iMac mid 2010 graphics issues after installing Yosemite

I have a similar problem, but in my case stripes appear in my start screen and then it proceeds to restart itself two or three times and then it appears normally, after that I can run my computer "normally", with that I mean I can't access heavy internet sites nor use any program like Illustrator nor Photoshop because when it's moment to compress the image, my computer freezes and I have to force it to shut down 😟

It looks like this:

Um...is anyone else on this thread using an after-market SSD boot drive with TRIM enabled? I was and once I disabled TRIM, my system seems much more stable. I've been running for two hours without any graphic problems and this is far and away the longest I've been able to run my iMac without graphics issues since I installed Yosemite.

My system actually stopped booting after I attempted to take it our of safe mode and this caused me to do some googling. I came across this thread on another forum and I followed the instructions on removing TRIM support: http://www.cindori.org/forums/topic/heads-up-osx-10-10-beta-no-go/

Once I followed these instructions, my iMac booted again into regular (non-safe) mode and much to my surprise, the graphics glitches that brought me here in the first place seem to have gone away.

Hi, that is the same setup as I have, TRIM enabled with Vertex 3 SSD drive, hmm maybe i should have another go at Yosemite.

Oh why did you have to say that!

256GB Samsung SSD with TRIM turned on. I am going to be so ****** if that is the problem.

My mac has a standard 1TB hard drive and is still exhibiting the problem.

I'm not using any SSD boot drive, maybe I'll just have to wait 'til Apple releases an update 😟

My SSD/TRIM theory appears to be wrong. When I woke up this morning and hit the spacebar, the block-glitching appeared all over my screen.

Oh well, I wonder if perhaps the system freeze ups I was experiencing can be attributed to the SSD/TRIM? My iMac hasn't become totally unresponsive and that's some progress. I had assumed the two problems were interrelated but maybe they aren't.

I have standard 1TB HDD. The only fix that worked for me was going back to Mavericks.

I did the same thing. It's a software issue. More specifically, it's a Yosemite software issue.

Same goes for me. I have a 27 inch mac (mid 2012) running Maverics and had no problem installing Yosemite. Then the real fun began. I immediately downloaded and tried to install Yosemite on anothe mac I own which is a mid 2009 24 inch that was running Maverics flawlessly. The install hung up and never completed. To make a very long story short, after 2 phone calls to Apple Care, trying to repair the Macintosh HD using Disc Utilities, I ended up re-formatting the hard drive, and had to recover my system using time machine. I am back to running Mavericks on that Mac and will continue till the dust settles. What a hassle! I will, as you did, install Yosemite on my new mid 2014 Mac book pro retina. Hopefully a fix will soon come out.

My plan is to wait for a Yosemite update. As soon I see the update available in my 13" MackBook Pro I will make a 200GB partition in my iMac 1TB HDD, install Yosemite in the 200GB partition and test it. If Yosemite works fine in the 200GB partition then I will install it in the Macintosh HD partition in my iMac. I'm just tired of this back and forward between Mavericks and Yosemite.

I'm also seeing jerky graphics, no screen corruption so far though. Back to normal after a reload.

Interestingly enough I was on the developer beta program and this didn't appear until after the official release which I installed over GM3.

Looks like they "fixed" something.

I am picking up mine later from the Genius bar appointment. I'll let you know whether I see these issues again.

By the way, mine also freezes up and needs to be shut down via the power button.

Please, let us know if they changed any part in your iMac.