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U2520D, Lenovo Yoga Slim, USB Type-C, no signal
Hi,
i recently purchased a Dell U2520D Monitor. However, it refuses to properly work when connected via USB-C. I am using the Monitor with a Lenovo Yoga Slim 7 15, which has an integrated Intel GPU and a dedicated Nvidia GTX 1650 GPU. My plan was to plug in the monitor to the USB-C port, so I could use the USB ports of the monitor for keyboard, mouse etc. The Yoga Slim 7 supports DisplayPort Alt Mode 1.4 via USB-C, as far as I know.
However, whenever I am trying to connect the monitor via USB-C it randomly loses connection and sometimes even restarts. This happens especially when exiting or sometimes starting a game that uses the Nvidia GPU, so I suspect that the connection loss has something to do with the switching between igpu and dgpu. I updated all the drivers, used different cables etc, but I still cant find a solution.
I also tried plugging in a HDMI Cable and the USB C cable at the same time, hoping that the display signal would be transported via HDMI and the USB C cable would take care of charging and data connection. That did not work either and randomly resulted in a loss of connection or a black screen or the notebook rebooting. There's something wrong with the USB C drivers/connection.
The monitor works fine when connected via HDMI - however, like this I cannot use the monitors USB C ports, nor can I charge the notebook via USB C, which kind of misses the point of USB-C monitor.
Could anyone help me out with this issue? Help would be much appreciated!
de_laune
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January 4th, 2021 12:00
After trying for a couple of hours, I finally managed to solve the problem: I just had to enable MST (Multi Stream Transport) in the monitors settings!
I still dont get why this particular setting caused so many problems... If someone has further information feel free to explain
jphughan
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January 4th, 2021 12:00
@de_laune My only theory, which may be completely implausible for a reason I'll get to, has to do with the fact that MST requires at least DisplayPort 1.2 support, so whenever it's enabled, the display has to operate using at least that revision, which means the source system has to support at least that revision. But a single QHD 60 Hz display can be run using only DP 1.1a bandwidth levels, so if MST capabilities aren't needed and therefore are kept disabled, some QHD and lower displays will operate as DP 1.1a displays for maximum compatibility with source systems. But the reason I'm not sure that's plausible in this specific case is that you're using the display's USB-C input, and the earliest DisplayPort revision that was ever supported to be carried over USB-C is DP 1.2. So even if keeping MST disabled caused that display to operate in DP 1.1a mode for its DisplayPort input, I'm not sure it would have been possible or at least "legal" for it to attempt DP 1.1a mode on its USB-C input that you were using. And of course even if it WAS doing that, a newer system that supports newer DP revisions shouldn't have a problem using older standards. But I guess the key word there is "shouldn't". But again, this is just a theory.
jphughan
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14K Posts
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January 4th, 2021 12:00
@de_laune Glad you're sorted, although that's an odd fix. MST is normally only enabled when you're daisy chaining another display onto that one, because that's the purpose of that feature. But obviously having the display operate in a way that advertised that capability to the system somehow worked around a quirk. There's no harm leaving it on even if you're not using it, so I guess just enjoy your newly functioning setup!
de_laune
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January 4th, 2021 12:00
@jphughanThanks! Now I can finally enjoy the full capability of this monitor.
Its exactely like you said: I actually didnt even look at the MST function at first, thinking that it would only help for daisy chaining. Turns out you sometimes have to look at the unlikeliest of all options when troubleshooting.
Glard to hear that leaving MST on does not mean any harm.
Not sure what exactly happened when enabling MST though - I would really be curious to hear some theories
de_laune
5 Posts
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January 4th, 2021 12:00
Alright, that sounds rather plausible. Thanks for the explanation