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User profile for user: JamesZhangToTheMax
JamesZhangToTheMax Author
User level: Level 1
5 points

iMac 27 inch Late 2009 Random Black Screen Issue

Hi. This issue is very common with this model apparently. So here goes. I bought an iMac and installed Windows on it. After a few weeks the screen randomly switches off (this is later discovered as the backlight turning off as the screen's image (ie, Windows start menu, background, etc) are visible when a torch is shone on it in a dark room). At first, simply restarting fixed the issue. But soon, upon restart, the screen would turn on for a second and then turn off. So I cannot even get past the apple logo with a turned on screen. However for some reason, after waiting for a few hours and turning it on, the screen worked again. But after a while, this technique didn't work and the screen turned on for a second and turned off.


This was bugging me so I took my iMac apart using iFixit's guide.


I disconnected all cables and all cables that connected to the inverter otherwise known as the LED Backlight Board and reconnected them.


I reassembled the iMac back. Still it didn't work. It got further though. It didn't turn off in the first few seconds of bootup, but just after logging in to Windows.


So I took it apart again and this time firmly reconnected the power cable from inverted board to LCD display. I reassembled and rebooted. It worked.


However after a week, the screen turned black again. I think this happened because I made the screen brighter on Windows for a while.


So I did the same thing, firmly reset the powercable. But this time it didn't work. I did it several times.


So giving up I just left it for a while. However after a day or two, I started it again. It worked.


Now this issue is really confusing me and a lot of other people. What is the problem?


Recently I read a post by Motorcycle Michael who showed that when he reset the LED Connector cables on the LCD Display, the black screen problem was fixed. So I did exactly that. I cut the retainers and disconnected and reconnected the LED Cables. It didn't work. I even tried placing wedges to hold the connection in place. Still didn't work.


So I am wondering if one of the LED cable was loose and it caused the whole LED backlight to turn off. So I intentionally disconnected one of the LED cables and reassembled. It worked! It worked without a problem. Up to now, it is still working. But why? Why is it when I disconnected one of the LED Connectors, that the backlight works, but does not with two?


Right now I am trying to decide if the problem lies in the LCD Panel, Inverter, Power Supply or Logic Board.


Does anyone here have any idea or fix? I know this post is way too long, but it is a serious problem among many users.

iMac, Windows 7

Posted on Jun 15, 2014 7:18 AM

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11 replies
User profile for user: MarkusWinter
MarkusWinter
User level: Level 1
8 points

Dec 9, 2014 1:46 AM in response to MarkusWinter

Update:


My 27in iMac late 2009 could go three days without going black or black out every few seconds. I worked around it by having a hotspot in the lower right to trigger the "screen off".


It went black only once after upgrading to Yosemite in October but has not gone black at all since the upgrade to 10.10.1.on the 18th of November.


I hope it stays that way. Very happy camper :-)

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User profile for user: Captain L
Captain L
User level: Level 1
0 points

Jan 24, 2015 7:55 AM in response to MarkusWinter

SOLVED!


I had the blackscreen/blackout issue (not the backlight) after I added RAM. I had added 2 x 4Gb and kept the 2 x 2Gb in the original slots. I now had 12 Gb.

The blackout issue started shortly after this.

After reading the post (below) I took out the 2 x 4 Gb and replaced them with 2 x 2 Gb from another Mac I had lying around. This gives me 8 Gb with 4 identical DIMMS in the slots. The Black screen did not occur again, no matter how I try to recreate it changing the brightness, screensavers and/or sleep mode.

I think the RAM solution makes sense, so far working for me, problem looks solved. Try it and let us know! Thanks Sunfiresaturn!



Sunfiresaturn including Apple logo changes for feature 126 Apple image including Apple logo changes for feature 126 Apple image ends here

Jan 19, 2014 5:03 PM

Re: 27' iMac (2011) Screen turns off

in response to Ashadur

[DocumentBodyStart:b21f0b0e-bbb6-4d8f-827a-58c825f45ac6]

All of your symptoms were indentical to mine and I tried EVERYTHING to fix it.


My realization?


RAM


I have 4 slots open in my 2010 - iMac


2x2GB DDR3-10600

2x4GB DDR3-10666


For some reason, my iMac couldn't handle both together. At first I thought it was the 10666, but then tried both RAM types separately, and both work.


I guess you shouldn't pair 10600 with 10666 - or at least different ram sizes.


I am going for 4x4GB 10666 now.


I hope this helps everyone because I was losing my mind for a short while.


iMac is happy and on full brightness.


Life is good.

Edit

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User profile for user: c_ceddy
c_ceddy
User level: Level 1
14 points

May 14, 2015 6:53 AM in response to JamesZhangToTheMax

I have a similar problem that just began in May 2015. The screen goes black and I discovered if I used the keyboard command [command option eject] to put it to sleep and then held down the [command option] keys again, it wakes up.

I also discovered it appears to be related to heat and fan speed. I have HDD Fan control app installed and turned up the fan speed and the problem has improved. If i lower the fan speed under 3200 rpm the screen turns black when the temperatures rises above 35°C.

Can anyone tell me what needs to be repaired?

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iMac 27 inch Late 2009 Random Black Screen Issue

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