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Question: iMac 27 SMC Firmware Update : Fans at maximum speed


After the SMC Firmware update of my brand new iMac 27", the fans are running at maximum speed from startup to shutdown. I tried to reboot the SMC but without effect.

1) Do you have the same issue ?
2) Is there a way to reinstall the older SMC firmware ? If yes, how ?
3) If I reinstall my system, is there a chance that it will fix the issue ?

Thank you for your help.


iMac 27" i7

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Apr 15, 2010 8:56 AM in response to Dah•veed In response to Dah•veed

Yes, I upgraded through Software Update as usual. This firmware update was installed during a system reboot, everything goes well except that the fans never stoped. It seems that it is normal that the fans go at maximum speed during this particular update but it must stop when the update is finished.

Apr 15, 2010 8:56 AM

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Apr 15, 2010 9:29 AM in response to Mitch149 In response to Mitch149

This particular firmware update has not a lot of information with it. Do you have a way of determining that it was actually installed? You might download and try to install it manually.


Apr 15, 2010 9:29 AM

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Apr 15, 2010 2:18 PM in response to Mitch149 In response to Mitch149

I did the update this morning. The caution was that the fan would run at high speed and then return to normal. There was a moving bar when the fan ran up and at the end of the bar the fan returned to normal as promised.

You might consider giving the 800 number a call and talk to a tech.

Apr 15, 2010 2:18 PM

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Apr 17, 2010 12:54 AM in response to Mitch149 In response to Mitch149

Applied the smc firmware update and fan now sounds like a chopper lifting off. Did an smc reset, cleared pram, etc. Fans still wide open. Profiler is reporting smc version 0.0000, which is not good. Should be something like 1.49f2, which is just an example. Called Apple Tech Support. Was not pleasant. The tech talked over me, instead of listening. Apple tech said since my imac 27 was purchased over 3 months ago that he couldn't help me. Tried to sell me apple care. Total deniability about anyone but me having this problem after the smc update. Said it was coincidental. He did give me a phone # for a local apple service center though. If you are having the same fan wide open problem I am, and did not before this firmware update, trust me, it Was the update. If Apple would give access to the prior firmware, i would be thrilled! I loved it when I could stay in the same room with it! If anyone has this nut cracked, please let me know!


Apr 17, 2010 12:54 AM

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Apr 17, 2010 5:04 AM in response to kahunastudio In response to kahunastudio

The Apple warranty provides 1 year of repair or replace and 90 days of phone support. Software is not covered by the warranty.

So if you had Apple Care, you would have a three year warranty with repair or replace and 3 years of phone support.

However, if you make an appointment with an Apple Store genius, they usually will apply firmware updates and they can sort it out.

Apr 17, 2010 5:04 AM

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Apr 17, 2010 6:20 AM in response to Dah•veed In response to Dah•veed


Looks that I am not the only one !

I contacted Apple and I had to explain three times the story. They all wanted that I bring back the iMac to an Apple Store, I refused. I just asked to reflash the SMC firmware manually but they didn't know how to do this... The conclusion was that a tech will come on Monday to have a look and reflash the SMC firmware. After talking to the tech to fix the appointment, he explained me that he has no tool to reflash so Apple asked him to change the logic board. This is crazy to replace the hardware if it is just a software issue.

So in the meantime I found something interesting I would like to try. On a forum about issues with an SMC firmware with MacBook Pro, a guy explained that you can reflash the firmware manually if you extract the files needed in the update package (using Pacifist) and if you install Refit. You can have a look on the post number 25 in the link below :


First I will backup all my data with time machine and reinstall the OS in the case of something will go wrong.

I will also have to decide which file to flash because there is two files in the SMC update (k23.smc and k23f.smc). One is probably for i5 logic board and the other for i7 logic board.

If you want to try this, do it at your own risk and please report here your findings.

Apr 17, 2010 6:20 AM

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Apr 17, 2010 10:20 PM in response to Mitch149 In response to Mitch149

Let me tell you my story ... following this afternoon's running the SMC firmware update on a brand new i7, 27" iMac I purchased this past week, I ran into the same problem re fans running a maximum speed ... After an hour plus trying to fix this on my own per online instructions w/o any success, I called Apple Care for assistance - no luck, even with their assistance ... final verdict from their end: the problem (fans remaining at full strength) is most likely a "mechanical" problem. With little hesitation, an Apple Care "supervisor" authorized me to take the iMac back to the store I bought it from to ask for an exchange of a new machine ... That's exactly what I did - in a jiffy, the exchange took place!


Apr 17, 2010 10:20 PM

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Apr 18, 2010 5:23 AM in response to Mitch149 In response to Mitch149

How do you flash the SMC manually? My fans are running at 100% and my SMC version says 0.000. Interestingly, If I look st the "installed software"in the software update tab of the my mac it has TWO entries for the SMC firmware. One on 14/4/2010 with No version number against it & a second entry on 18/4/2010 with version 1.0
Gos this noise is annoying!

Apr 18, 2010 5:23 AM

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Apr 18, 2010 12:20 PM in response to davethepom In response to davethepom

Ok, but be informed that you will do this at your own risk.

First download and install Refit. It's an alternative efi for Mac OS X. Then you will have to download the SMC firmware on Apple Downloads and extract the content using Pacifist. In the package you will find 3 files, k23.smc (SMC firmware for C2D iMac late 2009), k23f.smc (SMC firmware for quadcore iMac) and SmcFlasher.efi (tool to flash the firmware). Put the firmware you need and the smcflasher in Users/yourname.

Then reboot you iMac. You will arrive on refit. Select the shell (command line icon). Then type the following :

cd Users\yourname
SmcFlasher.efi -LoadApp k23f.smc


So the fs1: identify the hard drive
cd Users\yourname is the place you put the files
SmcFlasher.efi -LoadApp k23f.smc tell the system to launch the smcflasher and apply the firmware, in this case the SMC firmware for the quadcore iMac.
Reset tell the system to reboot.

Then you can check that the version of SMC is no more 0.000 and you can uninstall refit (see the readme file).

Apr 18, 2010 12:20 PM

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Apr 18, 2010 4:48 PM in response to fmelipin In response to fmelipin

One more thing that I have noticed is that subsequent to the firmware failing to install correctly, any manual repeat of the firmware installation
comes up with an error - not compatible with this system.

Rgds pom

Apr 18, 2010 4:48 PM

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Question: iMac 27 SMC Firmware Update : Fans at maximum speed