2018 Mac Mini - monitor problems

I bought new 2018 mac mini a month ago and everything was fine hooked up HDMI to HDMI on my old HP 22cw 1080dp monitor. Bought Samsung U28E590D 4K a few weeks ago and my problems started. To get the best resolution had to go with USB C to Displayport. Running just the Samsung monitor had all the problems mentioned earlier when restarting and ended up on the start up screen. This would take 10-20 minutes. And stressed me out. My solution for now, till Apple comes up with a fix, was to hook back up the HP monitor, turn off the Samsung monitor and it boots up fine. So for me HDMI to HDMI works. It's seems to be USB C to DisplayPort where the problem is. By the way have no problems waking from sleep when running the Samsung monitor paired or singularly.

After I connect the new DVI - HDMI cable, tried to off night shift and also display detect as suggested in this forum, unfortunately nothing helped to solve my problem. However I figure out one work around to not disconnect and reconnect HDMI cable from Mac Mini every time from cold start. I used HDMI mini switch. This switch have one output and three inputs. It is enough to switch from port 1 to 2 and back. Basically it is the same as unplug / replug the cable. Hope that Apple will update the firmware soon and It will works as supposed to.

My insane solution...

This covers both "no monitor wake after sleep" and "no monitor display on cold boot."

1) Plug LG 4K monitor (HDMI 1.2) into old Apple USB-C to three ports (only one of which works at a time). Don't use that connection, because the resolutions available are limited and higher resolutions look bad.

2) Plug cheap, standard USB-C to DisplayPort cable into monitor and computer. Use this for the actual display by setting monitor to use the DisplayPort connection.

3) Keep second (HD) monitor on Mac's HDMI output.

I don't know why this combination works, but it does. It actually would work with Apple's display adapter, too, but that isn't really usable (visually). The Apple display adapter seems to calm the Mini 8,1 when it boots, and gets it all friendly, so it talks to the monitor via DisplayPort and the old HD monitor via HDMI.

Plugging the main monitor into the HDMI port results in "no wake on cold boot." Plugging the Sceptre (HD) into HDMI results in "no wake on cold boot." This combo works. I don't know why but all it costs is a useless adapter I paid too much for and never could use (it's rated all of one star on Apple's own store) and one USB-C port I wasn't using anyway.

I now have every single hole in the Mac Mini 8,1 filled, which is fun but might be a pain someday.... what's with the crazy high cost of USB-C to USB-C cables, anyway?

Although my trouble has been solved so far after update to Bata Catalina earlier. My problems were on an Asus monitor that got returned as it was new and wanted to rule out monitor was problem. Then it was still happening on my MSI monitor that I bought instead. So it was not LG for me.

Was on with UK tech support for a lengthly while this evening. It's now getting reported to engineering. The advisor did express the importance of everyone in this forum to come forward and create more awareness about this issue.

Pretty much the same story for me as other folks here: running a Mac Mini 2018 i3 with a LG 27UK650 over HDMI supporting 4k@60.

I had the issue on Mojave where it would wake from sleep with no display. On boot, *some of the time* the monitor just would not come on at all; I'd have to keep restarting to get into recovery mode and then it would OK.

Installed one of the Catalina betas after the advise on this forum and was thrilled that the issue had gone!

Then a new beta rolled out and the issue was back.

I've upgraded to the public release of 10.15 and it's still an issue.

Only way I can use my mac now is to plug in an old 1080p monitor I have, boot up, then switch the cable over!

I’ve had these display issues twice already. Six weeks ago Apple replace a whole motherboard due to I/O issues with display signal.

Half of my USB-C ports were not driving the monitors, HDMI was patchy and the rest had display artefacts.

Some monitors will not allow a patchy signal to even register, which is why they appear dead.

Yesterday all of a sudden the same issue happened again. After trying different cables, different ports, checking my display with a PC I concluded that the I/O are dead again (six weeks after replacement).

Out of curiosity I plugged my Mac mini to an old Sony Bravia HDTV and... everything works perfectly. No issues, signal is driven by all ports, sound is there, wake up is instant.

Looks like a compatibility issue between Apple hardware and desktop HDCP-ready displays, as I can’t see any other possibility if the hardware works fine on other devices such as TVs.

I'm updating now macOS to 10.15.1 and will see what happens. Not expecting anything but there must be something about Apple’s software implementation that drives the display crazy after a while.

if it’s Catalina, I might just reformat back to Mojave to see if this helps.

Apple support sent me a USB-C Multiport adapter to see if this would be a workaround and the monitor came up right away. Unfortunately, it only supports 30hz on the Mac Mini 2018. Don't know why the mini would be different but it is... https://support.apple.com/en-us/HT207806.

I also tried just leaving the adapter in with no HDMI connection to it and used a USB-C to displayPort adapter and the monitor came up fine again but pushed the refresh rate down to 30hz. No good, but maybe a single USB-C to HDMI port that supports 60hz might work or the issue could be all about the refresh rate.

USB-3 apparently gives off frequencies that are in the range of bluetooth. So, adequate shielding is required. Not sure if it's an issue with the USB devices themselves or inadequate shielding in the Mini. I suspect the latter.

I don't use the built-in USB-3 ports. I bought a USB-C to USB-3 adapter that I plug into the Mini that connects to my USB-3 hub that has a camera and my 2 external drives plugged in.

I was searching for any other answers I could find for this issue (I've had problems again following a reboot) and there's some compelling info at gpu.io:

https://egpu.io/forums/mac-setup/mac-mini-egpu-not-able-to-connect-direct-to-monitor/

https://egpu.io/forums/mac-setup/mac-mini-2018-no-display-after-a-reboot-or-coming-from-a-shutdown/

The recommendation is to reinstall macOS with your display connected directly to your Mac, and never install system updates with the display connected via the eGPU. The relevant bit of text comes from Apple's page on the Blackmagic eGPU:

Learn more

macOS currently doesn't support eGPUs in Windows using Boot Camp or when your Mac is in macOS Recovery, at FileVault login, or installing system updates.

I haven't tried a reinstallation yet but if and when I do, I'll report back.

Interesting. It changed and fixed EVERYTHING for me. I can boot with/without FileVault and get Apple logo and login. TB3-DP or HDMI-HDMI. Samsung 4K monitor.

Try SMC, NVRAM resets.

Try new install, not update. Need to make sure you startup security is set to allow external boot in order to do this.

I no longer have any issues but come to think of it, note that I always unplug my mini to eliminate any risk of power surges... per the above this would reset the pram. So handy

I had the same problem HDMI-USBc. The reason: you have to wait between 8-10 sec until it syncs. It's normal. It is not unusual. Read notes of cables in Amazon they explain that.

HDMI to HDMI is working fine for me since 10.15.2. I’m installing 10.15.3 and hoping they didn’t break it again while trying to fix it for other setups.

No change with 10.15.3 (LG 4K 27UK850, HDMI -> HDMI), back to Option-Command-P-R it is...

It worked for me. Do an SMC reset.