CSV-6400 not correctly detecting third HDMI Monitor

Updated on 06-06-2020 in MST Hub
3 on 26-05-2020



RTX 2070 (with latest driver 445.87 from today)
3x 1080p 60 Hz HDMI Monitor (identical models)

I just bought the CSV-6400 MST Hub and am currently going nuts.

When running any two monitors from the Hub (and the third directly from the GPU) everything works as expected. As soon as I plug the third Monitor into the Hub it gets detected, but only as a generic monitor (not by name like the other 2) that can only show 640×480. Forcing the monitor into another resolution from the nvida control panel results in a kind of  “upscaled” image.

The problem also is independant of the port on the Hub.

When having 2 “good” connections adding a third will result in the third one not being detected correctly.
When unplugging 1 “good” connection leaving 1 “good” and 1 “bad”, nothing changes (apart from one “good” screen going black).
When adding a third connection to 1 “good” and 1 “bad” connection, the new connection will work as intended with full resolution.

I also tried another USB cable than the one provided and tried 5 different power supplies (Mainboard, 2 Phone chargers, one Laptop Charger with additional USB Port and a Lenovo USB-PD supply with a Micro-USB Adapter).

I also added a USB Voltmeter in between, reading slightly above 5 Volts (depending on the powersupply used) and around 1.3-1.4 Amps with 3 Displays connected.

Currently no other Displays are connected for debugging reasons, but I want to connect a total of 5-6 devices in the end, though only the 3 monitors mentioned here are relevant to the problem.

The monitors were connected before with the used passive DP-HDMI cables and work flawlessly.

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0 on 27-05-2020

Hi When connecting the third screen and converting from DP to HDMI could you try an active Adapter instead of a passive? 


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0 on 02-06-2020

I’m still waiting for the active Adapter to be delivered, but I saw some new behavior over the weekend.

After starting the PC I still always have two working screens and one that’s not detected correctly. Though now most of the times when re-plugging the “bad” screen it gets detected correctly and I end up with all three screens working.

However today I booted the PC with only the screen attached that is most of the times the one not being detected correctly. After power on the screen was also not detected correctly, although having only one screen plugged in worked previously. The other two were detected correctly after plugging in and after replugging the first one it was also recognised by the system.

As far as I can tell, nothing has changed on my PC since I bought the splitter, apart from me updating the graphics drivers when first trying the splitter.

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0 on 06-06-2020


I tried with an active DP->HDMI adapter with the same result, but I might have found the real culprit.

I made some more tests with an additional monitor not connected to the hub and found the following: whenever the BIOS screen is shown on a monitor not connected to the hub, the screens connected to the hub work directly with full resolution.

Also when connecting any screen to a GPU port “before” (lower internal numbering?) the one the hub is connected to, the BIOS screen will show on this monitor with probably FullHD. However when the hub is the first screen to be used, the BIOS screen is shown on all connected monitors with a visibly lower resolution.

Makes partly sense as the BIOS is surely missing support for MST. However it seems that when the OS takes over, the hub switches to MST mode but keeps one of the screens on the “old” connection, therefore running on VGA.

I’m not really sure where to go from here, as this is either a problem with the Firmware, the BIOS, the OS or the GPU driver.

If you have any more ideas what to try or I can help to further debug the problem please let me know.

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