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My early 2009 iMac 24 has an odd red 'ghosting' on dark screens.

Posted on 2014-07-26
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Last Modified: 2014-07-28
Photoshop mockup of issue.My early 2009 iMac is experiencing an issue with red 'ghosting' on dark and black background. Straight lines are repeated to the right 3 times and curves are sort of 'smeared'.
The problem may have been around for a little while - perhaps since I had to replace a failed hard disc and had to take the machine apart - though it's only recently started to grate on me.
What is the likely issue? And can I easily replace or upgrade the NVIDIA GeForce GT 120 256 MB that is inside the machine if that is what's causing the problem?
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Question by:Jason Bevan
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by:John Hurst
John Hurst earned 250 total points
ID: 40221797
You should be able to plug in an external monitor and determine if the external monitor has the same issue.

The cable between screen and motherboard may be incorrectly seated or somewhat loose / intermittent.
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by:Jason Bevan
ID: 40221823
Thanks for the reply.  A good check that I hadn't got around to doing. I have just ordered an adaptor from Amazon so that I can plug into another monitor.  I will do this before taking the machine apart.
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rindi earned 250 total points
ID: 40221842
Possibly when you took it apart and then assembled it again, you may have disrupted something in the cooling system. Things like that often happen if the graphic card and it's memory gets too hot.

Maybe you should take the iMac apart again, and look at all the heatsinks and fans. Maybe clean off old thermal transfer paste and apply fresh paste. Also make sure nothing blocks the airflow, particularly when you assemble it again. The problem though is often, once these effects have started, you can't get them away again without replacing the video card, as when it has been run at too high temperatures for too long, the parts get damaged.
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Author Closing Comment

by:Jason Bevan
ID: 40224046
Thanks, I used a DVI adaptor to an external monitor and the problem wasn't noticeable there.  I partially disassembled the machine and did some basic dust removal and connector wiggling. I used switch cleaner in the ribbon cable connector between the main board and screen. Reassembled and problem gone.
Thanks for your help.
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by:John Hurst
ID: 40224060
@Jason Bevan  - Thanks for the update and I was happy to help.
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