27in iMac (late 2009) ATI 4850 drivers problem in Windows 7

there are well known issues with iMac 27 (late 2009). There are heaps of threads on this issue.

basically do the following:

1. install windows 7. most people get stuck at this point, due to the windows installer not having compatible drivers for ATI Radeon HD 4850 graphic card. Which apple has a fix for. search this forum if you need help here. it involves loading certain files on a USB stick or SD card and making available during windows 7 install.
2. install bootcamp drivers that came with snow leopard. (ie version 3.0). just put in snow leopard install disc whilst in windows and let autorun find setup.exe
3. then install bootcamp drivers version 3.1
4. then go to control panel, system, device manager, display adapters. double click 'ATI Radeon HD4850', click driver. (at this stage your driver should be version 8.681.0.0. You need to downgrade driver to the version it was before bootcamp 3.1. so click update driver and put in your snow leopard installed disc again and search. you should end up with version 8.661.0.0.

hope this helps.

Thanks. I rolled back the Win7 64bit ATI driver on my iMac Quad I7 to 8.661.0.0 as you suggested and it got rid of the desktop color banding problem on 8.681.0.0

After a re-boot I re-ran Windows Experience Index hoping to see an improvement in Graphics/Desktop performance for Windows Aero, but it stayed at 4.7 (not very good, but the screen looks much better).

Gaming Graphics stayed at 6.4 (OK I suppose)

Well, rollback to 661 is is not a good solution because there's problem with the 8.661 driver too! I do it myself and my iMac run worser now.

The 8.681 had the "banding" issue (computer actually run in 16-bits colors only)

The 8.661 had the driver crashing issue (blue/pink arthefacts, then crash)

I got my brand new iMac i7 27" at work for only THREE DAYS and I'm already tired of that crap... I can figure out how get it stable running on Win7 x64. I'm a computer technician and this is the first time I got that kind of trouble with a brand new computer.

My previous work's computer was a 2.33 Ghz MacBookPro running XP Pro at first (when bought 3.5 years ago), then Win7 x32 (6 month ago) without any problem!

Hi SimmZ2008

Did you have any luck fixing the stability of wondows 7 on your mac? I'm having regular blue screens and not sure what to do. I have tried the latest catalyst 10.3 press drivers which have the mobility radeon options enabled, it did fix the problem unfortunately!

Bit gutted after spening all that money on Windows 7!

cheers

James

Well actually I'm running the 8.681 version (bundled w/ Bootcamp 3.1) and it's pretty stable. But picture quality is horrible because I'm stucked into 16-bits color mode (no 32-bits available).

I'm an Apple customer for the past 10 years and this is the first time I'm VERY disapointed of my new computer. I never had any problem running WinXP or Win7 on my good old MacBookPro C2D 2.33 Ghz!

I read somewhere on a forum someone who run driver version 8.671 on his iMac 27" RD4850HD and he says it work perfectly, but I never found a way to install the 8.671 on my iMac because Apple never release this version.

I didn't solve this problem, but I have decided to avoid it completely. I already had Win7 working well under VMWare Fusion, and just wanted another option to run Win7 natively if I wanted to.

I have removed the Boot Camp Win7 completely and will continue to run Win7 as a virtual machine.

The simulated 27" monitor drivers in Fusion work without any problems. The graphic performance is satisfactory, although not quite as good as running native.

When Apple and ATI eventually get the Win7 Boot Camp drivers working, this will all be resolved (hope?).

Oh oh oh! I think I'm on the way of a working solution! Because the actual RD4850HD GPU isn't a standalone PCIe device, nor a true ATI Mobility GPU but I think of trying to force a RD4850-Mobile-HD modified driver and it actually looking to work perfectly. I first decided to try with the 8.671 driver, so I downloaded the installer from ATI website (looking inside "Previous version" sub-section), then I use "Mobility Modder.NET" freeware to hack the driver, then I force the installation of it on my Win7 x64 and it worked! I use it for the last few hours while doing some HEAVY multimedia usage and it didn't freeze and I also lost the **** 8.681 banding effect (16-bits colors)!

I'm gonna keep you informed during the few next week but it seem to be a good working solution.

If this solution work fine, I'm gonna try to modify then force the latest version of the RD4850-Mobile-HD driver. I think there's two or three new release over the actual 8.861 Apple bundle with Bootcamp 3.1...

Well, I think I got the solution. My actual "modded" ATI Mobility RD4850HD work perfectly on Windows 7 Professionnal x64! I actually used the old 8.671 version (Catalyst 9.11) because I can't succeed to modify the new Catalyst 10.2 driver (got a "corrupted INF" error). But anyway it work perfectly right now! No more display freezing (8.661), nor bad picture quality (8.861)!

Now I begin to really like my brand new iMac! 🙂

I just received my imac i7 and I am spending the day installing everything I need - which includes windows7 64bit Pro via bootcamp. I seem to be having the display driver drop outs too.

Your solution sounds great. I wish I knew how to modd the driver you mention. I just hope Apple is reading your solution and making the necessary changes. But when they improve the 3.1 bootcamp drivers how will I know to download and run it? I will subscribe to this thread.

I just received my imac i7 and I am spending the day installing everything I need - which includes windows7 64bit Pro via bootcamp. I seem to be having the display driver drop outs too.

Your solution sounds great. I wish I knew how to modd the driver you mention. I just hope Apple is reading your solution and making the necessary changes. But when they improve the 3.1 bootcamp drivers how will I know to download and run it? I will subscribe to this thread.

The best drivers I've seen on a bootcamp Windows 7 iMac are ones that Microsoft has. Use internet explorer and do a search for "Microsoft Update Catalog" (you have to use internet explorer).

Once you are in the update catalog, search for "ATI Mobility 4850" and 2 drivers should pop up. The larger one is 64-bit, and the smaller one is 32-bit. Download and install whichever version is right for you. You may have to roll back your current drivers, but maybe not.

If it installs, Windows Update will think there is a newer version available - but it's a worse driver. So I chose to hide that optional update, its in control panel, right click on the driver when it comes up and hide it. It should should up as ATI Radeon 4850, but not mobility for some reason. It's dated about 1 week newer than the update catalog driver.

Agree with qbunnie, after many hours of trying different drivers the "MS update" site as described below installs a "working perfectly" driver version 8.641 as good as i've found... as soon as i try anything newer the banding comes back.

BANDING AND DRIVER CRASHING SOLVED:

I bought the following iMac on April 18, 2010 to run Windows 7 and Autodesk REVIT 2011.

27" iMac (Late 2009)
Intel Core i7, quad-core, 2.8GHz
8GB (4x2GB) memory
1TB Hard Drive
ATI Radeon HD 4850 512MB Display Adapter
Apple Magic Mouse
Apple Wireless Keyboard
Apple BootCamp with Windows 7 Ultimate

Installed OSX, downloaded and installed all updates.
Installed BootCamp 3.1
Installed Windows 7 Ultimate 64bit and had the problem of the black screen during install. This was solved with the fix from apple support (copy latest drivers to a flash drive and continue to install windows). This resulted in apple windows driver 8.681.0.0 and the 16 bit color with banding. Rolled back the driver to 8.661.0.0. The banding issue was solved, but then had intermittent crashing (reset of the driver) in Chrome and REVIT 2011. This driver caused yellow "dots", then lockup and generally would reset. Very disruptive to REVIT.

SOLUTION:

Went to ATI website and downloaded Catalyst 10.4, then manually installed ATI Mobility Radeon HD 4850 display driver version 8.723.0.0. This display driver has 32 bit color, does NOT exhibit the color banding and has not had screen flicker, driver resets, or crashing in any programs run so far. I use this computer only for Autodesk REVIT 2011. The ATI HD 4850 is not officially supported by Autodesk, but I am able to run REVIT 2011 with hardware acceleration and anti-aliasing with no problems. So far that has been only for one day, but was not able to go more than a few minutes with the previous drivers.

I have not run any speed benchmarks yet, but compared to my Windows 32 bit XP machine, the performance is much improved.

Hi
I have installed several times Windows 7 on my imac 27 with ATI Radeon HD 4050. I want to try what you did, downloaded the catalyst 10.4, but still don't know how to install manually 8.723.0.0 is't the one that comes with Catalyst 10.4 or do I have to roll back to another driver version like explained in other discussions?.
Please help me, I need to get working with Autocad 2010.

I struggled with this for ages, then found that for the drivers I had used a Snow Leopard DVD (a retail DVD, I think), but not the one that came with the particular iMac. If you use the disk that came packaged with the particular iMac, the drivers should work out fine, in my experience.

HTH

Adam