If you have a Late 2009 27" iMac and are having problems with those annoying problems of flickering and parts of your screen are becoming darker (On the left side primary) you may want to consider this easy guide to fix it if you run out of warranty, have no Apple Care and Apple wanted to charge you about $600 to replace your screen. You need no tools and the cost os this procedure is 0.
First Step: Be sure that you are experiencing the same symptoms
This guide is only to resolve flickering and dimming problems on you iMac screen. Primary occurring on the left side (becoming darker or with less brightness than the other side) and on Late 2009 27" iMacs but there are cases of the same problem on later computers too.
Check/Read all of these posts to know if your case is the same:
- http://www.ifixit.com/Answers/View/54068/Black+spots+on+LCD+and+dust+inside.+Is+ it+a+factory+defect
- http://www.ifixit.com/Answers/View/44672/Is+it+possible+to+replace+only+the+back light
Thanks to the findings of nicholasfromconfolens we know that the problem resides in some parts of the screen getting loose for any reason (factory problem, heat, whatever) and if you apply pressure at certain point the flickering/dimming/darking disappears. The problem is that you need to maintain that pressure all the time.
Second Step: Find the correct spot to apply pressure
Without removing the glass panel of the iMac, try to press it strong enough (but don't use excessive force or you could break it) near the bottom left part to see if the dark/flickering disappears at some point. If it does, you are lucky, your problem has easy solution and you can proceed to the next step. If not, don't despair, your glass panel may be very strong and you will need to remove it to apply pressure. Head to the next step.
Third Step: Removing the glass panel
It is recommended to use suction cups to make this task more easily but it's not mandatory, you can remove the glass with your hands. The glass panel uses magnets to get in place all around and has some flaps on the bottom part. To remove it you need to hold it from the upper right and left corners and make force towards you, once it get loose just elevate it to remove the bottom flaps from its holes. You can follow these links with guides that clarifies this a bit more:
- http://www.ifixit.com/Guide/Installing-iMac-Intel-27-Inch-EMC-2429-Glass-Panel/7 550/1#.T-CZryt1Bcg
Fourth Step: Pinpoint the correct spot to press and place something to maintain the pressure
Once the glass panel has been removed, you must find where is the best point to apply pressure to get rid of the dimming/darking/flickering. The most common point is the left side between the rubber band of the screen and the grey band below. (See the photos for better understanding).
Once you find the best spot, you need to place there something to increase the thickness in that point and to maintain pressure when the glass panel is mounted again. I suggest you to use a pair of adhesive strips/pads mounted one over the other made of rubber or textile material that are used to put under furniture (chairs, tables) to prevent them to scratch the floor (I don't know the exact name in English, sorry).
Fifth Step: Mount the glass panel again
Mount the glass panel again and see if the pressure is enough to prevent the problem appearing again. If not, you should dismount the glass panel again and add more thickness to the "critical" spot adding more pads, but beware, add them gradually or the pressure may be excessive and break the glass when you remount it.
Enjoy your "new" screen and the saving of nearly $600 on repair costs.
Here below you can fin some photos and a video of my "set-up" to fix the problem.
I hope this guide helps you. Feel free to contact me if you have any questions.