Screen flickering with Minisforum NAB6 - Is it my monitor fault?

[Laurent_Gosselin]

Hi there,

I bought a Minisforum NAB6 (Minisforum NAB6/NPB7) two weeks ago. In Europe, the performance per euro made really sense.

Initially I intended to use it as replacement for my aging laptop. Since it has two USB-C port able to carry DisplayPort, I thought I could simply use a dock at work and at home and just worry about bringing power since unfortunately it cannot be powered over the USB-C port. So only 2 cables to (un)plug when switching between home and office.

My monitors setup is a Dell 27" U2721DE 1440p and an Asustek Pro Art 27" PA278QV 1440p. The Dell has an integrated dock which is setup to act as a MST hub. It forwards DP signal to the Asustek. It works fine with my old laptop with its 8th gen CPU. The only thing to do is to downgrade the USB connectivity to USB 2.0 to recover enough lanes to be able to drive the two monitors at 1440p. (8th gen CPU is DP 1.2 and speaks HBR2).

With the NAB6, I have access to DP 1.4 HBR3 and could potentially keep USB 3.1 speed while driving the two screens at full resolution. Since I might still use my laptop, I will probably keep the priority on data resolution and leave the USB part set to 2.0.

The main issue with the minisforum is screen flickering. The screen would show a good image (ie. readable, expected resolution) for a few seconds, then the screen turns black and the monitor proceeds looking after signal. Usually it will find it back and display again the image for a few seconds. Both screens flickers independently at their own pace. The Asustek will usually go to sleep after a few attempt. The Dell monitor goes may or may not go to sleep complaining there is no signal on the USB-C.

I have been lucky a few times to have a stable image on both monitors for more than an half an hour. So it looks like it should work but I can’t reproduce that kind of stability reliably, which is annoying if I intend to have productive work done. But hey, testing is fun!

Turning off MST allows me to have a stable experience, but my second monitor is now a simple mirror of the first.

I tried Ubuntu 23.04 live cd, Ubuntu 22.04 LTS installed and up-to-date, and Win 11 installed. All the OSes exhibit the same instability, even when only the Dell screen is on (MST enabled) and the other one off.

Under linux, is there a place where I could look to understand what is going on and if I can have some hope of fixing this via software? Is there some diagnostics I could run to get a clear picture (no pun intended) of what is wrong in the chain? (display port link training, modelines, buggy MST hub, uncooperative Asus Pro Art, …)

Is there a way to downgrade to HBR2 just for testing? (Since my laptop can make this setup work with DP 1.2, I might very well settle for that)

Thank you in advance for any suggestion,
Laurent

[wizarddata]

The simplest solution might be to try replacing cables, smells a lot like a signal integrity issue to me.

[wendell]

Almost certainly cable integrity. Try Moshi USBC to dp. Almost all USBC to dp cables are only tested for 1080p60 and Allie even if they’re not

[Laurent_Gosselin]

Thx for the replies!

Currently I’m connected like so:
NAB6 -USB-C ----- USB-C -> Dell 27" -DP ----- DP-> Asustek 27"

I can indeed try another DP-DP cable for connection between the two monitors and see if it helps. I hope to be able to borrow one or two from work this week. I was kind of hoping that a single 1440p signal was not very hard to achieve, even for a (potentially) crappy cable.

On the USB-C - USB-C front, I guess that increased data rate due to HBR3 is testing the limits (and quality) of the cable provided by Dell. Do you have a recommendation for a brand of cables that usually are ok for high data rate? (Darn that 5000$ cable tester could be handy)

Otherwise, any chance that I can instruct somehow the graphics card to work in HBR2? That would lower the data rate on the cable which is known to work at that rate. I can’t find any information on the web about that.

[Laurent_Gosselin]

I bought two USB-C - USB-C cables to replace mine. Spoiler: One works!

My initial guess was to go for a cable rated for USB 4 & Thunderbolt 4 at 40 Gbps. I figured that if I took a cable with a high speed rating it could handle anything I have to throw at it since I don’t need all that bandwidth. Oooh I was so wrong…

At the same time I bought a second cable rated for USB-C 3.2 gen 2x2 20 Gbps at almost half the price of the first, just to try and have a second option. Good call!

The end result is that the 40 Gbps cable does not work (not able to have two screens on, not even in a flickering state, I would say it might be worse than my original cable). With the 20 Gbps cable, no problem. I can even enable a USB 3.1 link with my two screens 2K@60Hz on. This is the way!

I’d love to get technical information. (Is it a good idea for a video?) Did I buy a poor 40 Gbps cable and a good 20 Gbps cable? Or is there a difference at PHY level that could explain it?

Something along the line of a data encoding for USB4/Thunderbolt 4 made to cause less interference thus requiring less shielding and can accommodate lower quality conductors, whereas for raw USB signal found in USB <= 3.2 would be more picky with cable quality? Is that even a possible explanation?

Anyway, thanks for making me pursue the signal integrity idea. And please chime in with PHY/encoding/cable rating comments.

[peatrick]

Glad you were able to resolve your issues. I just decided to take a chance on one of these NAB6 (32GB, 1TB) for a budget workstation, but having a heck of a time trying to get 1440p @60Hz out of Win11 Pro with the built in graphics. Sorry to piggyback on your message, Reddit has become a bit of a cesspool as far as technical assistance.

Probably should (i did) start my own post, but i’m curious how your overall experience has been with the intel Minisforum NAB6. Not being able to run my dual 1440p displays (currently at 1080p) is going to become a dealbreaker real fast, oof. Hopefully it’s PEBKAC and nothing more. Will keep tinkering, just got it unboxed.