Greyish Smudge marks behind the glass screen.

I used the windscreen sucker from my TomTom SatNav. Put it in the centre, just under the iSight and pulled gently. Glass is held by magnets and has some guide pins so it's easy to reposition it correctly - was surprised how light the glass was. While I was in there I also did the screen for good measure. Took a bit of time to make sure there were no streaks left behind so have plenty of kitchen paper towelling and a lint-free cloth handy.
Edited to add that I obviously switched off and unplugged before doing any of this!

Message was edited by: Paul_31

@Paul_31 In your case the smudges are on the glass, and yeah maybe I should try your suggestion, but what if it's (behind) the screen itself.

I mean, I had they same problems with a matte iMac, no cover glass to get dirty at all?

Paul -

thanks for the advice 🙂 - looks like I might be giving this a go.

conradzoo -

Looks very much to me like my stains are on the back of the cover glass. If this is going to be a continuous problem, I need some solution other than trips to the hardware support every 3 months, and losing a week's work every time - and having to pay for it!

Message was edited by: IanSn - afterthought

Hi conradzoo
The OP seemed to describe screen staining that was the same as I'd had so I'm only suggesting how to clean the front and back of the cover glass and the front of the LCD screen. If it's behind the screen then that's a different problem and I haven't got a clue how to fix that 🙂

I have the same problem with my Mid-2007 24" iMac.
It had got worse over the past 8 months, to the point where it has spread half way down the screen in the middle and bottom right hand corner.
Went into the local genius bar today, the guy said he had seen similar before but not with the pattern I had. They have kept it and are going to replace the LCD and he said they may also replace the glass panel too. All being done under Apple Care.

Just an update on this - I took the computer in to the Apple store. The genius took a look at it and decided to replace the LCD. He said it looked like burn marks and checked to make sure the screen saver was activated. To me it didn't look like an image burn at all. Perhaps, as others have mentioned, it was due to excessive heat. Though, I have not noticed the case getting hot. Anyway, they replaced the screen and less than 24 hours later I had the computer back. The new LCD is perfect, no light backlight leak issues, no yellowing issues, and no greyish 'burn' marks. I'm very satisfied with the service and I would suggest if you are seeing marks on the screen, bring it in to the apple store and have them check it out.

I had this with my current 2007 24: imac - I had two almost "stains" - AppleCare saved the day - I was out of he computer for almost a week BUT they replaced the screen and all has been fine for more than a year.

My 27" Core i7 iMac has this brown'ish blob in the top, middle-to-left, of the screen.

It looks exactly like some kind of burn mark...

I really hope I can get it exchanged for a new one... Though I will hate being without it for a couple of weeks!

Glad I came across this. I just today noticed a weird blemish behind my screen, 20" iMac purchased 9/07. I thought it was ON the screen at first, wiped it, and noticed it didn't go away. Looked closer, with a field of white displayed on the screen, and noticed it's indeed behind the front of the glass. This is really a let down as I use the computer a lot in full screen mode on both Photoshop and Aperture for processing photos. Oddly, or perhaps not, mine is in the lower-left of the screen...it's never hot down there. All the heat seems to be in the upper portion of the computer, so I have no idea why it's in the lower left. But regardless, it's there, and I'm now wondering what I'm supposed to do. This is way outside of warranty, but with that said, I also think it's outside of what Apple should consider acceptable. This thing isn't that old, at barely 2.5 years.

I have just found that my parents new 21.5 iMac has these greyish smudges on the upper left corner of the screen.

I am 100% sure that it is not the top of the glass because i have cleaned it and when it is turned off it looks perfect, shiny, no scratches, etc..

Restarted several times tried moving video/ images around it and it looks awful (at least to me, I guess parents haven't noticed it yet.) We have had it for about 3 months or so. I'll try to attach some pictures of how you can clearly see these blots even while booting, clearly a screen problem...

Message was edited by: rocket3500

http://i936.photobucket.com/albums/ad201/rocket3500/2010-03-03200359.jpg

http://i936.photobucket.com/albums/ad201/rocket3500/2010-03-03200404.jpg

http://i936.photobucket.com/albums/ad201/rocket3500/2010-03-03200439.jpg

I am sorry to say this, but that looks terrible. Are you going to get it diagnosed?

That is basically what I had. To be 100% sure, do the ctlshift4 screen grab thing - grab a shot of the screen area - I bet it DOESN'T show up - it is something bad behind the lcd - need to get it replaced most likely.

That is exactly what I had. Apple replace the LCD under applecare.
It would cost around £400 to replace if outside warranty.

Same problem, 27" Quad Imac. Purchased 2009, December 30th. Smudge is growing day by day, for me it is not acceptable to even consider taking off the glass myself. It is an Apple problem and Apple should resolve it. Either by taking it apart or by replacing the unit. I am pretty sure it is a manufacturing problem. The stripes are horizontal over the firs 30% of the screen (from the top) and there is a straight black line appearing on the right of the screen in a vertical position about 4cm wide.
It is 100% on the inside. As soon as I start up the machine and I get the grey apple screen with the logo it appears. Any light background shows the stains. Phoning Apple Care is a waste of time, they seem to have no clue what is wrong. They come up with outright dumb solutions like resetting the PRAM.

Machines are produced nowadays in China on the cheap and there lies the problem.

If Apple does not take care of it, I will consider throwing all Apple machines out. In the last year I have noticed that the Apple quality becomes worse by the day. I have not purchased one machine in the last two years that did not have some kind of problem. Sure, Apple normally takes care of it, but it is still a pain in the neck and every time I have to bring the machine in, wait for a week only to find out that the problems have not been resolved.

I have this same problem, i have had my 27inch imac since just before christmas i did not notice any marks until about a month ago probably due to the dark wallpaper i was using, i bought some iklear cleaning spray and have cleaned the front of the glass the back of the glass and the screen itself my marks appear to look like hand a print and it seems to be growing, look at the images below.

http://i1008.photobucket.com/albums/af202/jamesc79/imac%20problems/SAM_0161.jpg

http://i1008.photobucket.com/albums/af202/jamesc79/imac%20problems/SAM_0162.jpg

http://i1008.photobucket.com/albums/af202/jamesc79/imac%20problems/SAM_0163.jpg

Has anyone had any luck with apple replacing the screens ?