iMac mid 2010 graphics issues after installing Yosemite

I have the same computer, and I appear to have a huge problem with the graphics subsystem as well.

After my iMac comes back from sleep, odd rows of small blocks appear in random areas of the screen and flicker on and off. Sometimes the problem just gets progressively worse, the computer eventually freezes and a hardware reset is required. Upon reboot, a dialogue box comes up informing me that a graphics problem has happened and asks permission to send debug information to Apple. Of course I approve the request and hence, Apple knows about this bug. Other times the problem seems to just go away after a few minutes and a reboot isn't required.

I've read on several site that there's a problem with the Radeon 5000 series drivers in Yosemite. Hopefully someone is working on a fix quickly because my iMac is now totally unreliable.

@kmdriver we have the same exact system, down to the amount of RAM.

I am experiencing the same issue here after 10.10 GM upgrade on my Mid 2010 27" iMac.

So far in Safe Boot the graphics issue does not occur. Any ideas??

10 sec video of it in action

I am also seeing this problem on my mid-2010 iMac 27inch since installing Yosemite.

For reference, mine has the ATI HD5750 1GB Graphics Card.

The two games I play are EVE Online and Borderlands 2. Both of these show a dramatic slowdown in FPS if launched after the iMac has woken from sleep. The slowdown goes away after restarting. I have tried an SMC reset but this makes no difference. Can confirm that reducing transparency makes no difference. I have done some before/after comparisons of processes in Activity Monitor. If I make sure no other apps are running before and after sleep, and in both cases Activity monitor shows virtually no load on the system - so there is no evidence of some 'rogue process' running off with CPU cycles after wake from sleep. It's almost as if the GPU remains in low-power mode after a wake from sleep - but I'm not even sure if this model of iMac has a low-power mode.

Good to know that safe-boot fixes the problem - should give us something to start looking in to.

I'm also going to setup a separate user account and see if that makes a difference.

Folks - what 'Energy Saver' settings do you all have? Apparently Safe Boot ignores your Energy Saver prefs and uses the default - so this might just be caused by a setting in that Pref panel.

Mine are: Computer Sleep: 2 hours, Display Sleep 10 minutes, Wake for network access: on , others: off

same problem for me.

I have the same problem with the same version of iMac. Apple support can you help?

Here's a picture of my screen. One time the noise was so bad all I could do was to shut down...

Update: Partitioned my internal HDD and installed a fresh copy of the public version of 10.10, which I downloaded from the App Store. Setup my user and in my short usage time this morning, it showed no evidence of the graphics issue I experienced on my other internal drive. To me, this does indicate a software issue in the upgrade process I followed. Other users on here have reported this same issue going directly from 10.9.5 to the public release though, so not sure what that means for our models of iMacs.

Next step for me before Genius appt. would be to backup all of my data, wipe my primary SSD, and reinstall a fresh copy of 10.10 and migrate my data back. I will let you know what happens.

Thanks for the update patscanlan. I called support and after trying a safe boot (shift-power button) the flickering did not happen. After regular boot it came back. Next step for me is to back up the data and bring it in for a Genius bar appointment or to do a fresh install of Yosemite, they suspect it's a software issue.

I hate it when an unforeseen software issue with a major software update creates hours and hours of work 😟

Same issue here as well. Nearly identical specs save my vid card is a 5670.

I just ordered another 8GB or RAM to see if installing that gets around the issue before I start tweaking crap I shouldn't need to be fooling around with...$90 upgrade via Crucial so not too expensive of a fix...if it works.

I really don't think this is RAM related. You can always shut down your iMac, take the RAM out, swap the chips around and put them back in. Also try resetting your PRAM.

I really think this is a software issue. Try installing 10.10 on an external drive and booting to it. If you do not experience the video issue while booted to the external, it is a software issue.

Of course it is a software issue. I reinstalled Mavericks from time machine backup this morning and everything has been working fine (thanks God). I have never experienced these displays issues neither with Lion, Mountain Lion nor Mavericks, right 8 hours after Yosemite installation I got into these issues. I'm not gonna waste more time into this so I decided to keep Mavericks in my iMac until Apple release a fix for this. I'm keeping Yosemite in my one week old 13" MacBook Pro Retina which is working perfect with Yosemite.

s1000r: That's exactly the same pattern I'm seeing on my screen...followed by the system freeze up and an eventual reboot.