iMac Intel 27" EMC 2309 (Late 2009, Core 2 Duo 3.06 or 3.33 GHz) ID iMac10,1, EMC 2374 (Late 2009, Core i5 2.66 GHz or Core i7 2.8 GHz) ID iMac11,1

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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!

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Hi Mark. I'm having the same issue but I'm not understanding how TG Pro fixed your issue. Would you mind elaborating. Isn't TG Pro just for controlling the RPM's at given internal temps? Are you implying that you set the speed of the fans higher at lower temps? This sounds promising and I would love it if my issue was fixed in the same way. Thanks!

p.s. I installed an SSD a while back and am using the SSD Fan Control app to control the fan's rpms.


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2 Answers

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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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The error 4MOT/4/40000003:HDD-1244 is a HD fan error. You'll likely need to replace the fan unit and you also may need to replace the HD as it maybe also overheating as well.

Given the fact you are doing 3D work on this older system maybe a lot to do with it.

You stated it's only when you are doing 3D work the temp goes up to 90c and thats when you get the error and when the screen gets dark.

Part of the problem is when you do 3D modeling, CAD, image processing or video editing you need a lot or RAM. So when you have a system which does not offer it the system reaches out to the HD using virtual RAM for Cache or Paging (depending on the OS and App.) This can over stress a drive and in the process create a lot of heat. When the system encounters a point when the heat is to great it shuts down the display and will also give you an AHT error like what you've gotten.

Basically, the system overheated and the fan ramped up to its max but it was still too little given the amount of heat it had to deal with.

OK what to do here??

To start with you should replace the fan as its likely getting close to wearing out and it maybe unable to get to the max output. But lets look a bit deeper than the fan error...

If you have an i5 or i7 model then I would recommend maxing out the RAM to 16 or better yet 32 GB! You'll first need to make sure the systems firmware is up to date following this Apple T/N: About EFI and SMC firmware updates for Intel-based Mac computers.

Next I would either replace the HD with a SSD or better yet add in a second drive (SSD) replacing your optical drive with a 2.5" drive carrier. Here's the IFIXT guide for doing this: Installing iMac Intel 27" EMC 2309 and 2374 Dual Hard Drive. I would go with a 512 GB unit and make it your boot drive with your apps. You'll need a drive that supports SATA II (3.0 Gb/s) like this one: Samsung SSD 850 EVO. Note the Interface line clearly states SATA 6Gb/s (compatible with SATA 3Gb/s and SATA 1.5Gb/s) Make sure the drive you do get states it supports SATA II (3.0 Gb/s) otherwise look for a different drive. Note if you go with replacing your HD with a SSD you'll likely need a much bigger SSD which will be costly! Which is why a dual setup is better.

Then we'll leave the HD as your data drive. You may also want to upgrade it as well going with a 3.5" SSHD like this one: Seagate FireCuda SSHD again note the spec sheet call out SATA Transfer Rates Supported (Gb/s) with 6.0/3.0/1.5 listed. Here is the IFIXIT guide you'll need to follow: Mac Intel 27" EMC 2309 and 2374 Hard Drive Replacement and you'll need to get this: OWC In-line Digital Thermal Sensor for iMac 2009-2010 Hard Drive Upgrade to replace the needed thermal sensor the system requires to manage its heat (SMC). Remember your HD was cooking so its likely getting to the point of failure which is why I would replace it sooner Vs later.

Now the rub! While the i Series system is worth the investment the Duo Core models are not. You also have Apples constant dropping of support on the older systems so Sierra will be the last for this model as it stands now. So newer Apps may not work as they may require newer code in the OS to work.

Lastly, if you are planning on doing a lot of 3D modeling or any heavy graphics I would recommend getting a newer system which has a better processor. Maybe a 27" i7 2011 model or the newer 27" 5k model.

iMac Intel 27" EMC 2309 and 2374 Hard Drive Image


iMac Intel 27" EMC 2309 and 2374 Hard Drive Replacement



40 minutes - 2 hours

iMac Intel 27" EMC 2309 and 2374 Dual Drive Image


Installing iMac Intel 27" EMC 2309 and 2374 Dual Drive



1 - 2 hours

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