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13533
March 2nd, 2019 19:00
U2719DC MST second display resolution
I have a Precision Mobile 5520 with Quadro M1200, and I have connected the laptop to the U2719DC via USBC/thunderbolt, enabled MST on the U2719DC, and have a U2717D as the third monitor (laptop, U2719DC, and U2717D). It took much futzing to get it to recognize the daisy chain U2717D, and it still doesn't work right.
For some reason I can't get anything beyond 1080x1024 on the U2717D - it shows monitor resolution different from the current signal resolution (see image), and the image is fuzzy. I have disabled the laptop display, so when connected to USB-C only the two external monitors are running. I've seen a few others post about this, but no solution. Is the second display on MST limited in resolution by spec, is my situation a graphics card limitation, or is something else wrong here?
Also, my monitors also show as being connected to the integrated Intel 630 graphics rather than the Quadro - shouldn't the monitors connect to Quadro, or is that a limitation of thunderbolt that they connect to the integrated graphics?
ToyotaCentury
4 Posts
1
March 9th, 2019 17:00
It looks to be impossible to run from laptop to monitor with USB-C to USB-C and use MST at anything higher than 1080p. The USB-C port on the Dell U2719DC is NOT thunderbolt 3, so therefore doesn't have the necessary bandwidth.
What you can do is connect from your laptop thunderbolt 3 port with a USB-C to display port cable, and MST works as expected since it functions in alt-mode Display Port 1.2 with just enough bandwidth to drive 2x 2560x1440. But then you miss all the benefits of the USB-C monitor - power and data connectivity to the monitor's USB ports will of course not work.
This is dumb. I probably will return my U2719DC and find a native thunderbolt 3 monitor. You only benefit from a USB-C monitor if you use 1 external display.
By the way, a great resource for all this ridiculously complicated USB-C / TB3 stuff is Startech, where I got my info:
https://blog.startech.com/post/thunderbolt-3-the-basics/
sfortin
2 Intern
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199 Posts
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March 5th, 2019 05:00
You can force the laptop to use the Nvidia GPU by going into BIOS and de-select "Switchable Graphics".
ToyotaCentury
4 Posts
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March 5th, 2019 19:00
Thanks for the reply, but my BIOS doesn't have that option. The second monitor in the MST daisy chain is limited to 1080p no matter what I do, and it's showing that it's using Intel 630 graphics rather than the Quadro.
ToyotaCentury
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March 8th, 2019 15:00
OK, some news. I was able to connect from my laptop USB-C to DP on the U2717D DP (MST On), and then to the U2719DC (MST Off) via DP to DP, and achieve the native resolution on my laptop (4k), and both external monitors (2560x1440).
After RTFM, the Dell U2719DC manual states that with USB-C to USB-C, a connection at HBR3 (graphics adapter link rate spec) is necessary, otherwise MST won't work, and advises to connect from USB-C (laptop) to DP (monitor) if your connection is HBR2 (which mine was). You find the link rate on the monitor menu, under display info.
My laptop is brand new, which is frustrating. I need to look at this more to see if there's not something wrong with the monitor itself.
pigmaster
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2 Posts
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March 3rd, 2020 05:00
We just had 20 monitors delivered, and the the problem that you have described occurred only on one. i have checked what you have said and yes it shows the lower rate. Besides these monitors support daisy chaining and we have tested that. So you can have one monitor connected with USB-C and second monitor connected to first one via DP. should work only with DP, tested on Dell Latitude 7390 with Core-i5-8350 and UHD Graphics 620.
Update, double checked the cable (the ones provided with monitor are pretty good quality but also they are bit stiff, so swapping the cable (180 degrees turn) on monitor's end fixed the problem with maximum resolution although the link rate still shows HBR2.