Latitude 7490 - Connecting second monitor through USB-C

Question

Hi, I have Latitude 7490 with thunderbolt mark near USB-c and I'm trying to connect to displays:  DELL S2716DG connected via DP to USB-C port and second old DELL U2410 connected via HDMI HDMI. The first monitor is detected in the system as Digital Display Dell S2716DG with default resolution 2560x1440 but it is black all the time. The second monitor work normally. I cross-checked the cables connecting U2410 using DP USB-c cable on res 1920x1200 and the second one on HDMI HDMI and that setup works fine. I've tried to change the resolution of S2716DB to 800x600 or any other with different refresh rates but all that didn't work. Any idea what can be wrong? I would like to take advantage of DP on my S2716DG since the signal going through USB-C is a native DP kind of signal.

Camelspk5 · Accepted Answer

Thanks for all the replies so far, I have tested with docking station WD19TB and this time I used normal DP-DP cables, and then DP splitter. To my surprise, it was working fine from latitude, but when I switch to my other computer with Geforce GTX 1080 Ti, the monitor started to blinking, it was showing the other desktop and going dark, and few times like that before eventually going dark for good. I have not found the actual reason but my guess is culprit was a faulty cable. Please close the thread.

DELL-Cares · Answer

Thank you! We have received the required details. We will work towards a resolution. In the meantime, you may also receive assistance or suggestions from the community members.

jphughan · Answer

@Camelspk5  Simple question first: Have you made sure to set your S2716DG to the correct input?  Sorry if that sounds trite, but that has been the answer in some other cases where I've helped people here.  But otherwise, this should be very simple.  The Latitude 7490 even WITHOUT Thunderbolt supports video output over USB-C, and if you want to use the DP input on your display, all you need is a USB-C to DP cable.  Normally I would have suggested another cable except that you say the cable works fine when using it with your U2410 on your system's USB-C output.  And when you say 'the second one on HDMI HDMI and that setup works fine', are you saying that connecting the S2716DG to the HDMI output using its HDMI input works?  If so, then unless it was a simple case of not being set on the correct input, based on your results it sounds like there may be an issue with your S2716DG's DP input connector.  However, if you can run the U2410 from USB-C using the USB-C to DP cable and the S2716DG from HDMI using a standard HDMI cable, then why is that setup not acceptable to you?  The HDMI output on the Latitude 7490 supports 2560x1440, so using the system's USB-C output or the display's DP input will not inherently work better.  Both of your displays support both DP and HDMI, and your system can run both of their displays at their full resolution using both methods, so even though it's strange that the S2716DG isn't working on USB-C, if swapping them around gives you a working setup, then that setup will work just as well.

Camelspk5 · Answer

Yes, it was connected to the correct input no worries. Well, I'd rather use my USB-C-DP cable for connection between my laptop and S2716DB because I have the second computer which uses DP-DP connection to that same monitor S2716DB and as you know DP might use 144Hz frequency and HDMI only 60Hz. I've got the 'DisplayPort 1.4 8K Bi-Direction switch' that I would like to use it for easy and quick switching the source of the signal given to DP input on S2716DB. It is not all about resolution and as I said the cable USB-C-DP works fine with U2410 so it is fine. DP input in S2716DB works fine as well because I use it for the other computer. My impression was that maybe for some reason my laptop doesn't have enough power to transmit signal from USB-C(TB) output to monitor with higher resolution than FULL HD. Might that be the reason? This is the only thing that differs between those two monitors.

jphughan · Answer

@Camelspk5  No it’s not a power or bandwidth issue. The earliest version of DisplayPort that was supported over USB-C was 1.2, which can carry 4K 60 Hz, so if you’ve got a USB-C to DP cable connected directly to the USB-C port, you should be able to use the full bandwidth of the port for video and therefore run 4K 60 Hz. Based on your results I’m not sure what to suggest other than maybe trying a different cable. That shouldn’t be necessary, but this also should be working and yet it isn’t.