2018 Mac Mini second display troubles

[OppositeLock]

Hi All,

I've finally replaced my trusty 2008 Mac Pro with a 2018 Mac Mini. On my mac Pro, I had two Dell U2715H displays, running at 2580x1440@60Hz.

The 2018 Mac Mini has an HDMI port, which drives one of the displays just fine. I bought an Anker USB-C to HDMI adapter to connect the second display, and it doesn't work, the screen blinks on and off and loses sync. At lower resolutions, it works, but there's clearly signal noise, it looks like pink snow. I thought the adapter was bad, so I bought a generic one, same problem. Next, I bought the overpriced Apple Digital A/V multiport adapter, and it also exhibits the same problem! The display blinks on and off as it loses sync. WTF? I tried all three adapters on my Macbook Pro, and all three worked just fine at 2580x1440@60Hz, so this Mac Mini somehow fails to HDMI over USB-C.

Ok, HDMI doesn't work, so let's try displayport. I bought a USB-C to displayport adapter, and plugged it in, and it seems to work. However, the display now syncs at 59.88Hz, not 60Hz. The result is that you get subtle stutter in some smooth videos. So, while the monitor looks good on static images, playing movies is jerky.

The configuration I'm trying to run seems well within the specifications for this mac:
https://support.apple.com/en-us/HT209224

Any ideas as to why display adapters which work great in other macs fail to work in the Mac Mini?

 

[totoslack]

Do you have an external SSD like Samsung T5 connected?
I had the same issue. After I moved the first monitor from hdmi port to usb-c and disabled T5 encryption, everything is working fine.

Right now I have:
- for the first monitor ( Dell U2515H ) Apple USB-C HDMI multiport adapter.
- for the second one ( Dell U2515H ) Moshi USB-C HDMI adapter.
- I deactivated Samsung encryption for that T5.

 

[OppositeLock]

That is so random! No, I don't have an SSD connected, but I do have an OWC Thunderbay with several encrypted hard drives in it (the drives from my old Mac Pro). There's no difference if a disconnect it, though.

 

[totoslack]

Try also to change the cables.
I'm using these type of cables : Hama (HDMI -- HDMI)

 

[OppositeLock]

As a followup - I fixed it the problem.

It turns out that it was both the Anker USB-C to HDMI adapter and my HDMI cable degraded the signal. A better adapter mostly worked, and changing the cable mostly worked, but changing both out resulted in a happy second screen. The Apple Multi-AV adapter also doesn't work! These things are very sensitive to signal quality.

 

[Fishrrman]

OP wrote:
"It turns out that it was both the Anker USB-C to HDMI adapter and my HDMI cable degraded the signal. A better adapter mostly worked, and changing the cable mostly worked, but changing both out resulted in a happy second screen. The Apple Multi-AV adapter also doesn't work! These things are very sensitive to signal quality."

How about telling us WHICH cables you bought that worked?
With URLs, please.

 

[OppositeLock]

OP wrote:
"It turns out that it was both the Anker USB-C to HDMI adapter and my HDMI cable degraded the signal. A better adapter mostly worked, and changing the cable mostly worked, but changing both out resulted in a happy second screen. The Apple Multi-AV adapter also doesn't work! These things are very sensitive to signal quality."

How about telling us WHICH cables you bought that worked?
With URLs, please.

I used the Monoprice premium cables meant to do 4k@60Hz:
https://www.monoprice.com/product?p_id=15427

The replacement adapter is also an Anker, they were nice enough to send me another one.