any had a shading on iMac screen like this ?

[liquorice]

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this is a 2011 iMac already had one screen change with a similar screen problem.
doesn't show up im a pixel check, but can see it in the login screen and also noticed it while watching a video.

Am due in for the DVD drive change so shall add this to the list, so thats two graphics card changes one DVD drive to be changed and it looks like another screen.
Glad I took out applecare, unfortunately it runs out the beginning of next year

 

[MrGimper]

Not sure what Apples policy is, but with all those issues are there grounds to have your machine replaced?

 

[liquorice]

I won't hold my breath for that as last time I was in all they offered was a percentage off another iMac, but my Mrs is going to take charge and should be fun

She hates Apple by the way

 

[Talarspeed]

Mine is a late 2009, and yes this scenario crept up in the middle of my screen about 5 months ago. It also seems to come and go; some days it seems faded. My iMac is out of warranty now, so I figured it is something to live with until I buy a new one next year.

Does anyone know what is causing it?

 

[Chippy99]

It's dust inside the LCD panel itself, I think you will find.

https://forums.macrumors.com/attachment.php?attachmentid=315318&d=1323315006

You can fix it yourself if you are braver than I.

https://forums.macrumors.com/threads/1101370/

 

[ATC]

I had something that looked identical to the OP's on my '09 iMac's 24" screen but it was in lower left area (when I took the picture of it, based on lighting/cam settings etc... the pic looks slightly different but in person it looks the same as the OP's - pic below).

Apple replaced the screen without any issues (during AC period) and the genius said that this was not an uncommon problem with iMacs (he'd seen it many times, said it was due to heat build-up inside that cause part of the LCD to fade). I also could mostly only see it on log-in screen or whenever the desktop was showing a plain colored background. I keep my iMac in a dust-free area and I clean it often so it wasn't dust build up that caused the heat issue.

Anyhow, that's why I don't plan to replace my iMac with another, going forward it'll have to be a desktop with standalone LCD (Mac Pro or mini).

 

[jaxhunter]

If you do take it back in have them replace the backlight board as well. The backlight board could be over- or under- volting the backlight and causing issues.

Also, make sure they clean the inside of the glass panel as well.

However, this could just as easily be caused by dust scoring the LCD panel. make sure you keep your work space as clean as possible and don't smoke around it.