No HDMI signal after update

My Samsung Monitor will not receive HDMI from my 2018 Mac Mini after Catalinia upgrade. No amount of safe mode or resetting PRAM will help. Apple support are in disgraceful face saving mode, suggesting that I try with another monitor. I don't have another monitor. My set up was working perfectly until I made the fatal mistake of upgrading O.S. They want me to get the Mini "checked out" in case it is not working. It is working. It is the O.S upgrade that has killed it. Now no signal from computer to keyboard either. Whole system is dead. Thank you Apple. I will be getting my money back.

OK, so I too, have an LG UD2758-B and I tried your "temp solution"

which really is ALOT better than switching the hdmi cable to a low res monitor

to boot the mini and then switching back to the LG monitor

Now the funny part is, out of curiosity I enabled the option again and

shutdown/re opened the mini and picture is shown again.

BUT it's a pink color instead of black, and whole frame is shifted to the right ...

...until after I choose a user (i have 2 accounts on the mini) and then picture auto corrects it self.

Stranger and stranger things...

But thank u for discovering this, it beats having all the fuss of hdmi cable back and forth.

I sent in my Catalina-update Mac Mini 2018 to an authorized service center. The technical person tested the machine with an Apple monitor using all possible combinations (HDMI>HDMI, USBC>HDMI) and failed to get the signal detected by even the Apple machine. They did not know what caused the glitch. My Mini will be sent to a regional center for further checks. Its gonna be a stressful 2 weeks of waiting!

I have 2018 mini. Two monitors. One hdmi the other usb c. Worked fine first two days. Now hdmi has no signal. Good thing I had two monitors or I would have thought my mini was dead. Getting a usb c to hdmi. Monitor is HP 25es.

Given the issue is not resolved by rolling back to Mojave suggest it is firmware and not software.

given Apple have released a statement advising Mac mini users not to upgrade to Catalina they know what the issue is

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

It seems there are a number of temporary fixes for this problem. For me as long as I don't plug my 2nd monitor in on start up (USB C to vga) the HDMI is working fine. If I have my second monitor connected at start up I can't get anything on the HDMI at all . However I can plug the 2nd monitor in once it's booted up OK on the HDMI.

Still very frustrating as everything worked fine before the upgrade to Catalina. Hopefully Apple will have a fix for us soon.

A07570 wrote:

I’ve had a problem before Catalina with Mojave ‘waking up’ my monitor after the Mac was in sleep mode, often having to hit keys or click the mouse several times, I never had this problem with other minis or with HD monitors. Has anyone else noticed this with their 2018 mini and 4K TV/Monitor? Could this be something we have in common?

Occasionally under Mojave, my HDMI monitor was slower to wake up than DisplayPort. Once in a while, I had to power off the monitor then power it back on. So, HDMI wasn't perfect for me under Mojave either, but it wasn't enough of a problem to be worth chasing. I chalked this up to typical HDMI flakiness that, like you, I've seen from DirecTV and some other devices.

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.

Dammit! I thought it was all sorted out with a USB-C -> HDMI adapter, and it sort of is... except...

Did you know that the USB-C ports on the Mac Mini does not carry multi-channel sound? Well they do not. Hence, when you connect your TV to the Mac Mini via a USB-C -> HDMI adapter, you only get 2ch sound. So, if you are using Kodi for instance to play your multimedia files, the MP3 files work fine, but your Dolby Digital files do not.

The only multichannel sound interface is the HDMI connection, and it doesn’t work. Dammit!

The takeaway is that Apple upgrades cannot be trusted to be reliably developed. It's a short step from there to not buying their products. Machines which don't work cost money, time and patience. That adds up to a lack of goodwill towards a company which seems to have gone rogue in their quest for profit.

Mac Mini 2018 with 1 usb to DisplayPort monitor and 1 hdmi monitor. Hdmi monitor not working after Catalina upgrade.

Possible solution to the issue: Disconnecting the usb/Displayport cable at the Mini end and then rebooting solved it here.

Not sure since everything is working I don't want to retest! But disconnecting the usb/Displayport cable and rebooting with just the hdmi cable connected did not help. Disconnecting usb/Displayport at the monitor end and rebooting did not help. Only when I disconnected the usb monitor at the Mini end of the cable did the hdmi monitor start working again.

Same problems here. Working as graphic designer and got 2x 60Hz 4k Retina displays. The one connected with displayport to mac mini works. HDMI gets no Signal.

If you know a fix please let me know.

Greetings

Sven

You have to pay? To test THEIR products... that they make a profit off of? You have to PAY to find their bugs?! Whelp, guess when my machine dies I'm headed back to windows. If I'm going to spend hours trouble shooting I won't be paying $1000+ for the machine I'm trouble shooting!