Q: 24" iMac Screen Freezes since 10.6.3 update - pls help!

https://discussions.apple.com/thread/2383288?start=660&tstart=0

Sorry for the link above. This hopefully work, Apple's editor likes to mess up a href's.

Simen - thanks very much for this link.  It seems that your solution may be a viable alternative to the "kext fix" that has been the main (and reasonably reliable) solution in this multiyear thread.  However, I see some increased risk of "bricking" the computer with your solution, since it involves flashing the firmware on the graphics card.  While it is a pain to have to use the "kext fix" in this thread's solution every time there is an OS upgrade, it does seem safer as you can't "brick" the iMac by doing so.  (You might mess up the software, but that is fixable.  Firmware, though, is another story.)

Again, thanks for offering this alternative solution.  It is much more than Apple has offered to its customers!

Daniel - I don't know if you ever tried the firmware update that you listed, but it seems not to help those with the problem described in this thread.  In fact, my iMac shows that this firmware already is installed, as the firmware number on my system is the same as what this update shows will be the number after the update.  Please let us know if you have better results, but in sum I don't think that the update at your link is the solution.  Thank you, though, for suggesting it.

aieronimo:

All I can say is that I have tried this in a lab and had no troubles. But yeah, you could brick it.

I would recommend the Linux approach, and if you want to be safe then wait with flashing the rom, instead dump it to a USB drive/harddrive. When you have the original rom you could create your own Linux live CD with autostart scripts that automatically restores the gpu with the original rom. Or you could get an live CD that has ssh as autostart and a static IP or bind your iMacs MAC address to an IP at the router and use DHCP. Then you could restore the original ROM from a remote computer.

When this recovery option is established it would be safer to try with the new firmware.

Some tips, but ofcourse, something could go wrong. The kext hacks was taking to much time/frustration, and we couldn't run 10.6.8 on them (best OS for those old machines, and one of few version that doesn't work with old kexts) so we where willing to take the risk.

jnik:

This works for iMac 24 inch, 2008: (be sure to make it right or else it will mess up the computer!)

After the 3 ATI kexts have been applied (see older posts in this thread) and the CORRECT AMD-kexts have been deleted (for 2008 iMac it is AMDSupport, AMDFramebuffer, AMD2600Controller -  remember to backup):

Open: "Terminal" in Utilities app folder

Insert this and click Enter:

sudo nano /Library/Preferences/SystemConfiguration/com.apple.Boot.plist

(If it asks for a password use your login password and click Enter)

Then insert:  kext-dev-mode=1

between: <string> </string>

Now type:  Ctrl and O (to save)

and type:  Ctrl and X to quit (to quit)

(Be sure to make it right or else it will mess up the computer!)

Restart the computer. Done.

aieronimo:

In Mavericks and previous versions of OS X the use of unsigned kexts is allowed. When Yosemite was released one of the new security features prevents unsigned kext from loading. kext-dev-mode=1 allows unsigned extensions and 32-bit extensions to load for use in the development of current OS X & legacy OS X. x86_64 is a hybrid kernel capable of running both 32/64-bit extensions/apps used at a time when OS X was transitioning from a 32-bit environment to a 64-bit environment but I'm sure it does not allow the use of unsigned extensions (any Yosemite users care to try just replace kext-dev-mode=1 with x86_64 between the string markers in boot list Reboot and see if the unsigned 10.6.2 kexts will load). Maybe the firmware on the GPUs that according to Apple's firmware update says firmware not needed or is currently up to date and the 10.6.2 kexts where originally written for a these older "vintage" Macs whose EFI booted their kernel in 32-bit. Maybe flashing the firmware of these GPUs brings the firmware up to 64-bit thus being a permanent solution for future kexts written in 64-bit . Maybe flashing the firmware is the most dangerous to attempt. However this may be the only option in the very near future. Prior to Yosemite I don't think most outside of the developer community knew of kext-dev-mode=1. With ever increasing security concerns and such a large market share I would expect Apple to prevent the use of unsigned "malicious" extensions in the near future.

Carpe diem

<Edited by Host>

I do not know DOS or Linux well enough to write a tutorial. So I challenge my fellow forum members to create an easy to follow tutorial for the masses of how to flash the correct firmware on to these affected GPUs.

Carpe Diem

The change you predicted now appears to have been made. The latest security update to 10.10.2 seems to prevent the old kexts being loaded.

I'm not sure how I can step back from this. Has anyone any other super-bright ideas?

Is this happening with everyone? I'm still holding at 10.9.5 with kext fix.

iMac (20-inch, Mid 2007)

2 GHz Intel Core 2 Duo

4 GB 667 MHz DDR2 SDRAM

ATI Radeon HD 2400 XT 128 MB

Seem to be OK with 10.10.2 at the moment. But for the three old kexts to load, I had to roll back Security Update 2015-003 (dated 19 March). In something of a panic (I was trying to finish a writing project when I distractedly applied the update), I also "took ownership" of the kexts with 

chmod -R 755 <name>.kext

chown -R root:wheel <name>.kext

Which may have been a bit over the top. Or not very clever (I'm no techie).

As I'm beginning to tire of playing this "buy a new machine" game with Apple, but would like to keep my still-roadworthy iMac as secure as possible, I also asked the makers of the graphics card for help -- with either a) a driver or b) a card upgrade solution.

No joy there. "Sorry, you need to contact your manufacturer regarding both the driver and card upgradation," said AMD Tech Support.

Dear Kext Fix Gurus:

With 10.10.3 just released, and its featuring of the official release of the new Photos application, it would be great to hear if the venerable Kext Fix continues to work (albeit with the terminal hack that has been necessary since Yosemite).  Thank you in advance for your expert guidance.

I'd love to know this too. Particularly in view of this new vulnerability in which

OS X users are urged to upgrade to Yosemite version 10.10.3 as soon as possible. Apple will not patch versions older than 10.10, reportedly due to the complexity of the fix.

Can't speak for what will happen in the longer term, but I've found that the old ATI kexts can be persuaded to load under 10.10.3 using the various Terminal commands already described. So there's a little more life in the old iMac yet.

Same old, same old as far as actual experience of updating is concerned. For a whole 20 minutes, all seemed to be OK but then got a freeze. After that, the system wouldn't load at all until ran "kext-dev-mode=1" and told it to boot in x86-64 mode. Giving "root:wheel" ownership of the ATI kexts also may have helped.

In the absence of any help from Apple, it would be great to hear from anyone out there who has the slightest real idea of why any of this works!

Thanks very much, Dmaude!

Success on 10.10.3.

Well, eventually.

From 10.9.5, installed 10.10.3, had an almost immediate freeze. Had to press power button to restart. After restarting, quickly deleted and installed the needed kexts, and ran sudo nvram boot-args=“kext-dev-mode=1” from Terminal. Tried to restart but disk activity would not stop even at black screen so I hard restarted again. Kexts did not load.

Edited the /Library/Preferences/SystemConfiguration/com.apple.Boot.plist <key>Kernel Flags</key>

    <string> </string> to <string>x86_64 </string>, tried to restart, same thing, hard restarted, and kexts did not load.

Installed kexts again, thinking that the installation failed. Tried dmaude’s routine of chmod -R 755 ATI2400Controller.kext etc. but got error chmod: ATI2400Controller.kext: No such file or directory.

Tired changing permissions on the files directly giving wheel R/W, restarted, kexts did not load.

Got rid of x86_64 and edited boot.plist, adding kext-dev-mode=1 instead. Restart again. Kexts did not load.

In System Report Extensions I saw the kexts were there but not loaded: Kext signature validation error code -67061

Finally for the 3rd time after a successful restart, edited boot.plist again, emptied the <string> </string>, like it was originally, and ran sudo nvram boot-args=“kext-dev-mode=1” again from Terminal. Entered password, restarted, and glory be, kexts loaded and all is good.

What would be wonderful is if some developer would get a Kext signing certificate from Apple so these kexts would work in future iterations of Yosemite. http://stackoverflow.com/questions/26830800/cant-sign-kext-in-mavericks-yosemite