Greyish Smudge marks behind the glass screen.

You have to cut the sealing tape but that can be replaced with other sealing tape (I used gaffer tape http://en.wikipedia.org/wiki/File:13-01-02-inventur-wmde-blitz-06.jpg).

I know it looks frightening but it is OK.

I used simple glass cleaning fluid (spay)

Sorry for my English too :-) (not my nativ language)

Update: Well I took my screen off to install a new SSD drive in my late 2009 iMac and also to clean the screen. I have bad news. The marks did not clean off from my monitor. It seems the marks must be inside the screen or maybe dead pixels. I'm really disappointed because I love this computer and I've always stuck with Apple products. I use this computer for graphic design and grey pixels makes it difficult because I need accurate colors on my screen. Is anyone from Apple reading this thread so we can get some feedback? I can't afford a new screen. I'll attach some pics.

Preatty rude, worse than mine was...

You have to take apart the LCD unit itself, cut the silver tape etc... very-very gently. There are some good video's on YT.

Apple will not change it forget it.

But it also look very similar to mine and mine had heat problems, as I wrote as I changed the HD the marks just disappeared. (HD overheating problem)

Is it always on OR if you turn on the Mac (after a colder night) you don't see for 4-5 minutes and it comes after that? If YES than it is heat related if not and it is on when the mac is still cold inside.

You are luckier if it is like that because that COULD be cleaned.

If it is heat related that even taking apart and cleaning the LCD will not help.

Yes it is a design problem. I will never buy iMac again...

With 375,000 views and dating back to the Ark, I doubt if Apple will be following it. Why not create your own post which will be much more likely to be replied to.

Ok, yes I see the videos now and I will try that! I wish I would have seen the videos prior to me taking my monitor off the other day. Now I need to get some of that foil tape to reseal it. I'll let you know how it goes!

I used simple ducktape, I think it works (seems to work.)

The biggest challange is to separate the LCD from the outer frame..that was not easy...

I was really afraid that I broke it... but I did not...

Report back if the cleaning was succesful, I am curious, not everybody dare to make it.

You are a brave man :-)

Word of warning to anyone hastily preparing to rip the screen off - y'day I had a similar large smudgy mark that I'd never noticed before, but when I switched off, realised it was condensation behind the screen. Cleared up after a while, but flummoxed as to why it had happened - until I walked up to it five minutes ago with a cup of coffee in hand and remembered that yesterday I'd put one down right near the monitor as the usual place for it was cluttered. So coffee is now at respectable distance and all seems OK so far, fingers crossed...

Hi all,

I just picked up my 2011 27" imac from the Apple store yesterday. They replaced my screen due to these marks. After reading through these post i'm actually kinda nervous about it re-occuring. Now i am unsure if i should leave if off when im not home or just sleep (as some suggested this could be a heat issue) I also now have a desktop air purifier in the room. Hopefully that will help with the dust. I only have about 80 days left on Applecare for the machine. what are the alternatives if this happens again after the AC expires? I heard something about an Apple Quality program? Im guessing this is certainly going to happen again for these posts

thanks

You have no good recourse in terms of compelling Apple to cover it. The chances are they will refuse to cover it. In the end if you can get rid of the failing computer as it will fail.

Just noticed the dreaded smudge on the bottom left corner of my 2012 iMac. Not sure how long I've had the issue, I just happened to open Safari full screen and saw it clearly against the clean white background. I bought the iMac in the Czech Republic and luckily the law here dicates that all electronic devices must be supplied with a full 2 year warranty.

I'm tempted to hold back on making a claim though as in everyday use I don't notice the problem and the only things that run full screen are movies and tv shows which generally have dark backgrounds anyway.

However as I get towards the end of the two year period (this December) I am certainly going to be contacting Apple to discuss a repair/replacement.

I haven't read through all the posts on this topic so am not sure if the problem is likely to get worse.

I have had similar issues as those noted on these pages. i have alos noticed many other people having similar issues. My machine was not fixed and I was told that it was due to impurties in the air where the computer was kept. I was told it was due to having a Laser printer in the same room as my iMac (i never use my prither anyway).

I was unable to make them budge , the full details are on my blog link below (not sure if you are allowed to post links here, so applogies if i am not supposed to). My blog posts highlights contradictoins in Apple's arguments.

http://thebookofw.com/imac-smudged-screens-and-apples-list-of-excuses/

I then sent an email to the Apple media team in the UK with a link to my blog including a complaint about the service I got and i have had a phone call back from the local store. I am supposed to call them but at this moment i cannot get through.

I will update you on if i get mine fixed , if I do i suggest everyone who has been told to go away to try again.

If I am told that it won't be fixed then I will keep trying.

For such help as it may be, I can only tell you this. I bought Apple Care. When a similar thing happened to me, my screen was cleaned by my local Apple store without any problems. Been there, done it and have the no charge receipt to prove it.

But if you are outside of the guarantee or Apple Care limits, then I'm afraid it is at your cost.

I had a warranty the first time it happened , i have a warranty now for my repairs they are refusing to do anything.

Also they told me cleaning would make no difference

Thanks for the update. In my case there is no smoking, printing, cooking or dehumidifying going on in the same room so it will be interesting to hear what they say when I eventually contact them about it. As I say, luckily in my case the marks are hardly noticable really (i.e. on the odd occasion there is a white background in that corner), but I suppose that's not the point on something that costs this much money.

My G5 iMac developed screen discoloaration when it was 3 years old:

http://tech.kateva.org/2008/02/my-imac-screen-dark-band-at-top-of.html

My 2009 iMac 27" developed screen discoloration when it was about 3-4 years old. It's a bit different though, the blotchy dark area is most obvious when it's first powered up after being cool. It fades as the machine warms up and is usually imperceptible a few hours later.

In my case the machine was serviced last year by an authorized Apple repair shop. I don't know if the discoloration is related to the service, as we all know the iMacs are hard to repair.

I don't expect Apple to do anything (though a recall would be nice). I won't buy another iMac though. I'd like to see an SSD Mini with iMac specs and an external monitor or three. The iMac is just too problematic and too hard to fix.