Screen sometimes doesn't come on, but mirroring works 100%

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iMac Intel 24" EMC 2267

Model A1225 / Early 2009 / 2.66, 2.93, or 3.06 GHz Core 2 Duo processor

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Isolder @isolder

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Posted: Oct 14, 2014

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Screen sometimes doesn't come on, but mirroring works 100%

I've had this iMac with the 4850 HD to the Apple Store and they claimed to have replaced just about every part from logic board to GPU.

SOMETIMES when I try to turn on the iMac the screen doesn't come on. If I plug in an external display during this time, the external display works just fine. Comes on automatically and all.

It was always my understanding that everything was linked since you can't on a working iMac disable the screen but leave external on. Apparently that's not true.

Anyway, when the screen goes into one if its "not coming on" phases it usually is fixed by unplugging the machine for a while and then plugging it back.

What the heck is going on? When the screen does come on the picture is just as great as it was the day I got the iMac. Seems like the actual LCD is working fine. SOME component in the chain must be broke, but what?

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originalmachead @originalmachead Rep: 116.3k 66 68 359 · Answer 1 · 2014-10-14T17:42:46-07:00

Help us help you. The more complete the description of your problem is (what OS are you using -there's a lot of those and some have definite sleep "issues", some history of when this started happening would help too) the more assistance we can provide, and, the sooner we can provide it.

Sounds to me like you might be having a sleep or wake from sleep issue (software). We generally don't do software problems... but I have a few ideas that may work.

Try this - change your energy saver settings (at least to test this) to uncheck put hard disk to sleep and also change the Computer sleep and Display Sleep times to never.

Try that for a few days and see if there's an improvement.

You may need a new backup battery (aka cmoss battery) this keeps the display settings when the machine is powered off. Older machines that need new batteries "forget" display info.

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