Unable to adjust backlight in target display mode

Hi. I am using my 27" iMac as a display on my windows computer and i can nolonger change the display brightness with F1/F2 on the imac keyboard.
After a bit of reading ive discovered that its a fault introduced in 10.6.8 that seems to not be addressed.
Does anyone know if a work around.
The imac is also getting rediculosly hot (unable to touch top of it) as the cpu is running 100% and the speakers do not work when in target display mode. as soon as i switch back with command+F2 cpu usage drops.
The imac is a 1st gen early 2010 model core 2 duo, 3.06ghz

I've tried rebooting, using a USB keyboard plugged into the iMac, every suggestion I can find on the forums, and every option I can think of and nothing works. Like merve0o0's, my iMac is also running very hot, but the brightness is the bigger problem for me. It was giving me a headache after a while. I even tried sunglasses.
I have found one workaround to what is pretty clearly a bug: a free app available in the Mac store called Dimmer than Dim. https://itunes.apple.com/us/app/dimmer-than-dim/id418816854?mt=12
It's a software solution, not a hardware solution, and it does compromise resolution a little because it dims the image, not the screen, but it works and makes the screen usable, at least for my needs (mostly Outlook, Excel and Powerpoint), until Apple gets around to fixing the bug.
I hope this helps.
MBA mid 2012 OSX 10.8.2, iMac 27" mid 2010 OSX 10.8.2

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Unable to control brightness in target display mode

I use my 27" mid2010 iMac as a display for my MacPro. However after the Mac OS X recent update to 10.6.8, I noticed I am unable to control the screen brightness. Usually, I was able to do so using the iMac keyboard to adjust brightness etc. but now they do not respond in Target Display Mode. The brightness adjustment do respond if I am using the iMac but not anymore in Target Display Mode. This is a little frustrating as the screen is really bright and is hurting my eyes.

Same here. Late 2009 iMac 27". This must be a bug. (Apple: please fix this, thanks!)
As a temporary solution I installed one of the brightness control apps you can find in the App store.
I used Midnight from Ollix, searching for 'brightness' in the app store reveals some more.
<note: controlling brightness this way affects colors and is no REAL fix, just makes your eyes hurt less until the bug is fixed>

No backlight in Target Display Mode on 2012 27" iMac

I am trying to use my new 2012 iMac 27" as an external display for my mid 2011 Mac Mini with Target Display Mode. At first it seems like it's not working when switching as I hit Command + F2 and the screen changes to black. But after shining a flashlight onto the monitor I can see the desktop and dock of my Mac Mini operating system. Mouse control and everything else works, it's just the backlight doesn't light up when connected to the Mac Mini. But hitting Command + F2 again brings it back to the iMac and a normal functioning backlight.
I'm assuming this is a bug in the new iMac because I had a late 2011 iMac 27" (previous generation) hooked up to this same Mac Mini and Target Display Mode worked perfectly between the two. It was even the same exact Thunderbolt cable. I have re-tested the Mac Mini and plugged it into another monitor with a DVI to Mini Display port adapter and it has worked fine. Has anybody else experienced this behavior?

HI - i had this problem too. see my previous post above. I spent weeks on the phone to apple support.
from memory:
1. I had to reinstall the OS (from a download) - but this failed to work
2. So... I had to perform a complete reinstall of the operating system (and wipe all user data)
3. and then restore all my user data.
Everything has worked seamlessly since then - which to me indicates it's a s/w problem and possibly one with something in my user profile? I just reliased I did not try and create a new user and try TDM using that. This would've proved it was a user profile problem or not.. I had one small ocassion where the screen went blank a week ago, but I just quickly pulled the TB cable out and put it back in again - and it was all ok.
So in essence I've been runing OK now since I did the reinstall and restored the user data.
Richard

15 inch early 2011 Macbook Pro to Mid 2010 27 inch Imac Target Display Mode

Hi Guys
I have a early 2011 15" Macbook Pro with thunderpolt port aswell
as a Mid 2010 27" iMac with MiniDisplay port.
I am trying to use the iMac as a second screen for my Macbook.
Both has Mountain Lion on them.
I have both Thunderbolt to Thunderbolt aswell as miniDisplay to MiniDisplay
cables.
I can't get target display mode to work.
The thunderbolt cable doesn't work at all.
The MiniDisplay does seeem to work to an extend but not completeley.
When i plug in the MiniDisplayPort cable to both machines then
the Macbook pro screen becomes blue which means secondary monitor detected.
iMac screen becomes blank. Sometimes i have enough time to see in system preferences that
the Macbook pro actually has a secondary monitor.
But just as it turned blue on the Macbook pro and black on the iMac. It turns blue again
and the iMac returns to it's Desktop.
The exact same happens when i Press Command + F2 on iMac keyboard.
Any help or ideas?

I have a 13"macbook air and a Dec. 2012 iMac 27". Out of the blue it stopped working in Target Display Mode. Switching cables doesn't help, and the iMac and MBair are connect to power. I can see the iMac screen in Share Screen mode on the MB air.
This seems to be an issue, I have encountered eg. in MacRumours:
Jan 11, 2013, 10:17 AM
#5
martinm0
macrumors 6502
Join Date: Feb 2010
I have the same issue with my 2012 27" iMac (3.4, 680MX). When I initiate Target Display mode the iMac goes black and never comes back up. On the laptop I can see the display in Display Preferences, but its as if the backlight doesn't come on in TD mode. (I even did screen sharing into the laptop and can see both displays there.
Anyway, called Apple and they determined its an issue and I have to send in for a replacement.
Anyone else with a 2012 iMac (21.5 or 27), can you please test out Target Display mode and let us know if things are working or not?

Brightness iMac in target display mode: who has it working in 10.6.8?

"With Target Display mode, you can use your iMac (27-inch, Mid 2010) or iMac (27-inch, Late 2009) with Mac OS X as an external display.": http://support.apple.com/kb/ht3924 . "Use the keyboard of the 27-inch iMac to adjust display brightness and sound volume and to control media playback of applications running on the 27-inch iMac in Target Display mode."
This used to work perfectly for me. But under 10.6.8, the brightness control stopped working. Sound and media control still work as expected. I posted before on this.
Now I know more people are experiencing this problem... I am looking for people who DO have it working under 10.6.8!
I'm looking for anything I can do to get it to work, maybe the info from people who have it working gives me some clues.
Lion is just around the corner. Please let me know if Lion fixes this problem for you.
Thanks!
Maarten

I'm using two 27" imacs and one of them is still on 10.6.8 one has been upgraded to Lion just now.
I thought it was the Lion update which caused this issue for me because I installed 10.6.8 on both of them today as well.
Now I can't adjust the brightness in target display mode on either 27" imac.... worse that that it sets it to full brightness too.
I don't know of I want to try to go back to before 10.6.8 with time machine, talk about gutted ?
can you use monitor calibration as a work around ?
I found TS3919 but it doesn't work BTW , it says to set the brigthness before entering target display mode..
Simon

Apple Mini DVI to DVI Adapter to connect Win7 tower to iMac / Target Display Mode

I currently run Windows on bootcamp on the iMac (Mid-2011), although the tasks I perform (3D modelling, rendering and such) cause the Mac to get very hot, and as a result hae a slight burn mark on the LED LCD screen.
I am buying a Windows machine, and am to uninstall bootcamp and use the Mac purely for OSX, but use the iMac screen as a monitor for the tower using Target Display Mode. My issue is - the Windows 7 tower only has DVI output. And as I understand, the Mid-2011 iMac only supports Target Display Mode via a thunderbolt cable.
My question is - Will the Apple Mini DVI to DVI adapter allow me to connect the DVI-only tower to the iMac? Thanks in advance x

Oh, I should mention also that the iMac is the 27" model. Mid-2011 3.4Ghz Intel Core i7 with 4GB RAM and 1TB Harddrive. And ATI HD5450 1GB Graphics.

Can windows 8.1 in boot Camp display in target display mode on an IMac?

I have given up on Windows 7 running in Boot Camp on my 15" MacBook Pro and displaying it on my 27" IMac via thunderbolt and Target Display Mode.
The FAQ concerning Target Dsiplay Mode farily clearly says Windows 7 won't work.
But it does not say Windows 8.1 will or will not drive Target Display Mode via thunderbolt.
see: http://support.apple.com/kb/HT5219, question 29
Has anyone found that running Windows 8.1 in BootCamp on a MacBook Pro Retina mid 2012 will display via a thunderbolt cable in to Target Display Mode on a late 2013 IMac 27"?
I don't want to go to the trouble of installing Windows 8.1 and trashing my otherwise functional Windows 7 Boot Camp installation unless it is going to display properly on my late 2013 27" IMac running OSX 10.9.3 via thunderbolt.
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no, tdm doesn't work under bootcamp regardless of which windows is being used, imho i don't think it will ever work under bootcamp

TS3775 Hi I am trying to connect my mba mid 2011 with an imac 27" 2011 with target display mode tdm. When I am using a thunderbolt cable nothing will work. When I use a minidisplay cable, both screens turn blue but eventually nothing happens. What is the

Hi I am trying to connect my mba mid 2011 with an imac 27" 2011 with target display mode tdm. When I am using a thunderbolt cable nothing will work. When I use a minidisplay cable, both screens turn blue but eventually nothing happens. What is the problem

Your answer is likely in Target Display Mode: Frequently Asked Questions (FAQ) - Apple Support If you are familiar with this document, please re-read it and I suspect you may find something you either missed or are doing incorrectly.

How can I use my 27" iMac (2010) as an additional display to my Windows 7 PC (target display mode)?

So I have purchased a windows machines so that I can play all my favourite games on, and it's not so much a problem rather I have a 27" iMac that I would like to use as an additional monitor for said games.
I have had a look at this article on using the iMac as a display for another computer and things looked promising. I think I need a bit of help getting there though as I can't find definitively anything online to tell me exactly what I need. Most stuff talks about connecting other Apple computers that have mini display ports.
My PC's video card is an nVidia Geforce GTX 650 Ti that sports 2 DVI ports and a mini HDMI port (adaptor to full HDMI was included). The iMac has a mini display port. I went out and got a HDMI cable and Moshi Mini DisplayPort to HDMI Adapter (with audio) to try to use the iMac as the additional display. I connected the PC with [a generic] HDMI cable to the adaptor which ran to the iMac and went through the appropriate steps (ie. pressing CMD + F2) to initiate target display mode. Nothing happened.
I have read that other people with different situations tried an SMC reset, but this didn't work for me either.
At this stage I wanted to see if the DVI port would do anything, or perhaps looking at a particular kind of HDMI cable, but wanted to see what the community can offer up as advice.
Any assistance would be greatly appreciated.
Thank you.

Hi,
have a read here http://support.apple.com/kb/HT3924
Regards
Stefan

IMac 27" Target DIsplay Mode + Answer to Windows 7 Boot Camp Install

First, I'd like to address the handful of complaints I've come across about installing Windows 7 via Boot Camp on the new 27"iMac.
The issue of the screen going blank when almost done has an easy albeit annoying answer. Simply connect the iMac to an external display, I used a small vga lcd with the Mini DisplayPort to VGA adapter. When the iMac's screen goes black the external lcd will continue, and when Windows 7 starts up it will download the updated ATI drivers. From there alls well.
Second, my problem.
Target Display Mode is a great feature. It worked great when I first used it, and it works great now except for the fact that the Command+F2 button combination stopped working. I have to manually unplug my MacBook Pro in order to get my iMac's original screen up. At first Command+F2 would allow me to switch back and forth, and now it does nothing.
Any suggestions?

Well, the usual first things to try for a display-related issue are
Reset PRAM
http://support.apple.com/kb/HT1379
and of that does not help, reset SMC
http://support.apple.com/kb/HT1543
which is basically unplugging the iMac from power and reconnecting it following the precise procedure.
Note: After resetting PRAM, you should go to System Preferences +Startup Disk+ pane to make sure your internal drive is selected (highlighted) as the startup disk.

Target Display Mode - Connecting pre-Thunderbolt Macbook Air to Thunderbolt iMac.

I want to use Target Display Mode in order to display my late-2010 Macbook Air (pre-Thunderbolt) to a Thunderbolt-based iMac. Is there an adapter solution to connect, say, a mini display port + USB port on the MB Air to the iMac Thunderbolt port, such that TDM would work?

Depends upon the situation. Take a look at this blog:
http://blog.macsales.com/10899-target-display-mode-and-thunderbolt

Target Display Mode not working iMac 27(2012) Bootcamp to iMac 27(2013)

Hi All,
I recently purchased an iMac 27" 2013 which replaced my iMac 27" 2010.
===============
PREVIOUS SETUP
===============
(1) iMac 27" 2012 - Running Windows 8.1
(2) iMac 27" 2010 - Running OS X Mavericks
(1)+(2) were connected with a Mini-Display-Port cable.
(1) was using (2) as external display while (2) was set to Target Display Mode using CMD+F2
==============
CURRENT SETUP
==============
(1) iMac 27" 2013 - Running Windows 8.1
(2) iMac 27" 2012 - Running OS X Mavericks
(1)+(2) are connected with Thunderbolt cable.
(1) can't use (2) as external display anymore becuase CMD+F2 has no effect anymore on (2) in this scenario.
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I am aware about the support hint from Apple where they state TDM is not working under Bootcamp.
And I agree, while booted into Windows Bootcamp this machine can't serve as external display. Makes sense because TDM is baked into OS X display drivers.
Anyone had the same experience and came to a soltuion?
Thanks,
Martin

"Apple has no plans to implement a client driver for Windows since there is no Thunderbolt SW stack available for Windows like there is for Display Port."
That is a little bit funny since Gigabyte and other big companies have said that 2014 is the year that they are going to implement Thunderbolt in many motherboards.
"GIGABYTE 7 series motherboards are the very first to offer fully certified dual onboard Thunderbolt™ ports. Capable of connecting up to 12 devices plus 3 digital displays simultaneously with breathtaking data transfer speeds that can transfer 1TB of data in only five minutes, GIGABYTE Thunderbolt™ motherboards offer the fastest connection interface on the desktop PC."
Have you asked Apple about that? I dont understand why Apple is crippling Thunderbolt on their devices...

Target Display Mode iMac 27 mid 2011 with Mac Mini 2011 bootcamp

Hello,
I can't seem to use Target Display Mode with Bootcamp.
My configuration:
Imac 27" mid 2011 with osx 10.8.4
Mac Mini Server 2011 with osx 10.8.4, bootcamp 5 and Windows7
Both are connected via Apple genuine Thunderbolt cable (2m).
When I boot the Mac Mini into OSX then Target Display Mode works perfectly and I can see the osx installed on the Mac Mini on the iMac display.
However, when I reboot the Mac Mini into Bootcamp (windows7 x64) I can't put the iMac in Targt Display Mode and get to see Windows 7 on my iMac screen.
http://support.apple.com/kb/ht3924#8
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Yes, it does.
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Hello Marcel,
It sounds like you are wanting to use the iMac in Target Display mode with your PC. Target Display mode is a feature that is supported from one Mac to another Mac according to this article:
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http://support.apple.com/kb/PH14264
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Thank you for using Apple Support Communities.
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Unable to adjust backlight in target display mode

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