No HDMI signal after update

The HDMI issue on my 2018 Mac Mini using a 4K TV as a monitor was fixed with 10,15.1. After the update, I unplugged power to both the Mac and PC. When both powered on, HDMI 4K / 60 HZ worked fine, and has survived many power on/off cycles.

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.

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.

Had the same issue with a 4K monitor. I assumed it had locked up but I've just switched to a thunderbolt to DP cable and the update screen has returned...

same here very frustrated.

just upgrade to Catalina.

Mac Mini HDMI to Sony 65X9000E not work, no signal.

now use usb-c to hdmi : then ok

The best option for those impacted is a USB-C to HDMI cable. I've been using it for 2 days, and it's rock solid. The specific cable I'm using is

https://www.amazon.com/gp/product/B075V5JK36

That was a good idea. Just used that thinking with a usb-c adapter to hdmi which also worked. It seems bypassing hdmi is needed to get you back in to update. 2019 Mac mini.

In the end, I bought an HDMI/USB-C adapter with 4K support

Maybe this will help you to activate HDMI:

Changed monitor setting to "standard for monitor",

Shutdown MacMini,

Disconnect all monitor cables except HDMI,

Start the MacMini.

If it is set on Scaled the HDMI will not work.

Good luck!

Similar problem for me : mac mini connected to my old sony 65" TV ; was working fine with 10.14.

No display aft upgrade to 10.15.

It's work when connecting mac mini to an old 1080p.... quite disappointing; how do Apple test their new versions ???

I got the same issue with Mac Mini2018 with a Dell U2718Q Display.

I have to use a USB-C o HDMI adapter to get the signal. Yes, using an adapter works.

But, if you remove the HDMI from the adapter to the original HDMI port on mac mini, it stills get no signals.

I am just list the issues here, so Apple tech-team can get more devices tested before publish the OS.

I have had a lot of issues too, so far the only thing that works for me is DP to USB-C, both monitors work fine with that. I have two HDMI to USB-C cables I was using previously with Mojave but they do not work at all. HDMI to HDMI, not working although if I use my laptops USB-C dongle in the Mac mini and plug an HDMI to HDMI cable in via that it works fine...

I believe that the issue of the HDMI to USB-C cables not working could be the cables themselves, they are made by Benfei, the first set I got didn't work and they replaced them with ones that did, so I suspect they were flaky at the start. As it happen the DP to USB-C are also by Benfei but newer.

As a long time and avid Home Theatre enthusiast, and also someone who’s not into pop phrases, I just have to say that HDMI is far from a solid technology, and most who’ve worked with it for any amount of time consider it “a hot mess”. I am in no way saying this to excuse Apple from missing this problem, but breaking HDMI or at least crippling it, is pretty easy. The HDMI consortium creates a moving target to not only bring more advanced capabilities, but to allow manufacturers to sell new products; this puts us in a constant churn for new TVs, AVRs, UDPs, ATV, HD, UHD, 4K, 8K, HDR, Dolby Vision, Atmos, immersive audio, in a premium certified wonderland! Which is all to say it’s not bullet proof and $#!+ happens (again, I believe this should have been caught).

Someone had a theory that all of our minis were made on the same day, or had a unique part, or something else in common, there could be some merit to that. 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? Or rather something our monitors have in common in how they interact with the new minis HDMI? Looking for commonalities.

In the mean time I just received a USB-C to HDMI adapter (seemed I’d have more uses than a cable), and I can report another cheap workaround device for this HDMI issue. I’m hoping it’s a temporary solution as it now occupies my last USB-C port.

https://www.amazon.com/gp/product/B07JW7GT7H/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1

Resetting SMC and PRAM has resolved the problem of no connection being established with my Dell U2413 via HDMI - we will see if it lasts. The screen was recognised initially by the Mac mini after Catalina as installed, and then it stopped.

I was experimenting with Sidecar when the problem initially occurred and wondered if there might be a link - this seems (even?) less likely now - we will see. It looks as though the system could be corrupting the stored parameters in some way.