iMac Intel 27". EMC 2309 (Late 2009, Core 2 Duo 3.06 or 3.33 GHz), EMC 2374 (Late 2009, Core i5 2.66 GHz or Core i7 2.8 GHz)

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Screen randomly goes black 27" iMac late 2009

HI everyone

I have a late 2009 iMac 27"

I have been experiencing a random black screen I have already done a bit research to find a fix for the issue.

  • I have done the PRAM reset but no luck.
  • I have also done the torch test and I can see the screen in the background, so can I presume it's not the logic board?

I have seen a lot of talk about replacing the inverter board is this something that can be replaced easily? And does anyone know where I can purchase one within the UK.

Any helpful advice would be gratefully appreciated.

PS: I'm doing a test on the brightness currently running at 4 to see if it goes off.

Thanks Mark

Update (02/04/2017)

Ok I thought I would post this as it's been over 2 months now,

I tried almost everything from changing the backlight and the connector to the backlight, upgrading to latest system software to cleaning the inside with air can and numerous old wive tales like changing the keyboard.

The thing that fixed it was TG Pro!

I don't understand why as I was running smcFanCntrol at the time? The only thing I do see in TG Pro pop up it states turning the computer off for a while will cool the computer this happens every time it the heatsink get's to 80 c. I have been running this software for 2 months now with no screen black out.

I am not saying this will fix all black out screens, it fixed mine and saved my investing in a new screen.

Hope this helps!

Answered! View the answer I have this problem too

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Sounds like your LED driver board is breaking down. Here's the IFIXIT guide you'll need to follow you replace it: iMac Intel 27" EMC 2309 and 2374 LED Driver Board Replacement.

But before you replace it make sure the system is fully dusted out using a soft paintbrush and can'ed air to blow away the junk. Often the dust blocks the system from cooling effectively so parts can overheat.

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Ok just waiting on some suction cups then I will give it a good dust out. Also I reduced the brightness down to 4 and it's stayed on now since my last post I don't know if that any help diagnose the issue.

Also is it best to buy a new LED Driver or a refurbished one I see a lot on ebay?

thanks Dan for the advice


To cut expenses, a used unit will be just fine here as your system is getting long in the tooth.


ok thanks Dan I will let you know how it goes.


Hi Dan

Just about to order the part, it is the LED Backlight Inverter Board?

thanks Mark


Backlight Board - Apple P/N 661-5311


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mark.mcgivern will be eternally grateful.
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