Q: Imac display issues following Yosemite upgrade

I Installed over Mavericks. I have seen a definite improvement since making the changes I outlined in an earlier post, with no square artifacts and no crashes in about two days. But I also had the problem in Mavericks, although it was much less severe.

The actions I outlined in a prior post seem to have eliminated the problem. It has been about four days and my iMac hasn't crashed, nor have I seen the "squares" problem.

An update on my situation.  (Late 2009 27" iMac)

It seems after installing Yosemite my graphics card did in fact go bad.  Not sure why, but I am assuming transparency, coding, etc.

From the many reboots and crashes I also had to reinstall the operating system and restore my data.  However the tech advised me not to go with Yosemite, just up to Maveriks.  Which I did based on his advice and my experience with Yosemite so far.

Cost so far for all of this = $534 + weeks of frustration

My current problem is since I downgraded to Mavericks, I can no longer access my photos in iPhoto because it was last used in the updated version in Yosemite.  So does anyone know how to resolve this?

Maybe I'm thick, but I don't understand how installing Yosemite can break the graphics card.

Yosemite uses the graphics card in a different wat than earlier OSes. (it's more demanding). What I understood is that the iMacs graphics cards weren't that great to begin with.

I had troubles too, had the card replaced and the problems were gone (for now).

Still have problems with Yosemite though. Mostly Iphoto and app related stuff.

I started having issues with the graphics card in Mavericks, and mostly in Photoshop. But they were nowhere near as bad as with Yosemite. I'm biding my time before bringing my iMac to an Apple Store.

This whole scenario takes me back to the days of the Apple Extended Keyboard, a wonderful split keyboard that I used on my Centris 610. This was right about the time Jobs left Apple. The only problem was after using the keyboard for a couple of weeks, it would start typing double and triple letters. Apple must have sent me 10 replacements and every one if them had the same defect. After a while, I was so disgusted, I went out and bought my first Windows PC. I only went back to a Mac in 2008. Now I'm faced with a defective graphics card coupled with an OS that can't play nice with the card on a machine I paid a premium price for. Mewnwhile, my Windows machine at the office JUST WORKS.

Yeah, I know, just take your iMac in and get a new graphics card. That isn't the point, though. In times when money is tight, why should my next computer be a Mac?

I don't know. Comparable Windows based computers aren't really cheaper and I wouldn't want to poke one with a stick :-)

Running into this issue as well.

I'm torn between blaming it on Yosemite vs hardware. According to logs, it really only started happening after the 6th of Dec. Sadly i'm on a 6770 vs the 6970 that was recalled, which is mildly irritating because I highly doubt ATI just happened to use a different manufacturing process for the 6970.

Anyway, debating whether to downgrade the OS or bring it in for a $151 "fix". If they put in the same card, I don't see how that will really address the issue.

Here's part of the GPURestart log:

GPURestartReportStart

------------------------

[00] AccelChannel: PM4

Currently pending command from UnknownCtx

PendingCommandTimestamp: 0x00608837, TotalDWords: 0x000000e2, GART Offset=0x00000000227f5900, stamp_idx=0, estamp=0x00608837

PendingCommandStart:

PendingCommandEnd

I ran the Apple Hardware Test and it found no issues.

Restarted and booted straight into the guest account. Left it running over night. No glitches. Fired up iPhoto, and the screen immediately started glitching. Then clicked on launchpad while it was still thinking and the UI locks. The machine still works because I can still ssh into from another machine and execute commands.

Going to try a fresh install, and if that doesn't work, will try reverting to Mavericks. Will let you guys know...

Unfortunately I was in the exact same situation and ended up just dropping the $151 to fix it and for several weeks now it's been fine. I figure by the time it breaks again (assuming they replaced with the same faulty card) it'll be time for an iMac upgrade anyway. One thing that people discovered after I had already taken my machine in for repair was that turning off the transparency setting seemed to "fix" things. It may be better to turn off that option than to downgrade to Mavericks.

I turned it off briefly and the glitches didn't go away, so I chalked it up as a failed solution, but I will try transparency turned off with a fresh reboot....although now the machine is currently logging into a black screen after I had to force a restart because the gfx crashed again.

I have been pullin my hair out since taking part in the Yosmite testing with display problems, I like you tried everything I reported problem to a

Apple in the hope that the beta updates would address the problem, but no luck so I was at the point of getting my system checked out by Apple.

I have now got rid of transparency re booted and the problem seems to have gone away. Watch this space.

I tried disabling transparency with a fresh reboot. Things looked promising for awhile. The problems would usually manifest pretty quickly, but this time they weren't.

However, I was a bit skeptical. If transparency really has anything to do with it, I suspected putting a bit more load on the GPU would recreate the problem. So I launched iPhoto, and while it was still loading, I fired up Launchpad, which causes some animation effects. Graphical glitches immediately appeared and the UI locked up soon after.

So...I just backed up my machine and am going to try reverting to Mavericks soon. If that doesn't work, then I'll opt for the GPU replacement.

Will keep you guys informed...

Further to my recent post, turning off transparency did NOT correct the problem with the display which consisted of and angled darker area at the left side of the display.

determined to see if it was software or hardware causing the problem I have used boot camp and installed Windows 7 in a partition.

There are no display problems in windows so I think it put the ball firmly in the yosemite court.

Am now contemplating whether or not to go back and install maverick and not bother with any future OS updates.

I'm now inclined to agree with you that it's Yosemite.

I cleared my drive and reinstalled Yosemite. Things are better. It hasn't crashed yet in the 2 days since I've reinstalled, and transparency is on.

I did see a little of the gfx glitches when I launched iPhoto and clicked on LaunchPad (that combo would almost always lock up the system on my previous install). But no crash.

I also ran the stress tests in GpuTest from http://www.geeks3d.com/gputest/ and it ran them without a hitch. I'm going to try launching iPhoto while the stress test is running and see what happens. I'll edit in my findings.