Q: OS X Yosemite - Graphics Card Issue

Have you tried upgrading any of them to 10.10.4?  There are several fixes in that upgrade.

the 10.10.4 release notes state Apple addressed:

• Addresses an issue that prevented some external displays from functioning properly

https://support.apple.com/en-us/HT204928

if that's not going to help is there a specific app or suite of apps that are exhibiting issues?

odd, the link is a notice from Apple as to what was fixed and the quote about the external displays is from apple word for word.

Are these all the same model machine or a mix? I have several i5 and i7 iMacs I support that are mixed cards depending on what I ordered and when. Only one is on 10.10.2 (I'm on 10.10.0 and the rest are on 10.9.4) This model has a 4GB nvidia card but it's also the only one I have w/o an external LCD and I have not heard of video issues from the user at this time..

Apple has used three different manufactures for video depending on the model of the systems in their lineup. The models with Intel video share RAM with the system, generally they are on the lower end of the line, then Nvidia and AMD/ATI on the mid or higher, depending on the year and custom build options you could have either. Generally the gpu updates come with the OS updates and apple builds and QC's them outside of the vendors influence, but if you were running some tech that required Nvidia CUDA for instance (3D rendering mostly) you might find drivers outside of Apple, this is the exception, not the rule.

Is there a screen shot you can take with a camera, or if you take one with the computer does the anomaly show up? If it doesn't on the screen cap it could be hardware related, if does on the screen cap it might be software.

RColes84 wrote:

 

All of the iMacs are the same spec, which are i5 with AMD Radeon HD 6750M 512 MB graphics card.

 

The next time the issue pops up i'll take a screen shot and let you know the outcome.

There aren't any current recalls on that machine/graphics module but now that you mention what you are working with I remember several posts in the past year from users with that graphics module having problems.  All resulted in new logic boards.

Take one of the machines, if you can, to an Apple store and have the techs run their diagnostics - far better than AHT or anything we mere mortals have.  And make them run the tests more than once as the faults may pass initially.

to be clear when I mention the possibility of "hardware" in this instance I'm thinking hardware drivers or some conflict with the drivers and something else. The likelihood of a bunch of identical computers with the the same physical hardware failing is very remote I would venture since as Ralph L pointed out there are no current recalls (at least at this time), and I concur with his get them to run the test more than once if you can.

I also had big issues with 2 Macbook Pro 13" mid 2012 with Intel HD 4000 Graphic.

Both with Graphic issues after updating to Yosemite 10.10.3 And many crashes.

I tried everything  but nothing helped. After update to 10.10.4 no Problems on both MBP!

So that is not a Hardware issue, its the Software, the Graphic Driver for some

Mac Models with specific Graphic Cards.

I am glad that my issues diapered, but for some other People it persists in 10.10.4.