No HDMI signal after update

It does seem that the 10.15.1 update may have fixed the issue. Like others, I did also need to do the whole power off and unplug routine, and one time it still came back from sleep with the resolution messed up, but after a subsequent restart it’s running normally through my direct HDMI connection, and returns from sleep normally.

I’ll report back if I notice anything odd but this is encouraging.

“No... There is NO fix as of yet from Apple.

I just got off the phone with the Apple Engineering team, and they are still working on a fix, but have nothing to show for it at the moment. 10.15.1 has nothing in it to fix this, and if people are seeing changes in behavior it is most likely down to re-boots, and not cold-boots.”

Obviously you haven’t read the last few pages, several if us, but not all, have had success installing the 10.15.1 upgrade. This is not just a reboot fix, but a shutdown, pull the power cord, power back up and it still works fix. Might there still be something wrong? Sure, but my system looks and acts the same now as it did with Mojave.

i agree that Apple has yet to fully identify the problem, and solve it in a way that fixes it for everyone, but something they did with 10.15.1 fixed it for some of us (or at least it appears to). Possibly something is similar about the monitors that now work, and different about those that don’t, I suspect there’s a third group that never stopped working.

Well it’s Wednesday... “senior level support” called Monday morning and we spent 2 hours on the phone with no resolution. My mini won’t connect to any display via hdmi or us USB-C or any combination of the 2. So they made an appointment for me at the “genius bar” for Monday night. They tried all the same stuff, plus several different monitors and also attempted to connect a display via thunderbolt. Nothing worked, so they ran multiple diagnostic programs (including some “super secret” program... whatever), the result... all hardware working. 2 hours later, NO DISPLAY, NOTHING MORE WE CAN DO. They said it’s definitely a software issue, and my case has been sent to engineering.

It wasn’t a pleasant experience, as the technician “genius” initially had a bit of an attitude and wanted to replace the motherboard and reinstall Mohave... would take a week, and my time machine backup wouldn’t be useable because it was created with Catalina.

I’ve ordered a USB-C to DisplayPort cable because they didn’t have one... my last hope to get my $3000 paper weight working again. At this point, I’m not sure how I would even get a “fixed” update on my computer since nobody can boot it up. I can’t even begin to convey the level of frustration, disappointment, and quite frankly disgust I feel toward Apple at the moment.

Their latest updates (including IOS) have been anything but trouble free. I don’t know what’s going on out there lately but it’s not good and some senior level people need to be called out. To have such a major OS released before it was ready just to make an artificial deadline is a very clear sign of a negative change in the culture and direction of the company.

Now that I've upgraded to Catalina 10.15.1, my problem has been partially fixed. If I restart the computer using the Restart command, HDMI is not recognized until I unplug the HDMI cable from the Mac Mini and then plug it back in. If I totally shut down and then power up using the power up button on the Mac mini, the HDMI is recognized from power up and both monitors work. Most of the time I can go into and out of Sleep mode with no problems, but once in awhile HDMI will not work when coming out of sleep mode.

Same problem here. When I start my MacMini (2018) my Samsung 4K monitor says: "not optimum mode" and doesn't work. It's connected via HDMI and that happens since I updated to Catalina.

When I type in my password "blind" and to start Mac Mini, the monitor wakes up and works as it should. The problem is the booting process.

Since there were some advices here, I bought an "USB-C --> HDMI" cable. Now there's a slight improvement - SOMETIMES the monitor keeps starting just normal when I boot the mac. But a lot of times it stays as black. At least the error message from Samsung is gone now.

Apple, please fix this. :-/

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.

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

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.

Apple has issued a technical bulletin advising Mac Mini users not to upgrade to Catalina..

PRAM & SMC reset worked for me!

Use USB-C to HDMI or DP. VGA? What year is this..

Glad I found this thread, I guess misery loves company. Same issue, Mac mini 2018 into Toshiba UHD TV (43LF621U19). Same symptoms, worked fine with Mojave, can restart fine, but if you power down nothing. I've been plugging in a Vizio HDTV, then switching to the Toshiba at the login prompt, a real pain. I'll try the scaling suggestion, but that doesn't give the resolution I bought a 4K Monitor for.

This doesn't help with the actual issue, but I have had success with another workaround albeit an expensive one.

I received and set up a Sonnet Breakaway Box eGPU along with an MSI Vega 56 card. It is working well with Catalina 15.0 so far. I've connected my three 4k Dell monitors using DisplayPort on the Vega 56 card -- have not tried its HDMI connection yet.

The UI is smoother with the Vega card and Windows apps under Parallels, especially Quicken Home and Business, that struggled to redraw the screen are noticeably faster.

Note that only the Vega cards are working smoothly. Though RX 570 and 580 cards are theoretically supported and worked with Mojave, they're also not playing well with Catalina.

I have a *similar* issue.

The issue that I have is display distortion.

Mac Mini 2018. Samsung UH750 monitor (4K). There are two HDMI ports on the back of the monitor. HDMI 1 is for 30 Hz, HDMI 2 is for 60 Hz. No problems when using HDMI to HDMI cable connected to HDMI2 with Mojave. However, the same configuration on Catalina causes the display to be severely distorted.

I've tried an NVRAM reset -- did not work.

I've tried plugging into HDMI 1 (30Hz) -- works but is suboptimal

The *ONLY* resolution I have found is to manually cycle through the input sources on my monitor. When I cycle back to HDMI 2, the distortion goes away.

Still... this is a very annoying issue to have to manually cycle every time the system boots up.

I expect more from Apple.

Update: I happen to catch on another forum that this workaround seems to kick the HDMI back on for 4k@60Hz. In my previous post I mentioned my setup as (2) 4k monitors running on usb c and (1) 4k monitor running on the HDMI port. The workaround that is now working for all 3 monitors is this: (1) monitor running directly into the HDMI slot, (1) monitor running directly into a usb c slot, and (1) monitor running into a usb c to HDMI adapter. After a SMC reset...all three monitors now working again on my mac mini running Catalina.