
Tiger only hintI ran the 10.4.4 update, and my fans then went flat out. Sounded like 1800nm of thrust out the rear of my machine. Several reboots did not fix the problem. So, irst I played with pmset, and as advised in another hint here, the processor performance settings (set to highest) in the Options section of the Energy Saver System Preferences panel.

Still nothing. Another hint suggested that you zap the pram. So, I did the Command-Alt-P-R, and waited through three "Booooong!" noises. Still my fans went nuts. Then I booted a 'Linux Live' CD, and the fans were normal. Back to OS X, and it was fans-flat-out again. Okay, I then:
  1. Unplugged my machine to move it closer to the phone to call Apple support.
  2. Threatened it with advice from an annoying call centre.
  3. Booted it up.
It then worked fine. I suspect it was the unplugging that reset whatever was causing it grief. A couple of people on a European chat server had the same problem. Unplugging their machines then starting them up once it was plugged in again gave the same solution. Weird.
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10.4: Fix full-speed fan issue with 10.4.4 on iMac G5s | 13 comments | Create New Account
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10.4: Fix full-speed fan issue with 10.4.4 on iMac G5s
Authored by: mindsnare1349 on Jan 17, '06 07:33:08AM

that behaviour is present since 10.4.2 i encountered this on my iMac G5 Rev. A by using the single user mode and suddenly the fans went crazy and stay like that even after shutdowns. unplugging helped, and recently i discovered that typing "exit" in single user mode instead of "reboot" helps as well.



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10.4: Fix full-speed fan issue with 10.4.4 on iMac G5s
Authored by: siMac on Jan 17, '06 07:46:15AM

Unplugging the iMac for 20 or so seconds is in fact the official way of resetting the PMU.



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10.4: Fix full-speed fan issue with 10.4.4 on iMac G5s
Authored by: JKT on Jan 17, '06 07:56:05AM

For those that don't know, PMU = power management unit.

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PB G4, 1.5 GHz, 2x512MB RAM, 128MB VRAM, 80 GB 5400rpm HD, SuperDrive, MacOS X 10.4.3

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10.4: Fix full-speed fan issue with 10.4.4 on iMac G5s
Authored by: nicola on Jan 17, '06 08:14:02AM

Yes and no...
You may want to reset the SMU (System management unit), not [only?] the PMU, and the official way is (iMac G5 w/ambient light sensor and iMac G5 w/iSight):
- unplug the computer
- wait 10 seconds or so...
- plug the power cord while keeping the power button pressed.
- release the power button and re-press it to start as usual.

Maybe SMU == PMU, but I wouldn't take it for granted. :-)

See
<http://docs.info.apple.com/article.html?artnum=301733>
for details.



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10.4: Fix full-speed fan issue with 10.4.4 on iMac G5s
Authored by: ventifact on Jan 17, '06 07:20:51PM

I too went through this with 1st rev 20". iChat with Apple Support (with two techs!) said there was nothing I could do and to "…bring it in…" PMU buttons and the power cord/switch fix were listed for newer iSight/iMacs so I tried it anyways. The silence is deafining! I hope Apple Support reads macosxhints.



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10.4: Fix full-speed fan issue with 10.4.4 on iMac G5s
Authored by: jeaginsky on Jan 17, '06 09:27:41AM

i had the exact same probs and ended up going as far as taking it in to applecare only to be baffled by a perfectly working iMac upon arrival.
after some googling, it seems that this unit (at least the rev A) has some known issues with the logic board and incorporated midplane, and single user mode will often induce the jet engine fans.

unplug for 0:20+ and should indeed disappear.



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10.4: Fix full-speed fan issue with 10.4.4 on iMac G5s
Authored by: mm2270 on Jan 17, '06 10:12:07AM

I could be wrong, but I really don't think the jet engine fans has anything to do with being caused by single user mode, unless you're saying that the fans were still revving after booting back into normal multi-user OS X mode.

As I understand it, the fan speeds are regulated by a combination of software in the system and hardware monitoring. This is true for G5 towers as well. Since booting into single user mode puts you in a state where the software component is unable to monitor the drive and cpu temps among others, the fans go into high speed to protect the system. It's designed this way on purpose.

I've seen systems that locked up overnight and when coming in the next morning, the fans are going full tilt! Sounds like the space shuttle taking off. It does this because the system is frozen and can't communicate with the hardware (fans) to tell them how fast they should be spinning. So the built-in protection gradually kicks in and the fans rev higher and higher until they are deafening.

At least this is my understanding. If someone knows better, please tell.



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10.4: Fix full-speed fan issue with 10.4.4 on iMac G5s
Authored by: mindsnare1349 on Jan 17, '06 12:33:55PM

single user mode does not necessarily make the fans go wild. well, actually it does since 10.4.2... but it definately didnt before.



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10.4: Fix full-speed fan issue with 10.4.4 on iMac G5s
Authored by: ballardmac on Jan 17, '06 11:24:27PM

Yes, mm2270 is pretty much right on. Recent versions of the PMG5 & IMG5 (ALS) have an advanced SMU instead of a PMU, but it serves a similar purpose.

The SMU controls the fans and regulates the speeds to run each fan. The SMU derives fan speed from sensors in each thermal zone. Some of these sensors monitor thermal only, while others monitor both thermal and power.

If the SMU does not receive an update from the operating system within two minutes, it begins to ramp up the speed of the fans to full speed. This is sort of a self-preservation function.

Follow previous steps (in previous post) to reset SMU. Remember that your date and time will be reset, unless you have enabled "Set date & time automatically" in System Preferences.



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10.4: Fix full-speed fan issue with 10.4.4 on iMac G5s
Authored by: jeffulri on Jan 17, '06 04:01:42PM

Curious. What version/distrubution of Linux are you using with our iMac G5? None of the ones I've tried work (Ubuntu, etc).



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10.4: Fix full-speed fan issue with 10.4.4 on iMac G5s
Authored by: jeffulri on Jan 17, '06 04:03:04PM

Umm, our=your. Sorry! (Grin)



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10.4: Fix full-speed fan issue with 10.4.4 on iMac G5s
Authored by: oliverlangan on Jan 18, '06 12:38:16AM

This doesn't actually work for me. I tried it, but the fan sound came back quite quickly (within 5 minutes). I am not doing much, just browsing the web and playing some music.

My fans have been going crazy ever since 10.4.3.



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Clean your machine
Authored by: kd4ttc on Mar 30, '06 06:54:21PM

I finally fixed my problem. I have had the fan noise problem on my iMac flat panel since the 10.4 install. By cleaning the vents the thing has gotten back to normal. I think that the new system had a different power curve vs fan setting and that my machine must have been marginal in heat clearance. I was afraid I would need to open the machine, but just vacuuming the top and bottom holes worked. I think I need to still open it up. I burned out a 10 year old power supply on a 6116CD a year and a half ago. Inspection showed dust on the air grates. Invisible until disassembled.

---
Steve Holland



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