External display not working after installing MacOs Catalina

Maybe this might point you in the right direction.

I fixed my full time pink screen issue, here is the solution. I think it might apply to your issue as well. For those of you without working screens, I suggest finding a screen that does work temporarily, and installing Teamviewer, or some other free program to remotely log into your machine. After doing so, connect the nonworking screen, start the computer, and log in remotely, then follow the steps 1-5 below. you will have to switch back to the working screen for the steps 6-15

The reason it is having an issue, is after the update, the signal being sent is YCbCr instead of RGB like your monitors are expecting. Some people with panels like mine will get pink, others likely get no signal recognized. This script works by setting up a profile for your specific monitor, and having it be forced to be RGB, if you connect it to another model monitor with the same issue, this process will need to be repeated for that monitor as well.

1. Download this script: https://gist.github.com/adaugherity/7435890
2. Place the patch-edid.rb file into the /Users/ directory
3. Run this command in Terminal: ruby /Users/patch-edid.rb
4. Take note of the DisplayProductID and DisplayVendorID file names. These will vary based on your monitor.
5. Move the output file named "DisplayProductID-XXXX" from /Users/~username/ to the /Users/ directory
6. Reboot your Mac in Recovery Mode by pressing Command+R as soon as you see the Apple logo after rebooting
7. Open Disk Utility in Recover Mode
8. Check to see if "Macintosh HD" is mounted. If it isn't you will need to mount it before proceeding.
9. Exit Disk Utility
10. Open Terminal in Recovery Mode
11. Change to the Overrides directory via "cd /Volumes/Macintosh\ HD/System/Library/Displays/Contents/Resources/Overrides/"
12. Create the folder with "mkdir DisplayVendorID-XXXX".
13. Run this command in Terminal (make sure to include spaces):
14. "cp /Volumes/Macintosh\ HD/Users/DisplayProductID-XXXX /Volumes/Macintosh\ HD/System/Library/Displays/Contents/Resources/Overrides/DisplayVendorID-XXXX/"
15. Restart computer and the monitor should now be in RGB mode.
16. Check to make sure it has taken effect by going to your "system preferences" and clicking "displays". If your display name at the top bar does not include "forced RGB mode (EDID override)", it did not take effect.

Hope this helps everyone! if you have issues look in the comments on the script page, the author is active.

My machine is a Mac mini (2018) i7 64GB 1TB. My monitor is a 28 inch Hannspree HF289H monitor

I had the same problem, along with Catalina. My fix:

Reset the SMC (System Management Controller), which requires a complete NO POWER state for 15 seconds...

iMac

shut down, then UNPLUG power chord for 15 seconds, then replug power chord..wait 5 seconds and turn on iMac

MacBook/Laptops

shut down, remove power chord, on internal keyboard-Left SHIFT,CTRL,OPTION,ALT, AND Power BUTTON down

ALL AT THE SAME TIME - 10 seconds - then repower

Older Macs

shut down, unplug, remove battery hold power button for 5 seconds at least, replace batt, repower, turn on.

This fixed my 2013 iMac...

Hope it helps..

Dsuggs wrote:

...

is it more obvious to me now that the Mac is cycling through different resolutions until it finds the one that matches the monitors but it is still struggling.

that is NOT how it works at all.

to get a Mac display to become active, you need the Mac to query the display, and the display to answer with its name and capabilities. Otherwise, the display will not be shown as present, and no data will be sent to the display.

This query is only sent at certain times:

• at startup

• at wake from sleep

• at insertion of the Mac-end of the display-cable, provided everything on that cable is ready-to-go

• on invoking Option-(Detect Display) button in Displays preferences

so try doing some of those things and see if the display comes alive.

Modern Displays with multiple ports are sometimes busy scanning the other ports, looking for an input, and miss the query from the Mac. They need to pay attention to the port you are actually using, or they will miss the query.

Some displays have On-Screen Display settings that can be used to tell the display a computer is attached on a certain port, or a certain port should be highest priority. Changing those may make your display more responsive.

Some displays include their own private "sleep" settings for the display alone. This can allow the display to enter its own sleep mode, on top of the Mac's not sending it data. A display that is sleeping on its own cannot respond to the Mac's query, and will stay dark.

I have similar problem on my 2018 Mini and this worked for me; under "Energy Saver" in settings make sure "Prevent computer from sleeping automatically when display is off" is CHECKED.

You also may need to reset the SMC

Here are the instructions for resetting SMC. They do not require a working monitor.

https://support.apple.com/en-us/HT201295

I understand that not having your monitor working is serious but we are users like you, trying to help so shouting is not welcome (writing in all caps is considered shouting).

open System Preferences->Displays, hold down option key and click Detect Displays.

Than remove cable and try the above steps again in this case you dont need to re-start your macpro again and again.

I had the same issue. After upgrade to Catalina, my other external display just went black but it is detected by the system. I'm using an HDMI-> USB converter . This one worked for me:

System Preferences -> Security and Privacy -> Privacy

On the left column, select Screen Recording

Select DisplayLinkuserAgent

I am pretty sure this is an issue with HDMI and Catalina. When using my two external monitors with USB-C to HDMI leads it takes ages for them to be recognised (30 mins or more). I switched them for USB-C to DVI cables and the monitors are recognised instantly.

If you have more than one monitor, you will have problem since macOS does not support Multi-Stream Transport (MST).

Explanation: https://us.targus.com/blogs/discover-targus/macbook-doesnt-support-multi-stream-transport

You need a dock specifically designed for Mac, or have one screen as a Thunderbolt screen.

Ironically, if you load Windows on to the Mac, it will work.

If you only need one external external monitor over DP/HDMI, you can make the dock work, but need to load the DisplayLink drivers from the DisplayLink website.

Apple shows no interest in supporting MST.

to get a Mac display to become active, you need the Mac to query the display, and the display to answer with its name and capabilities. Otherwise, the display will not be shown as present, and no data will be sent to the display.

This query is only sent at certain times:

• at startup

• at wake from sleep

• at insertion of the Mac-end of the display-cable, provided everything on that cable is ready-to-go

• on invoking Option-(Detect Display) button in Displays preferences

so try doing some of those things and see if the display comes alive.

Modern Displays with multiple ports are sometimes busy scanning the other ports, looking for an input, and miss the query from the Mac. They need to pay attention to the port you are actually using, or they will miss the query.

Some displays have On-Screen Display settings that can be used to tell the display a computer is attached on a certain port, or a certain port should be highest priority. Changing those may make your display more responsive.

Some displays include their own private "sleep" settings for the display alone. This can allow the display to enter its own sleep mode, on top of the Mac's not sending it data. A display that is sleeping on its own cannot respond to the Mac's query, and will stay dark.

Hi

I had a similar problem connecting my MacBook early 2016 12" Retina (running Catalina 10.15.4) to the LG 24md4kl external display...

I tried SCM and PRAM/NVRAM reset - nothing.

I tried different cables - nothing.

Having spoken to Apple Support I ultimately got connected with a very help guy based in Wales.

Through some trial and error - turns out it worked by connecting the USB-C from my laptop to the first Thunderbolt port on the monitor - very counter intuitive - but it worked - and the display is delicious :)

Hopefully this will help someone else.

In System Preferences->Displays.

The Detect Displays button only shows when you hold down the Option key:

This happed to me, too.

Unplug the external monitors and restart your Mac. Once it's up and running, plug in the first external monitor, wait for it to light up, then plug in the 2nd one.

Worked for me...

The same happened for me, except my Viewsonic display worked intermittently. I bought a new HDMI-USBc to connect screen to MacBook Pro. I made sure the cable had the correct refresh rate for the viewsonic display.

it works perfectly.

As a not too techy guy it is difficult to know when buying peripherals and we should be able to rely on the headlines: HDMI-USBc and not have to try to find other details such as refresh rate or frequency within the product spec as often the manufacturers don’t include it.

I had the same issue with my external monitors which were connected via HDMI.

They appeared black, despite the fact that they were visible in 'Arrangement' window, and I could see the mouse moving.

Fixed the issue by clicking on the 'Mirror Displays'.

All screens turned on, and then I turned mirroring back off to use as per usual.