Yosemite does not recognize external displays...

It appears after research that in an effor to thwart the Thunderstrike Virus/Vulnerability Apple has closed down the Thunderbolt port to only cables they provide or support. Unsupported cable drivers are not listed within the 10.10.2 code therefore they will not allow for a display to work with any real frequency. (They may work temporarily after a PRAM Reset). This is what I have tried:

- Reboot

- SMC reset

- PRAM reset

- consistently three times the PRAM/SMC reset

- repair disk permissions

- repair disk

- Onyx Automation

Unfortunately, unless Apple allows the cable drivers I am using to connect to my 27" HP Monitor it will not work. The only options I have found that work are as follows:

1. Recover system back to 10.10.1 from a Time Machine Backup

2. Buy supported Apple Adapter. (unfortunately there isn't one for me)

Hope this helps.

After testing several hours with different machines (and I'm only using Apples cables), that the cables and monitors worked individually on both Thunderbolts ports, I was more or less giving up, when I got an idea, and it turned out to be a combination of several things:

- for whatever reason the energi savings was suddenly set to "Display sleep" at 1 minute (not by me) Since I'm using 2 high resolution displays with about 8 virtual screens, it apparently took longer to load than the limit in Display sleep" so the MAC never sent a signal to the displays

- I didn't realize that the update disabled bluetooth and therfore the mouse, keyboard, as I used the the Mac Book Pro's keyboard after opening the lid.

But I was seconds from going back to 10.10.1...

Hey. I just reinstalled OS X Yosemite 10.10.2 and I still cant get a signal to my HDTV.. It really *****. Havnt tried the PRAM/NVRAM since I have just installed with clean slate. So whats up Apple. Care to fix this. Seems this is causing some major trouble every kinds of people.

yeah im also thinking about reverting back to osx 10.10.1 but time machine is really not letting me do it S::S:S:S anyother way I can download 10.10.1

I don't think non-Apple cables are the main culprit. There is something else going on here... I am using a non-Apple cable (mini displayport to HDMI) and after several frustrating days of restarts and hair-tearing it now works fine, every time. I have no idea why it decided to start working. It did not seem to occur after something that I did.

I was on 10.10.1 at the time, now I'm on 10.10.2 and it's still fine.

Since it's working, this leaves me unable to test my other idea of installing Mavericks on a partition and seeing if that was any better. But perhaps someone else could try that.

When you are in restore your time machine should list different times and version when it was backed up. You just need to select the Time Machine Backup that have version 10.10.1 next to it. This will take some time. The other alternative is to install Yosemite from scratch and then using the migration tool recover your data from Time Machine.

Honestly, I am always able to revert to the previous version via my Time Machine backup.

Are you using the Non-Apple adapter that is sold on the Apple website from Belkin or Moshi ? If so I have heard those for some reason work and is supported.

For me I have tried all sorts of fixes but only able to get it to work intermittently while on 10.10.2 if I do a PRAM Reset and then unplug the cable and then plug it back in. As soon as it goes to sleep it will stop working again. That is why I stated it doesn't seem to work with any regular frequency. I am glad however you got yours working. My 27" HP ZR2740w seems to be down for the count on 10.10.2. Maybe it's because it a HP Displayport to Thunderbolt cable which is very aftermarket and not standard.

I am staying on 10.10.1 for my iMac until I can see a fix being successful. However my Macbook Pro is on 10.10.2 without issue because as I would theorize it doesn't have a thunderbolt port only a mini-Displayport.

Thanks - yes it is a relief to have it working. such a frustrating problem.

But no, my cable isn't Belkin or Moshi, it's IBRA.

Don't waste your money buying expensive adapters as this is definitely not the issue. I've received the Moshi 4K DisplayPort to HDMI adapter today 02/02/2014 which I ordered from Apple store (and which was suggested by another user in this forum). Tried with Macbook Pro (Mid 2012) on two different monitors and still have exactly the same problem blank display no signal. Hoping I can return this adapter as it cost $50AU.

Next I'm trying a complete format and fresh install of the latest version of Yosemite which I downloaded yesterday. I will post my results.

Feb 2015 - I've now tried the following without any luck.

1. Erased HDD and completed a fresh install of Yosemite 10.10.2 latest installer. No change. Cannot get external display to work using DisplayPort. Tried two LCD monitors and Panasonic 65" Television via HDMI. Have tested cables and displays with XPS ultrabook connected to DisplayPort and they work fine. Even tried Moshi DisplayPort to HDMI (4K) purchased from Apple store.

2. Tried SMC and PRAM resets after fresh install. No change

3. Erased HDD and completed a fresh install of Mavericks 10.9.4. Even on Mavericks I no longer cannot get DisplayPort to work anymore.

4. Also tried SMC and PRAM resets after Mavericks install. No change.

I'm conceding the DisplayPort on my MacBook Pro has been made inoperable by either a firmware or other update which came out around Yosemite 10.10.1. Unfortunately I waited to for 10.10.2 believing it may fix the issue and now my Applecare warranty has expired.

History of my issues - Macbook Pro (Mid 2012) had been working fine with external displays on Mavericks and even original release of Yosemite 10.10. Following 10.10.1 external monitors connected via the DisplayPort stopped working (blank display no signal) and I haven't been able to get working since even when reverting back to Mavericks.

Would be interested to know if anyone else has found the same results.

OK - I'm another affected user, my experience is that it works for some displays/TV's but not all. For example since going to Yosemite, it no longer works on our 37" LG LCD TV, but does on our 22" LG LCD TV. Works (sort of) on a Toshiba 32" TV but I now have to go in to mirror the display and set to 1080i - BUT having done this the picture is noisy (glitches on/off with some interference also).

In short it's not working as it used to. Both cables are aftermarket (non Apple sold) but they did work flawlessly previously).

Right now I have to concede that my Apple device cannot be connected to displays/tv's via HDMI - for presentations I now borrow my wife's Windows machine - how good is that?

HERE'S A FIX: turn off your MACs sleep mode.

It's not a great fix but it works on OSX 10.10.2

I'm in the same conditions. I just needed my MBP (late 2013) connected with a projector to teach to my first class and, of course, it didn't work. The MBP don't even recognize the screen. It's like I don't plug the adaptor at all....

I went to the apple store and they told me the thunderbolt is a dead port, so they have to replace it. My warranty expired last month, they asked me 300$...

But now I'm wondering if I should spend that money, since, for what I can see, it could be a Yosemite problem.

I tried everything I read in this post, but nothing...

Do you suggest to replace the ports? 300$ is a lot of money... 😢😢

Please suggest something!

Thanks

Apke

Rollback to 10.10.1 and if that doesn't work then I would have the port replaced?

Guess what? Time machine wasn't on, so I don't know how to get back to 10.10.1