MacOS Sierra not recognizing external displays and going black

Sometimes the cause is as silly as leaving caps-lock on when typing a password.

In this case, many monitors have multiple input ports, HDMI1, HDMI2, HDMI3, VGA1, VGA2 etc. If your monitor is not programmed to use the signal from the same port as the input cable, your screen will stay black.

Also, assuming you are not in the middle of a power-cut or anything like that, you should look to see if the monitor power cable is plugged in correctly.

Lastly, you should rule out a problem with your monitor by making sure it actually works with a different laptop.

I am pretty sure it's a Sierra bug, especially for hdmi adapter.

My latest MacBookPro USB-C to hdmi or legacy MacBookPro/Mac mini's Thunderbolt2 to hdmi are all having this issue.

As long as the MacOS went to sleep, and the to-hdmi adapter port off(e.g: monitor power off)/unplug, next time the port becomes on/plugged. Sierra detected the hdmi monitor but won't display anything(no signal/black).

Then you have to restart Sierra to make it work again.

Note: I tested at least 3 adapters and 1 OWC thunderbolt2 dock with 4 monitors/tv. They result same issues and we're working well before Sierra. It definitely is a Sierra bug, and not been resolved yet(10.13.3)

I too had this problem. I recently upgraded my Mac Powerbook to Sierra, and it wouldn't display on an external projector. (I discovered this just as I was starting a lecture for a graduate course I teach. Could have been a catastrophe. Luckily I had the next lecture ready, which was to be covered solely on the black board, and so did that instead.) It turns out that the problem was that I was using a 3rd party non-Apple vga adapter. Later I tried an official Apple "Mini DisplayPort to VGA Adapter", and that worked fine. After some web research, it appears that most 3rd party mac-to-vga adapters don't work with Sierra.

I recently upgraded to the 10.12.4 and now I can't connect with my Samsung tv monitor. There is audio but it only shows a partial desktop with the progress bar. It used to work fine till this upgrade. What do i do??

Hi, I solved this problem.

1. You need to disable System Integrity Protection

http://osxdaily.com/2015/10/05/disable-rootless-system-integrity-protection-mac- os-x/

2. Rename the kext

/System/Library/Extensions/AppleGraphicsControl.kext

to

/System/Library/AppleGraphicsControl.kext.bak

3. Copy old /System/Library/Extensions/AppleGraphicsControl.kext from Time Machine (or download)

4. Open terminal and write

sudo chown -R 0:0 /System/Library/Extensions/AppleGraphicsControl.kext

sudo kextcache -u /

sudo kextcache -i /

5. Reboot and enable System Integrity Protection

Hi All!

I work for a large school district in North Kansas City, Missouri, and we've experienced a very similar problem after we upgraded our teacher MacBook Air laptops (13 inch 2015) to Sierra. We had a large number of classrooms that we could not connect the projector to the laptop. As soon as we plugged them in, using a Thunderbolt adapter (mini displayport to VGA), the laptop display would go black and eventually it would cause a kernel panic and the laptop would reboot. This would happen over and over until you disconnected the video adapter. However, this never occurred before we upgraded to Sierra. The only solution seemed to be replacing our 50-foot cable bundles with ones that worked. These cables are expensive and not easy to replace as they run through raceway and above ceiling tiles.

At first, we suspected poorly-shielded cables or that maybe a video chipset driver (modified in Sierra) reduced the video signal output in order to conserve battery power. But, we eventually started wondering about the wiring (pin-out) of the cables themselves. We tested several different types of cables and we found one thing in common; all the cables that worked flawlessly did not have pin 11 connected to pass a signal through. The cables that would not work were using pin 11. I did some research on the web and found that pin 11 is often used as an address or ID for external monitors to send data back to the host machine. So, we decided to "convert" a few of our non-working cables by removing pin 11 to see if they would work normally afterward. Guess what? They did! So far, we have resolved several of these issues using this fix.

I don't know if this will solve anybody else's problem, but it might put you on the path to fixing your issues if you are using an external display connected through a VGA cable.

Good luck!

ditto your issue.

It worked before the update.

What is puzzling for me is that I can use a Samsung Display, but cannot use my VIZIO 23" tv. Before the upgrade I was able to use both via the two ports on my MacBookPro.

Yes indeed, any help is invited with much welcome.

Thanks.

joe

I got 2 MBA both running with Sierra.

One can detect the external monitor, the other can't, using same cables and same Mini Display Port cable.

I have rebooted a few times, and reset the PRAM. Nothing.
In both cases, the external monitor detects I have connected a HDMI device.
The problem only appeared after having upgraded to Sierra.

The macbook connecting to my external monitor is a MBA Sierra 10.12 with graphic Intel HD Graphics 6000 1536 MB.
The macbook not detecting the external monitor is a MBA Sierra 10.12.5 with graphic Intel HD Graphics 5000 1536 MB.

I have reinstalled El Capitan on this mid-2013 MBA and still no luck. Seems like the Mini Display port has packed up for good. Can't wait to get a laptop with only one USB-C failing on me in just over 3 years time.

Hello,

Exactly the same for me with a mid 2012 15" macbook pro (non retina)

Going to back to El Capitan didn't fixed the problem ...

i've tried several adapters, official, non official, several cables = no luck...

BUT......the worst thing in this story.....I was visiting a friend , and i've tried to connect my macbook pro to his Apple Thunderbolt Display....and guess what....IT WORKS......

i'm really angry.....

I'm a professional musician and i absolutely NEED to have my macbook pro connected to my external 24" HDMI display......This macbook pro is still a beast with a quadcore core 7 and fully upgraded to a samsung SSD.......

Is it something Apple can fix ????
i've even tried to install WIN10 via bootcamp, just to see..... and it doesn't work too....

WHY DOES IT WORK WITH AN OFFICIAL APPLE DISPLAY ????

Please Apple , do something about it or it'll be my last MAC...

This is too long a thread to be able to clearly follow. There seem to be different problems in it, where some people may have had hardeare failures, others adapter problems and orhers software issues.

I suggest you start a different thread a post all the relevant information about your mac, OS and display.

FWIW I connect external displays to my mac in Sierra every day, including direct HDMI monitor, HDMI via miniDP adapter, vga projector, HDMI tv and an old imac in target display mode via Thunderbolt.

They all just work.

Just so no one else wastes their time on this like I did, I'll post me experience here.

With my MBA 11" I was using a 3rd party display and MDP to HDMI adaptor for 2 years on Yosemite just fine.

Upgraded to Sierra to resolve a photos bug, and found my display no longer worked. Rolling back to Yosemite did not fix it, and given the official explanations here, that implies a hardware fault. However now using an apple certified cable has fixed it.

The only conclusion is that a Sierra update installs firmware relating to the Thunderbolt port and external displays, although no-one at Apple support would dare confirm it, let alone dream of suggesting it. Luckily I finally spoke to a senior tech who admitted that that was a possibility, and suggested I just try an Apple branded adaptor.

Honestly I'm fine with Apple forcing us into hardware upgrades, that is their business model and it's our problem if we choose to buy into their ecosystem. However what I really can't stand is the shadiness and evasiveness that ends up wasting a huge amount of my time. Just admit that Sierra installs a firmware upgrade and we can all get on with it! Anyway, the good news is that for some of you the fix is 'only' €40.

We had a few iMacs with a related issue when updating to Sierra. This is using Apple adapters to VGA projectors.

-External display off, computer off, adapter plugged in = hangs on startup

-External display off, computer on, plugging in adapter = computer black screen

-External display on, computer off, adapter plugged in = works normally

-External display on, computer off, plugging in adapter = works normally

I have a sort of issue, my external monitor work fine ( it's just a philips tv ) but if i boot my macbook pro (13 mid 2012) with it connected I can't turn on the macbook integrated display anymore, opening the display it's black every time. If I boot the macbook without the external monitor and connect it to it later i can switch between the two with any problem opening and closing the screen. Any solution?