my macbook pro does not detect external display anymore

I see this thread was started a while ago and there a few different problems...

I'm looking for some help as well.

My issue is I have a Mac Book Pro (2011), Apple Thunderbolt to HDMI adaptor and a Samsung 42" LCD TV.

For the last year or so I have had zero issues connecting to my TV (and others in hotels) via thunderbolt display port via my HDMI. My computer reconizes the display, It has worked flawlessly and also the audio worked through my TV. The Samsung always appeard in my Audio Setup as an output source.

I updated my mac about a week or so ago. I noticed the updates were for the thunderbolt port.

I plugged in my mac to my TV again and the video/screen appears and works fine.

But my audio is NOT working, and the Samsung TV does not show in my Audio Setup as an output source...

Does anyone have any ideas, suggestions...?

I have tried multiple TV's, cables and the normal power cycle stuff.. The display works but NO Audio.
And this worked before, As I do Audio and Video Editing on my 42" TV.

PLEASE HELP!

That is odd but it worked! Thanks! I had tried several other things before seeing that tip. 🙂

OMG..

how can I thank you enough!

cheers man

g.

Add me to the ranks of people who blew an afternoon trying to get an external monitor hooked up to a macbook pro. (In my case, an ASUS VH238H, with inputs for DVI, HDMI, and VGA.)

My MacBookPro10,1 didn't recognize the monitor until I followed this recipe:

- reset PROM

- use gfxCardStatus to force the discrete graphics chip

- disconnect HDMI plug from MBP, power cycle monitor, plug in HDMI

Neither DVI nor VGA worked, but the monitor's inputs and the cables are known to be good. So it's either the Thunderbolt outputs, or the Apple adaptors. From the comments here, it seems like a Thunderbolt driver problem, so my enthusiasm for debugging it is in the low "never gonna happen" range.

Many thanks to emgsilva and scottmil for the gfxCardStatus and PROM-reset clues.

Good luck out there,

Scott

Solution for me:

Symptom:

Ok, I have this problem and my MBP is 10.8. No matter direct HDMI or mini DP to HDMI, the computer can recognize the external TV but and the TV can detect that HDMI port but no signal can be displayed.

Solution:

while the hdmi is connected, turn off the TV, wait for a few seconds and turn it on again. Then it works, at least for now.

Hi all,

None of these issues worked for me, so I phoned up apple support which I got do via the support tab on the app store for mountain lion. I spoke to one technician who talked about drivers and suchlike and I asked to be escalated up. I spoke to a guy who took a snapshot of my computer info and said he'd get back to me in a few days.

I was puzzled by the fact that apple seem to be totally unaware of this issue despite all the comments on threads like these. So my advice is to go phone them up and make some noise!

Stu

I am having on going issues getting my 13" macbook pro to work properly with an external monitor. Tried with a Samsung, tried with a Dell. Both worked for a few days, then stopped working. I updated the firmware, still nothing. The Dell monitor error message says that "there is no signal coming from your computer" and it does not show up in airplay mirroring. I'm at my wits end. hard to work like this.

Unplug your HDMI cable from MBP and turn it off few seconds. Turn it back on and log back into your computer. Once you're logged in and all your startup programs loaded (if any) , plug in your HDMI cable back to your MBP and see if that works.

yeah - is anyone else thinking it just makes sense just to buy a pc and turf the mac? sort this problem once and for all.....

I suddenly had this same problem, and I think it was caused by constantly switching between monitors.

The computer was set on an external monitor resolution that one monitor could recognize and the other couldn't.

Changing the resolution preferences fixed it.

The same issue, I checked all the advice, it does not work. My setup,

MBP Late 2008, (NV 9400/9600 - 9600 is active), second display is Dell P2412H, I tried by Mini Display-DVI conncetor by Apple (BTW is going to very hot !), OS X 10.8.2.

OS detects the monitor but the monitor displays a message that it is not the signal and going to sleep.

Any idea ???? It is a curiosity that apple nothing with this problem does.

regards,

bw

Hi BWalecki,

Did you try changing the resolution on both the MBP and external monitor from display preferences? I think the monitor is not seeing the signal.

Hi Mitsuoko,

I left the second display setting preferences such as he discovered, but if the signal parameters are out of range of the monitor is not so, it (Dell hardware) displays a message?

but I check it.

No, change the resolution does't change anything the monitor to fall asleep because he claims - that there is no signal 😟

I've been following this long thread for what seems like forever!

I had the same kind of problem after I had been using my system for some time without difficulty. Unexpectedly, it stopped sending signals to the external monitor. I read the thread through, but duidn't get any help. It was irritating to say the least. My problem was solved when I figured out that if the Graphics option in Energy Saver preferences was set to Battery Saving the signal was too weak for the external monitor to detect it. As soon as I changed it to Higher Performance the image popped on and has stayed on for months without a problem. Now I just have to remember to set it back after I have taken the laptop out for travel and put it back on battery saving. Of course, I don't know how the setting had changed but who knows? I had posted this "fix" long ago and it doesn't work for everybody, but I thought it best to repost it becasue the thread is so doggone long and most of the attention seems to be on fiddling with cables and connectors.

FYI, I have a 15 inch MacBook Pro from late 2008 with NVIDIA GeForce 9600M GT 512 MB graphics card and running OS X 10.8.3. The monitor is an Eizo CG223W.

Of course, every setup is different with all the possible devices plugged in to various ports and God knows what other variables that could affect things.

Ed Merrin