No HDMI signal after update

Just got an HDMI to Thunderbolt 3 / USB-C adapter and I can confirm that this workaround works. I didn’t event need to restart. Apple owes me $16.

I made sure to get one that supports 4K@60hz. I can confirm that my LG monitor works with the Super Resolution + set to high, and the HDMI Ultra HD Deep Color (which I think is the problematic setting) on.

If anyone’s interested this is what I ordered:

USB C to HDMI Adapter (4K@60Hz), Warrky Certified [24K Gold-Plated, High Speed] Braided Type C to HDMI Adapter Thunderbolt 3 Compatible with MacBook Pro, Galaxy S10/S9/S8, XPS 15/13 and More -Gray https://www.amazon.com/dp/B07HVQQPYK/ref=cm_sw_r_cp_api_i_kJ3PDbEZST3TQ

I have the same or similar issue with my 2018 Mac Mini. I have both an LG 4k monitor and a Vizio 4k TV, each with a different HDMI cable. (Both cables are rated for 4k 60Hz.) After upgrading to Catalina the HDMI signal no longer starts when booting up. Each morning I have to 1) unplug the HDMI cable, and 2) reset the SMC, before the Mac Mini will booth with any signal sent to the display. This is the case regardless of which monitor or cable I am using.

I think I've found a temporary solution (until they hopefully will patch this) without having to reconnect my Mac Mini to a low res TV. My LG 4K display has a HDMI ULTRA HD Color feature. When I switch it off the display sees my Mac Mini. Anyone try this?

Further to my post above. Support completely unable to help. Then I decided to try plugging in a Thunderbolt to HDMI adaptor. Connected HDMI to HDMI lead from adaptor to monitor. By magic it worked and I am back up. But if anything this makes me even more cross. Why on earth didn't Apple Support suggest that simple and cheap fix, instead of telling me to take the Mini to the Apple store to be "checked out". Because they are either in denial, or really incompetent. It's clear that Apple didn't develop HDMI to support the Mini at the Catalina upgrade. Careless and reputationally damaging. Especially after recent Safari/E mail outrages.

This thread helped me get my LG monitor running temporarily at least. I turned of all the UHD settings using my monitors on screen menu and then force restarted my Mac mini. It started working again when I booted back up. Here’s what I disabled on my LG monitor:

Super Resolution +

HDMI Ultra HD Deep Color

I tried Ctrl+Command+alt+Shift+R before startup apple logo, it worked (TCL 4k), but only at the second or third try.

First it recognize the screen 2160@30hz, then it switched to 60hz at login screen.

A temporary fix. After trying everything I could think of with monitor settings/cables/changing settings through remote display... I found some help on another forum from someone who called support.

To summarize the issue: Mac mini - HDMI to HDM connection to a 4K display (many users with lower-res displays chiming in do not appear to have the HDMI issue). -- Another fix is to buy a USB-C to HDMI or Displayport adapter (if your monitor supports).

Temporary (I hope) Fix: Appears to be a SMC issue. Shut down the mini. Unplug for 5 seconds. Plug back in and hit power. This seems to fix the HDMI signal for a period. But it doesn't hold after display sleeps for a longer period. Hope this helps. Apple really released a buggy OS this go-around. Disappointing and I hope they get this fixed.

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

Yesterday I switched back to Mojave on my Mac mini 2018 successfully with not HDMI issues any more !!!

First try was to go back in "Time Machine" but without success. Mojave running but still same HDMI issues.

Second try, I decided to a make a fresh Mojave installation using internet recovery ... this stoped of after downloading installation files with an error.

Last try, I created a Mojave USB installation stick. At the end of the complete installation procedure all HDMI issues are solved and my system is running as before Catalina.

Hope this will give you a temporarily solution until Apple solved this issue finally.

Well... it's been awhile. I haven't had my 2018 Mini in my possession for the past 2 weeks.

I think the issue is now finally resolved.

They took my mini at the apple store after being sent there by "senior level support". The claimed it was a software issue because all the hardware checked out fine. They kept it for a week and then called saying it was fixed. I went to pick it up and was told it "was hung in the update cycle", they were able to "force the update and now everything is fine". Relieved, I told them they needed to start it for me. IT WOULD NOT DISPLAY... SAME ISSUE. They took it in the back, claimed to have fixed it again, but again when I instated the start it in front of me, IT WOULD NOT DISPLAY... SAME ISSUE. They took it back again, and it wouldn't even turn on. They decided it was a hardware issue and would order a new logic board.

A week later, I'm emailed that it's finished. Again I insisted the start it. It started as a new blank computer. They did not attempt to transfer my data as promised. No surprise based on the level of service I've received to date. Took it home, set it up and attempted to "migrate" from the last time machine back-up. Couldn't be found. WHAT??? I know it's there. So I decide to check the OS. It's Mojave, despite being assured this would have the latest board (flown from China, that's why it was going to take so long) with the latest OS... that was apparently more BS. I contacted "Senior level support", mostly a nightmare again for 2 hours. Finally I got someone who actually KNEW SOMETHING! We upgraded to Catalina. I restored from my back-up and so far all is well.

Apparently NOT ALL upgrades to 10.15.1 are created equally. For those running 10.15.1 and still having issues, but you have a functioning display (however you may have accomplished that)... go to the "apple menu" and select "about this MAC". Select "system report". In the listing tat comes up under "hardware" go do to "Graphics/Displays", select that. The last item in the listing that comes up under "Displays" (which should be your connected display) you will see "Adapter Firmware Version:" it SHOULD BE "2.15"

Apparently some 10.15.1 installs were NOT installing this for whatever reason. If it is anything other than 2.15, that is BELIEVED to be the issue... (or at least one of the issues). Hope this helps someone go in the right direction. MOST of the Apple people I dealt with were not at all helpful. Thank goodness for the guy I got last night. I hope my 2 MONTH Nightmare is finally over.

Same as everyone else, Mac Mini 2018. Was fine until Catalina update. I have tried numerous HDMI -> HDMI cables, Thunderbolt-3 -> HDMI and Thunderbolt-3 -> DVI and it's always the same. You hit the power button, and nothing but a black screen. The monitor will act like it's trying to sync with the Mac Mini, and then eventually goes to sleep. The behavior is the same with several different monitors.

Temporary work around: After booting to the black screen, triple-tap the power button. The Mac Mini will tell you which field it's in (username or password). Blindly type in and hit return. After it logs in, the screen comes to life and works perfectly.

If I shutdown and immediately reboot - the screen will work. But if I shutdown and let it sit for a while (say a couple of hours), then it's black screen, triple-tap the power button all over again.

EDIT: Forgot to mention: Tried unplugging/waiting/plugging in as others have suggested as well as resetting PRAM to no avail.

Samsung Monitor will not be recognized at system start on Mac Mini 2018 after Upgrade to OS Catalina 10.15.2.

No problems with OS 10.14 before.

My personal (hopefully temporary) bypass:

After having pressed the power on button on the Mac mini, I unplug the HDMI cable and plug it in again at the Mac mini. Afterwards, I switch the Monitor power on and everything is working fine.

It seems, that the Mac mini doesn't receive an interrupt from the monitor, if the monitor is already powered on at systemstart.

So for me, I have a samsung 4K over HDMI. Starting up, plugged into the HDMI port in the Mini, I get “not optimum resolution” warning with a black screen. If I switch the cable to my Anker usb-c hub with HDMI, then restart, it works fine. What’s really weird is, if I start plugged into the hub, then with everything on, switch the cable out of the hub and back into the HDMI port in the Mini, the display works fine. So HDMI port in the Mini IS sending a signal through HDMI, just not at start up? But the HDMI port in the hub works as it should.

I did all the usual stuff, reset PRAM ETC. Reinstalled Catalina, swapped cables, reset display settings to both scaled and default for monitor. None of these things worked. The only thing that works right now, as it should, is through the hub.