my macbook pro does not detect external display anymore

Thanks for the help dotshell, but this isn't the fix I am looking for. I should be able to wake up my laptop, while it is closed, using my external keyboard and mouse, and this should wake up my external monitor as well. I know that other Apple computers can do this because my wife's Macbook Air works perfectly in this way. I shouldn't need to open up my computer at all. Thus my frustration.

I'm using this workaround, works also after 10.8 Mountain Lion update:

Launch monitor detection with "Cmd-Shift-E"

wait a few seconds

Unplug and replug the external monitor

I solved this for my Samsung SyncMaster SA350 by connecting my Monitor to a windows computer and then updated its firmware from the Samsung website. Then when I connected it back to my Macbook Pro SSD, it seemed to show up in Detect Display again, and all is well.

As a side note, working with Switch Res X and gfxCardStatus did not seem to solve the problem for me on their own. Now the the Firmware is up to date, my SynchMaster works as it should. 🙂🙂🙂

Hi Guys i too have this same issue. I am using a Mid 2010 Macbook Pro 13 inch model with 4gb ram, and using mini display port to hdmi 5 meter cable to the back of my samsung 32 " flat panel LCD TV. it used to work but has since stopped working and ive tried all the things noted here and nothing seems to work. Even with Switch res x i just give up it must be my cable from amazon cable matters!!! should i send cable back and get a replacement or what?

I've had same problem. Someday my Late 2011 Macbook Pro didn't recognize my Dell UM2312HM. Previously everything worked fine. I was connecting display via apple's mini displayport converter -> DVI. The symptoms was that screen just blinked blue once after connecting the adapter and nothing happened. On Windows via bootcamp system didnt recognize any external display. I've tried mini DP -> VGA converter, and nothing happened. I went to the computer store and tried third-party mini DP converter to DVI with their display. That didn't work. Interesting thing was, that Macbook worked well with Apple's Thunderbolt display in Apple Store, so the mini DP socket was right.

And...

I bought the cheapest non-branded mini display port -> DVI cable WITHOUT adapter and it worked!

It seems that there is a problem with apple's mini displayport -> DVI and VGA adapters. I simplyfied the connection by eliminating their adapter, now its "clean" cable without any adapters between mac and external screen via DVI. And I'm happy again with my Dell. 😉

Macbook Pro early 2010 (7.1) + apple dvi adapter + Mountain Lion + external monitor --> work`s well

Mac mini 2010 + apple dvi adapter + Mountain Lion + external monitor--> work`s well

Macbook Pro late 2011 (8.2 Thunderbolt) + Mountain Lion + apple Tunderbolt display --> work`s well

Macbook Pro late 2011 (8.2 Thunderbolt) + apple dvi adapter + Mountain Lion + external monitor ---> didn't recognize

Macbook Pro late 2011 (8.2 Thunderbolt) + apple VGAi adapter + Mountain Lion + external monitor---> didn't recognize

Macbook Pro late 2011 (8.2 Thunderbolt) + HDMI adapter + Mountain Lion + external monitor ---> didn't recognize

Macbook Pro late 2011 (8.2 Thunderbolt) + apple dvi adapter + Mountain Lion + external monitor + all forum sugestions ---> didn't recognize

Frustating

I was unable to detect my external display (Sony TV via DVI to HDMI cable) after upgrading to Mountain Lion which worked fine while running Lion. I ended up solving the problem by running "Repair Disk Permissions" on my OS X drive in Disc Utilities and then rebooting and running it again (caught more file permission issues the second time around). After running it a second time and rebooting again my TV was automatically detected like it was with Lion. I hope that helps someone having a similar issue!

The solution I have settled on that works for me right now for connecting my Macbook Pro to my Samsung SynchMaster SA350 is a combined solution that seems to rely on a few factors:

- Having installed GFX Card Status and having it set to 'discrete' at all times

- Having connected my Samsung Synchmaster SA350 to a PC and updated its firmware

- Switching between either of my two micro-adapters if my monitor fails to reconnect to an adapter at any one time. Using a HDMI cable to connect to the monitor I have two way to connect the cable to my macpro. My first adapter is a noname Micro Displayport to HDMI. My second adapter is a Dynex Mini to DVI daisy chained to a DVI to HDMI adapter.

Basically, for some reason, when I alternate between using either of my two adapters, my macbook pro and my synchmaster are able to find one another again. If my monitor fails to connect or reconnect, I have no way to predictably resolve the connection using the same adapter, leading to lots of time wasted, rebooting my mac, plugging/unplugging cords until the issue seems to magically resolve itself. But, if I simply alternate my micro adapter configuration, my Samsung instantly connects with zero added hassle.

My Hunch is that if I spent the extra bucks on an Apple micro to HDMI adapter that there would be no issues. But as things go, I'm happy that I have found a reliable solution to this widespread problem.

I also have this problem (2010 13" MBP with miniDisplay Port to LCD Cinema HD Display). It works fine with my Lion OS machines - but the Mountain Lion machines won't detect it. None of the discussed workarounds do a bit of good. Anyone find solution?

no idea

Did you run down this list:

1. Firmware update for your monitor using a pc

2. run gfxCardStatus and set it to discrete

3. your adapter is an apple Mini-Port to HDMI

?

Did it all, yes.

Sorry that I don't have any good further general advice. The only last word of advice that I have is to try what has worked for me and to alternate the adapters that you use; with my synchmaster, it seems to completely refresh a connection when it reads a new adapter configuration.

jjtomsic, did you address the issue of your display after downgrading to Lion? could you let me know? thanks.

***RELATIVELY FIXED***

I have an early 2012 macbook pro 17" and like most others who posted here, it was working normally with my samsung P2770 HD then suddenly stopped. This is the steps that I do and it works every time for me now. Unfortunately apple havent addressed this issue yet but I really hope that what I do works for everyone else. I have seen it posted once or twice before but maybe it has not been understandable.

1.go to disk utility (search it in spotlight if you cant find it) (make sure the hdmi adapter is UNPLUGGED from the mac)

2. when the window opens go to the left side of it and click on 'Mackintosh HD' or whichever hard drive you are using.

3. on the right look for the button that says verify disk permissions, it should be clickable, so click it.

4. once that is done, click on repair disk permissions, it may take five or ten minutes to run.

5. once its done, (you may want to run it again) close your laptop lid. switch of your samsung monitor and unplug the power cable from the back.

6. plug in the hdmi cable to the adapter and the mac (so now the mac and monitor should be connected)

7. open your mac lid, open up 'display preferences' and check to see if the monitor is detected. If it has been detected see 8, if not, I dont know how to help, try repeating the disk repar stuff after a restart.

8. switch on your samsung monitor, and go to the hdmi source screen, hopefully your mac will flash and connect and display on the samsung. I have my samsung set at 1080p.

Hope this works for you, I dont need to run the disk repair everytime, but most of the times 😟 . you can see in when it is repairing that it has doing something in the display preferences files. I dont know what but I hope apple can have a look in there.

Reply back with your results please and good luck.

Vic