Yosemite does not recognize external displays...

I had a similiar problem with my Mac Mini and 10.10.4. The monitor gives the notice "Input not suppurted ". More i had strange problems with hanging up systems in iMacs during switch off procedure. In my case the problems were solved after unchecking the box "do not disturb during monitor sleeping " in the messages control center.

After an endless search to get my once upon a time perfectly fine working but not working now Monitor after Yosemite (thanks for bizarre updates and regulations apple! ) I HAVE FOUND THE SOLUTION.

My 21" philips ips monitor is now working with Late 2008 13" macbook like before,

Problem is gone by turning off kext from terminal.

If you google how to turn kext off, you will find it.

And please read some articles before doing this.

Guys,

I had the same problem.

The problem is the cable. I changed the cable, buying original one, and it works fine.

Just try

I called Apple today about this issue. Here's the bottom line: Apparently, it's a resolution incompatibility issue. Probably caused by one of the OS X updates.

I had a late 2008 MacBook Pro (MiniDisplayPort) worked with my (?2008?) 32" LG TV - until around the time ~I upgraded to Yosemite.

I got a 2011 17" MBP & Thunderbolt never worked w/ LGTV. Took both MBPs to Apple store w/ my (non-Apple) HDMI cord & HDMI to MDP adapter & the guy at the Genius Bar got EVERYTHING to work on their non-Apple monitor. When I got home, neither worked. Before I recently sold the 2008 MBP, I switched out the 1TB hard drive for the 500GB that was in it before.

The 500GB had Mavericks on it - and I tested it with the LG TV - it worked.

Yesterday,I got a late 2012 15" MBP retina w/ Yosemite & nothing worked (2 Thunderbolts, HDMI). I figured it was a Yosemite problem.

I called Apple & we worked w/ the retina model. After a couple hours of trying, (t) ried a number of resets, add a new user, etc..Apple tech, Bjorn, asked me to try another external display, so I took everything into the living room & hooked HDMI to HDMI into the 60" Samsung & opened Preferences --> Display, & it opened a 2nd SAMSUNG window that worked right away.

BUT neither of the ~Thunderbolt ports worked - which ~MAY have been a problem w/ my HDMI - MDP adapter, so I didn't pursue that.

Bjorn said it was due to incompatible resolutions.

Since there apparently isn't a way to check the exact resolution in Display Preferences or on either of my TVs, I don't know which resolutions work & don't work.

If anyone has the ability to check which TV resolutions work, let me know. Looks like I'll be buying a new TV.

Do you know what the various resolutions are of your TVs? If so, can you please post which ones work / don't work?

I called Apple today & they said it was a resolution incompatibility issue.

I'd used my 32" LG TV for years as an external display on my old 2008 MacBook Pro until around the time I upgraded from Mavericks to Yosemite.

I upgraded my MBP models twice in less than a year to resolve the problem. Last week, I bought a model A1398 retina because it has 3 ports that support displays (2 Thunderbolts & 1 HDMI) After I couldn't get ANY of them to connect, I called Apple (today).

After troubleshooting for an hour or 2, the Apple tech asked if I had another display & I tested the A1398 model on the 60" Samsung in the living room. The HDMI connection worked. The Thunderbolts didn't. I didn't have an other few hours to sort that out, so I'm happy to know that something works.

After I hung up, I wondered why a resolution issue would affect the HDMI port, but not the Thunderbolt ports.

Now I'm wondering if I really do need a new TV, or if there's something else (obviously, a lot of people in this forum got a lot of other things to work).

You were the only one I saw with LG TVs & other brands to test, so maybe you'd have some idea whether resolution could be the problem or not.

On your TVs that did work, did each one open a 2nd window in Display Preferences? (that added a "appearance " option to Display/Color options bar)? If so, did either window recognize your display by brand name?

Since there isn't a drop down menu with compatible brands/models, I'm curious to know if Yosemite automatically recognizes all compatible external displays by brand name (or model, or resolution, or some other clue about what's compatible?)

I can't find any display resolution controls on my TVs, & Display Preferences in Yosemite doesn't show that option either, so none of that helps me determine ... anything.

I'd think that if resolution really is a compatibility issue, that there would be an easier way to figure out which non-Apple external displays will work. But then, maybe that's their intention - to get us to buy only Apple products.

just turn off the Kext and it will go away,

It works %100,

kext is obstructing non-apple cable, adapter, monitor, tv etc. as they are 3rd party and osx is not trusting them.

Thats why they dont work.

Unplugging the monitor worked for me, too! I'd tried all the resets, restarts, monitor off/on, etc. But a simple unplug and plug back in worked immediately.

At least for now, updating to the latest Yosemite Public Beta 10.10.5 has fixed the issue for me. Only been through 2 restarts though so fingers crossed the good luck holds!

No longer working. The behavior has changed, though. Now the system recognizes the monitor as connected, changes resolution, says its mirroring, etc - but can't get anything to display on it.

Suppose this is an improvement since before it didn't even know one was connected.

The suggestion to turn off kext has not worked for me (neither has anything else: resetting nvram, turning monitor off and on, unplugging monitor, etc.) I'm using MacBook Pro, 10.10.4 and a Samsung monitor with mini-display/thunderbolt -> Digital/DVI Apple adaptor.

Turning off kext signature worked for me for about a month.

Now It has the same behaviour again. COME ON APPLE FIX THIS MESS!

I finally got it working. Based on a vaguely related discussion https://discussions.apple.com/thread/6623697 I tried the following steps

Apparently, I needed to reset the SMC before resetting the PRAM/NVRAM. Here are the steps that I did, who knows how many matter

(1) Disconnect External Monitor.

(2) Restart in Safe Mode

(3) In Safe Mode, repair permissions.

(4) Shut Down, reset SMC

(5) Once computer boots from SMC reset, restart again and reset

PRAM/NVRAM.

So far (5 days) it's worked pretty well.

For what its worth I took my laptop in to the Apple Store, they diagnosed it as a problem with the logic board, and replaced it under warranty. Just got the machine back and it works 100%. So some of you may be having hardware problems.

If you are using external monitor for several years and it begins not working after an update, problem is definately the update! not hardware issue.

And it happens to god knows how many people all around the world!

It is clear that there is some kind of bug and needs to be fixed right away.

PS: I turn on kext from terminal, shut down, start again, and turn off kext from terminal, shut down, start again and my Philips external monitor works again!

Restarted several times and still works.

Anyways, I shouldnt be writing codes to terminal to get the external monitor work!

Hi, just a datapoint that may help others -

My macbook stopped working with Dell P2312H displays (DVI) after upgrading from 10.6.8 to yosemite (tried a bunch of monitors at the library). The result was static and lines.

I tried a bunch of things like resetting the PRAM, different order of plugging in, etc.. didn't fix it.

What fixed it was switching from a Monoprice DVI adapter to an official apple DVI adapter. The monoprice adapter still works on some monitors, just not this particular dell model and osx version for some reason.