27' iMac (2011) Screen turns off

RAM being the culprit is less unlikely than you might think. Mavericks has a LOT of new technologies (like compressed memory) and is more demanding on the RAM than previous systems.

That he also experiences the problem under BootCamp points to a hardware problem. Not sure if Win8 is also more demanding.

It should be pointed out that there seem to be several causes of the problem:

(1) the screen really goes off (you CANNOT see a faint image when shining a light on it).

(2) The backlight goes off (you CAN still see a faint image when shining a light on it).

If you are in the second category then it could still be lots of things.

If it happens after you installed Mavericks then try to go back to an earlier version and see if this makes a difference. However given how many millions of people installed Mavericks some are bound to experience the problem shortly after upgrading anyway. If you can't go back then try other RAM (like removing third party RAM and trying the Apple RAM).

Some experience it after a hardware upgrade - the problem started for me after the harddisk was exchanged as part of the Seagate Harddisk exchange program. I suspect a pin on the video cable got bend as another user posted.

Whatever it is - write to Apple. Just venting/moaning/complaining/crying here on the forum might make you feel better, but it doesn't change anything.

But be polite in your email. Rude ones go straight to the bin.

<Email Edited By Host>

Hello, thank for your advices. I'm not moaning nor crying, I'm just here to share my experiences and help people to find a solution if anything works for me (I'll try things in the next 15 days).

I'm not sure RAM is the culprits, because like you said, I used Bootcamp windows 8,1 before upgrading to Mavericks without any trouble (with the same RAM). So if Mavericks doesn't change anything to the RAM management under bootcamp, that´s something else, like the fans which don't speed up anymore. Maybe when the fans are about to speed up, it shuts down my screen (but it doesn't prevent iTunes to play music actually).

I'll keep in touch,

Daffodil

Hello guys,

I think I might have some answers. I tried different things :

1) I downgraded from Mavericks to Mountain Lion -> black screen even sooner;

2) Test my 4x2 Go of RAM = I'm able to run the iMAc longer with 4 go of RAM than with 8go before any black screen;

3) The black screen happens when I plug a USB device;

4) The black screen happens later when I'm on low brightness;

5) The black screen began when I reinstalled the OS on the internal HDD instead of the external SSD

Now I'm pretty sur that it is related to power supply, because (if you read my previous post) I also switched to the internal drive when I upgraded to Mavericks, instead of my low power consomption external SSD. And I think it's the culprit : it's wasn't Mavericks, it was switching the installation of the OS to the internal HDD (which demand higher power supply than the 3 w thunderbolt SSD).

And I'm sur that if I manage to decrease the energy consomption of the iMac, I it should not shut off the screen anymore. Any idea ?

Daffodil

Bad news on my end. A few days ago, the iMac monitor started turning off again, with increasing frequency, until it just wouldn't come back on. Took the iMac in to the Apple Store and they said it was probably the LCD. Talked to them on the phone later that night, and it turns out replacing the LCD didn't fix the issue, so it was the logic board. Given that it was going to cost about $830 for the logic board replacement (about $730 for the part, plus labor and tax), I opted to not replace the logic board.

Anyways, hopefully this isn't the case for the rest of you guys (or if it is, you got Apple Care)!

Hello ! They did not think it could be the power supply unit ? It´s cheaper to replace...

A.

mrbofus, if the mac will switch on and you have a thunderbolt port, you can run a second display of the mac, thats what im doing.

Jah_Daffodil wrote:

Hello ! They did not think it could be the power supply unit ? It´s cheaper to replace...

A.

No, they said it was the logic board.

drunknmonk wrote:

mrbofus, if the mac will switch on and you have a thunderbolt port, you can run a second display of the mac, thats what im doing.

Yeah, an external monitor works fine. But not having the built-in display work ***** #*$&.

I still don't understand why the motherboard is fine enough for an external display, but not for the internal one. I suppose that external displays have their own power supply ?

Jah_Daffodil wrote:

I still don't understand why the motherboard is fine enough for an external display, but not for the internal one. I suppose that external displays have their own power supply ?

It's not a power supply issue. The logic board routes the video from the graphics card to the internal display. If the LCD isn't the problem and the graphics card isn't the problem, then the logic board is the problem.

If the power supply does not deliver enough power, the internal screen may go off. That would explain why reducing the brightness (and the power needs) or switching to low consumption RAM (or an external self alimented screen) would do the job for some time. My iMac goes black randomly, but also when I connect an USB device...

but surely it may as well be the logic board. Who knows...

When you connect a thunderbolt screen, the iMac boots directly on it ? You don't have any settings to do ?

A.

Jah_Daffodil wrote:

If the power supply does not deliver enough power, the internal screen may go off. That would explain why reducing the brightness (and the power needs) or switching to low consumption RAM (or an external self alimented screen) would do the job for some time. My iMac goes black randomly, but also when I connect an USB device...

but surely it may as well be the logic board. Who knows...

When you connect a thunderbolt screen, the iMac boots directly on it ? You don't have any settings to do ?

A.

Correct; with an external monitor connected via Thunderbolt, when the iMac is powered on, the external display shows an image while the iMac's internal display remains off.

Sounds like it's a video card problem.

Rather than replacing the whole logic board, try with replacing a new video card.

You might be able to save the old one by reflow the card by backing them in oven (400F for 10min).

Good luck

wchi100 wrote:

Sounds like it's a video card problem.

Rather than replacing the whole logic board, try with replacing a new video card.

You might be able to save the old one by reflow the card by backing them in oven (400F for 10min).

Good luck

It's not a video card problem, it's a logic board problem. The LCD is connected to the video card through the logic board.

correct but if the video card is faulty then the screen will be black,

it is easy to diagnose by using the internal led's.

1 = power connected

2 = power at the logicboard

3 = logicboard and grapics card GPU are communicating

4 = lcd detected