No HDMI signal after update

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.

I would call Apple Support, when they answer ask immediately for a "senior advisor". Then tell them that you updated to 10.15.1 and the issue you are having. Tell them that you are aware that the Adapter FW is NOT 2.15 which it should be, and how do they propose to rectify the issue. Unfortunately it has become abundantly clear that you need to take control with these people. Most of them seem to act like the "know all", but if you actually do know what you're talking about, it doesn't seem that you need much more than a basic knowledge to be on par or beyond their level of knowledge, they will quickly admit that you are more knowledgeable about the issue than they are, and usually offer to pass you on to a supervisor or research the issue and get back to you. Whether they actually will get back to you is questionable as well... It has become frustratingly clear that they have a script and check list they work off and no practical knowledge or experience ant the basic support level. It's questionable how much "knowledge and practical experience" the average "senior support" people have.

Mine is 2.15 and I still have the issue. I can consistently get it to work with lower res monitors, but 4K or 60hz signals are very iffy. Sometimes I can get it to work especially after at SMC reset. However, mostly I get "No Signal" unless I use a lower res 30hz monitor. I know a lot of people reference different HDMI or DP to USB C and I have tried many, but none of them consistently work for me. I've been in Microcenter and the Apple store and they always have the Mac Mini's connected to the very expensive LG USB C monitors. So I am thinking if I had a true USB monitor that would solve my problem, but USB C monitors are way too expensive still. I just need Apple to fix the problem. I had no issues on Mojave, so I know it is a software issue.

I experienced EXACTLY what you described, but mine continued to get progressively worse until no display would come on.

I bought and tried all the cable combinations suggested and nothing helped. Perhaps it is a hardware issue caused by Catalina.

They eventually replaced my logic board (essentially the whole computer). Mine has been shut down and restarted and is connected to my 4K 60 hz 32" LG display via HDMI. It seems to be working normally now. The logic board they installed had Mohave installed as the operating system, I upgraded normally as anyone else would, except I went directly from Mohave to Catalina 10.15.1, everything worked normally after the update. I then restored from a time machine back-up overnight. It's been working fine ever since. I suggested the 2.15 firmware because that was what the senior tech immediately asked to check. He stated that some people were on 2.14 after the update and in his experience (finally someone who admitted to having dealt with the issue before) those were the ones having issues.

Just trying to share my experience in hopes that it will help someone else get to a resolution. I know just how frustrating this is.

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.

Realizing that my warranty was soon to expire, I made another trip to the Genius Bar and demanded a repair. They replaced my logic board which is pretty much everything except the RAM, fan and chassis. New SSD HD too. So I got a nearly "new" computer, and it's pre-loaded with Mojave. No way am I gonna update to Catalina until Apple fixes their bug. My HDMI port works, just like it did before October, and I'm no longer using the USB-C to HDMI adapter chuck I was forced to buy.

This issue is clearly only affecting a "select" group of Mac Mini owners, so I suggest all of you who still have warranty coverage go demand a new logic board. Whether that truly solves the problem or not I don't know - I am back on Mojave now after all. What I do know is that if there are hundreds of ~$500 (internal accounting cost) warranty charges coming out of this debacle, Apple will put some priority on fixing this absurd issue.

the squeaky wheel gets the grease

I had the issue where after upgrading my external display would just show a blank screen. The instructions at site below fixed my problem:

https://appletoolbox.com/external-display-shows-black-screen-macos-catalina-and-other-issues-fix/

Basically I had to enable my display driver.

Hello everybody,

Today I noticed that 10.15.2 was released and I decided to give it a try.

I fully cleaned my Mac mini 2018 and installed Catalina from the internet completely new.

Finally I saw no more issues on my 4k Samsung anymore!

No issues during the installation and no issues after the installation.

Comparing the adapter firmware I recognized that it was now upgraded to version 2.16 with 10.15.2.

I hope that everyone will now be able to solve the nasty HDMI issues for Catalina and Mac mini.

I keep my fingers crossed.

I upgraded to 10.15.2 last night hoping my HDMI issues would be resolved. Sadly, not the case for me. However, in checking my firmware version, I'm still on 2.14. Does anyone know, that has talked to Apple Support, if there is a way to update this firmware manually?

OMG I think they partly fixed the issue. I upgraded to 10.15.2 last night with no luck. I still had to use the three power button trick to enter user name and password. Shortly after that the screen comes on. I seen the post today about the display firmware and I didn't check mine. I checked and there was no firmware number. I did notice that it was recognizing my monitor as a 5K monitor when it is only a 4K monitor. I had switched to a display port adapter video cable, because I couldn't get HDMI to work at all. I switch the cable back to straight HDMI to HDMI and it appears to work now. The display version is now showing and has been updated to 2.16. I've rebooted a couple of times and it brings me to the login screen that I can actually see. This is more progress than I have seen since the initial upgrade to Catalina. Here is to hoping that the issues are gone now! :)

I've upgraded to 10.15.2 and firmware now on 2.16 but if I boot up with my second monitor connected via usb c it still doesn't recognise my monitor connected to HDMI. I have to unplug the usb c connected monitor to force it to see the HDMI monitor and then plug in the usb c once its booted up. Everything then works fine. So not a solution for me unfortunately.

Fingers crossed they will eventually fix it.

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.

The problem was fixed for me with the newest update 10.15.3.

HDMI to HDMI now works just fine with my Samsung 4K monitor.

With USB-C to HDMI there are still some problems with a black screen while booting.

Anyway: I'm glad that it works now. I paid around $3,000 for my Mac Mini and had 5 months were I couldn't use it correctly. I am very disappointed that something like this could happen with an Apple product.

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.

This thread prompted me to try a pair of USB-C to DVI cables instead of USB-C to HDMI and they worked fine. Of course that doesn't help if your external monitors don't support DVI. Whatever the case it is still surely a software bug.