Grey smokey marks behind glass on 27" iMac

Question

Does anyone know what this is, what causes it, and if it is covered under the 1 year warranty? It is getting worse and it is extremely annoying for doing any kind of graphics or design work.
http://imgur.com/a/oPM3m
It's right in the middle/right of my screen and definitely under the glass; I tried using a dry cloth to clean the screen but it did not help.
Anyone familiar with this issue?
Thanks

Answer 1

Before you assume it's the TFT screen, it could be just the iMac's protective glass that's cuasing this issue.
This maybe the dirt and smoke culprit
If it's not under AppleCare and you want to save a few bucks in repair costs, the iMac's glass can be removed for cleaning. You need to power down the iMac prior to doing and unplug prior to doing this.
The glass is held on by strong magnets as the back of the iMac's glass uses a metal framework on the back of the glass and can be removed with a little care.
There are two ways to do this.
You can use a thin flat stiff knife putty knife of rigid plastic to pry one of the top corner of the glass away from the iMac's metal frame while holding onto the whole corner of the iMac. Then just use your hands to pry if from the magnets all the way across from the top and then as you proceed down toward the bottom pull toward you to loosen the bottom then lift off. There maybe twosmall  locating pins inthe frame you need to be careful to not lose. They should come out with the frame.
Or you can use two small suction cups to remove the glass. You can use suction cups like the ones you find for hanging plant planters on a glass window of for hanging something on a glass window.
Here is an online procedure for removing the glass here.
http://www.macframes.com/install.html
or
http://www.youtube.com/watch?v=9cHMHzq5E5I
or
http://www.youtube.com/watch?v=yeAZqw-494Q&feature=related
Once removed you can repower your iMac to see if the issue went away. If it did, you know it's the glass scren that's dirty and not the TFT screen.
The protective glass can be cleaned with an amonia free glass cleaner with a microfiber cloth or with something like iKlear screen cleaner with a microfiber cloth or even a micro fibercloth wrung out well in warm water. Clean it laying the glass on something protective like a large terry towel to prevent any damage.Then power down your iMac and carefully replace the screen making sure to put the locating pins back into the metal frame, if they fell out, using the suction cups to hold it while slowly and gently putting it back in place until the glass is caught be the magnets