Q: Blinking pixels on screen after Yosemite install

If its a hardware issue, it can't have been caused by Software.  If this is the case, you're seeing a coincidence more than anything else.  Hopefully we can help you all narrow this down to the actual root cause.

I can't get any screen capture of it (shift-command 3, shift command-4 and drag, shift-command 4 + space bar).

10.10 updated the firmware (boot screens changed) in my iMac though, and the issue showed up immediately after the install.  That would be one huge coincidence wouldn't it??

The firmware has not changed. The Apple Logo with the loading bar is the new Apple Logo/Spinning gear.  In the boot process this is what tells you the kernel is loading (start of the Operating System booting up, in your case, Yosemite) - you can read about this in an older kbase article here: http://support.apple.com/kb/ht2674

Theres two sides to this...  Your GPU and LCD are likely fine, and since Screen Shots can't capture it (not GPU) AND it does not happen in Safe Boot (not LCD Panel) you could be looking at a software issue.

So.... How did you update from 10.10 GM to the Public 10.10 Release?

It could be an artefact of the upgrade process?  I wonder if the issue would be resolved if you completely erase your Mac and reinstall Yosemite onto a blank HDD.  If successful, it would tell you the upgrade process from the beta program was the cause, not Yosemite itself.

You said you had a Genius Bar appointment. Do make sure you are fully backed up since they will likely want to reproduce the issue in a known-good version of Yosemite, and if they can't reproduce the issue there, your resolve will be a full erase and install.

Thanks for that info, good to know.

Upgrade path: 10.9.5 --> 10.10 (14A388a, GM candidate 1 I believe) and each GM candidate after that.  Did an OS restore to get to 14A389.  Same issue in all versions.  I am going to try a fresh install on my other internal HD (SSD and HDD inside) and see if I experience the issue.

Genius appt. is not until Thursday, will report back with further info when I have it.

Thanks again.

Great idea installing on a second drive and booting from that.  If you can't reproduce it on a fresh install, that could well be your solution.

DO post back once you know more as Pink Panther could use the information.

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.

thank you deltone for some encouraging information.

Yes definitely a good sign.  Let us know if it returns after those steps.  As for those with alternate upgrade paths, try the same thing, where possible, and let us know if the issue is resolved.  Perhaps a corrupted download caused this?

So, as the saga continues.... I finally decided to call 1-800-my-apple. After about 15-20 minutes wait, a pretty nice guy name of Zach came on. I explained that there was no way that anything other than the install of Yosemite could have been at fault. Nothing else had changed in 2-3 years, and immediately after the 10.10 install, this pixel junk started. He totally agreed that its frustrating, and time consuming. He had me shut down, and reinstall the software ( shut down, and then use the button to restart, and immediately after the chime hold command-r. So, we started the reinstall, and after about 3.75 hours the computer restarted, and as I write this, I have yet to see any funny pixel junk. REMEMBER, that my machine was clear after the reset I performed last night, so this time I'm hoping that in the am, all will look well, and stay that way. He also (admitted) said that he had fielded several calls relative to pixel funnystuff. So, no lone rangers here. The EXTRA good news: Apple gave me a 30 day phone support access because of this issue, which would lead me to believe that its bigger than most folks at apple want to admit. Mine is a mid 2011 27", so for apple to give me a free access for 30 days is tantamount to either an admission of guilt, or the product of one really cool tech! AND THEY, the TECHS, are going to give me a follow up call between 9 & 9:15 in the am to (1)-see if all is still well, and (2)-if not run tests to verify that the graphics card is OK. If you saw my earlier post, I included info relative to a series of graphics cards that were being replaced (gratis) by apple. So, its obvious that they are aware of a problem that is either a hardware issue, (probably started by the 10.10 install) or an issue with Yosemite (my thoughts!).
S-o-o-o,
if you want to try, shut off your computer, via the apple icon on your screen. Then start it up, and hold the command and the "R" key down, and a screen will pop up that has one of the four choices being "reinstall OS X." Click it, and go do something for a half an afternoon, and maybe your pixel problem will go away. ( AND, ****<> STAY AWAY!)
The best!

F

I called Apple support and they had me do the PRAM reset (at least I think that's what it was).  Seemed to help for a while.  However, I opened mail this morning and, it's back.  Not all the time, but I have noticed a definite connection to emails with moving graphics.  Specifically an OldNavy that had a "Frozen" scene - and the snowflakes were falling, DEFINITELY had BIG pixel square on the screen.  So I am surmising that there is a connection to the graphics card.  I am not a computer tech, so I don't know the correct verbiage but hopefully they (Apple) will figure this out and it will be an easy software patch. Hopefully.......

Is everybody that is experiencing this pixel problem using the Yosemite (apple) desktop backgrounds? I seem to think that this pixel spasm is occurring on some of the background desktop scenes and not others, example: On 'pink forest' I had a pixel zoo, whereas now the background is a blue ocean shot, and no problema!I'm waiting for my 9am call from apple to get into it deeper. Will post later.

F

Responding to my own post - after reading more in "red and green square dots" I found it funny (ironic) that in my previous post I described seeing the dots while looking at an OldNavy email with a "Frozen" scene (from the movie).  Will try to adjust different settings to keep my iMac warm.