Latitude 7390 2-in-1, WD15, two P2415Q

1. If we adjust the resolution down from 4K to a lower resolution, would the setup work? Please let me know if the setup I have requested would work if we lower the resolution. I do not care if the resolution is lower than 4K.

2. I do not see TB16 in the Dell online store. Would you please send me a link?

3. Using the devices I already have, is it possible to use both monitors? In other words, can we make use of both monitors, regardless of how they are connected directly or indirectly to the laptop and/or docking station? Please let me know. Thank you very much for your help.

The fault here is that the WD15 cannot support two monitor running at 4K. See this article, How to Use and Troubleshoot Dell Docking Station WD15. 

Connect the external power adapter to the other USB Type-C port on the Latitude 7390 2-in-1. Then retest.

Were these two P2415Q ever tested and working on a different PC in a daisy chain configuration?

Can you test both P2415Q HDMI in ports (one at a time) using the WD15 HDMI out port?

@Henry456  One quick note in addition to my reply above.  Don't use HDMI.  Running 4K 60 Hz requires HDMI 2.0, and the P2415Q is a 2015 model year display.  HDMI 2.0 didn't exist back then, so even if your Latitude supported HDMI 2.0, the display wouldn't.  And actually I don't think the Latitude 7390 supports HDMI 2.0 either since Dell normally specifies HDMI 2.0 in the specs when that's available, but the Latitude 7390's product page just says "HDMI", which normally means "HDMI 1.4" and is only good for 4K 30 Hz.

@Henry456  Your best case with your current hardware is still going to be terrible, for two reasons:

• When you daisy chain two P2415Q displays, each of them will be limited to 4K 30 Hz, not the standard 60 Hz.  30 Hz is not an acceptable experience for most users, since even the mouse cursor can look laggy.
• Due to the WD15's age and bandwidth limitations of USB-C, the WD15 can only run a single 4K 30 Hz display.  Stated differently, running dual P2415Q displays at their native resolution and refresh rate would require 4x more display bandwidth than the WD15 can tap into.

You need a Dell WD19TB instead.  It's a Thunderbolt 3 dock, which means that when paired with that system, it will tap into 4x more display bandwidth than the WD15 -- enough to run dual 4K 60 Hz.  Note that when paired with a Latitude 7390, which is a DisplayPort 1.2/HBR2 system, you'll need to connect one of the displays to the "downstream TB3" port at the edge of the dock, not to be confused with the USB-C port near the HDMI output.  You can use a USB-C to DisplayPort cable to make that connection.  The other display can be connected to one of the DisplayPort outputs.

I wrote an explainer post about the various operating modes of USB-C and TB3, with particular focus on the impact on possible display setups, over here if you want to learn more about why USB-C isn't going to work for you while Thunderbolt 3 will.

I would first disconnect the secondary P2415Q from the primary P2415Q. Then setup like this and set the primary P2415Q resolution to 1920x1080 60Hz in Windows Display settings =

WD15 cable --> Latitude 7390 2-in-1 USB Type-C port
WD15 mDP out port --> P2415Q mDP to DP cable --> P2415Q DP in port

Once that is working, connect the (turned off) secondary P2415Q to the primary P2415Q DP out port using the other P2415Q mDP to DP cable. On the primary P2415Q, enter the Menu OSD- Display. Set MST to Primary.

Turn the secondary P2415Q on, enter the Menu OSD- Display. Set MST to Secondary.

Then in Windows Display settings, set the secondary P2415Q to 1920x1080 60Hz.

Ok. I unplugged monitor 2 from monitor 1. As shown in the pictures I provided, the laptop is recognizing monitor 1. But Monitor 1 is stating "there is no signal coming from your computer". When I press the monitor menu button, the only menu I see is the Input Source menu, not any larger menu with other settings. When I close the laptop lid and reopen the lid, the laptop screen flickers continuously. Please advise. Thank you so much.

I have an HMDI cable. When I connect the laptop directly to monitor 1 using the HDMI cable, I *am* able to access the OSD on monitor 1. 

@Henry456  One other call-out for you.  If your 7390 does have Thunderbolt 3 and you get your hands on a WD19TB dock to run dual 4K 60 Hz, you'll need to remember to go back and disable that MST option on each of your displays.  When the MST option is set to either Primary or Secondary, the display limits itself to 4K 30 Hz to limit its bandwidth consumption to a level that makes a daisy chain possible, even when it's not actually cabled in a daisy chain setup.  The P2415Q will only run 4K 60 Hz when MST is set to Off/Disabled.  But just doing that right now with your current hardware won't get you 4K 60 Hz because that's being prevented by the massive display bandwidth shortage imposed by the WD15.

@DELL-Chris M Each of the two monitors successfully mirrors the laptop's display, when connected using an HDMI cable, using the HDMI port of the docking station and the HDMI port of each monitor. This shows that each monitor is able to function successfully, but this test setup involves one monitor being off (disconnected) while the other is on. My goal is to make both monitors work at the same time.

When each monitor is connected using HDMI, I am not able to change the MST settings in the OSD. The word "MST" is visible but darkened and cannot be selected. Would you please let me know what to do? Thank you. 

@jphughan Although using the dock is my preferred arrangement, I do not mind connecting multiple cables directly to the laptop, instead of buying an additional docking station. Please let me know if it is possible to achieve 4K on both monitors using the dock's ports AND/OR the laptop's ports. We can forget about trying to get a daisy chain to function successfully. Thank you.

The IT guy at my workplace is sending me a male-to-male DP cable and a keyboard. He said the male-to-male DP cable is required as the daisy chain cable. He said the keyboard is necessary because the laptop cannot be open while the monitors are displaying 4K, since the laptop screen is not 4K.

@Henry456  The MST option is grayed out when using HDMI because daisy chaining requires DisplayPort.  But again, daisy chaining is a bad idea in your case, so don't do it.  And using HDMI even with the display connected directly to the dock/system is also a bad idea because that particular display will be limited to 4K 30 Hz when using its HDMI input, so don't do that either.

Whether you can achieve dual 4K 60 Hz depends on whether your 7390 was ordered with the Thunderbolt 3 option.  I explained how to check that.

If your IT guy said that you have to keep the lid closed when running an external 4K display because your internal display is not 4K, he should be fired.  Windows can absolutely run different resolutions on each individual display, and even if that weren't the case, you can have a laptop lid open and set the built-in display to be disabled so that only the external displays are in use.  That is basic tech knowledge.

@DELL-Chris M These monitors are new and unused. No, I have not successfully tested them in a daisy chain arrangement using a different PC. At this point, I no longer want to try to make a daisy chain, as it apparently impossible without a newer laptop and/or newer docking station. Please let me know what cables and ports should I use, on the monitor and/or the docking station I already have, to use the two monitors I have? Ideally I would like to use 4K, if possible, but at this point I just want the two monitors to function adequately and simultaneously, regardless of which ports are used. Please advise.

@Henry456  I already told you how to get this working properly.  Any of these options will work, with varying quality of results:

• For best results, verify that you have Thunderbolt 3, and if so, get a Dell WD19TB and connect one display to the dock's downstream TB3 port using a USB-C to DP cable and the other display to one of the dock's DisplayPort outputs.  You'll have dual 4K 60 Hz, which is the ideal.
• If you don't have Thunderbolt 3 and you're NOT willing to give up on using a docking station, then the best you can achieve is dual 4K 30 Hz.  To achieve that, connect one display to the dock's MiniDP output and connect the other display directly to the system's HDMI output.
• If you don't have Thunderbolt 3 and ARE willing to give up on the dock, then you can have one display at 4K 60 Hz and the other display at 4K 30 Hz.  To do that, use a USB-C to DisplayPort cable to connect one display to the system's USB-C port, where you'll have 4K 60 Hz, and connect the other display to the system's HDMI output, where you'll have 4K 30 Hz.
• If you don't even care about 4K resolution, then you can connect both displays to your WD15 and set them both to 1920x1080, in which case you can run both displays at that resolution through the dock.  But you'll only be using 25% of the resolution that your displays can show.

@Henry456  Ok, sorry for the triple post here, but it appears that Thunderbolt 3 on the Latitude 7390 was optional, not standard.  The quickest way to tell would be to check the logo next to your system's USB-C port.  If it shows a Thunderbolt logo, then if you got a WD19TB you'd be able to run dual 4K 60 Hz displays, with both displays connected through the dock.  If on the other hand your system's USB-C port shows the "DP" DisplayPort logo, then it's a regular USB-C port that supports video output.  If that's what you have, then the WD19TB dock won't help you, because it will only be able to operate in USB-C backward compatibility mode, which with your system would be identical to the WD15.  And unfortunately in that case, you won't have a way to run dual 4K 60 Hz displays because you just don't have a way to get that much video bandwidth out of your system.  The USB-C port can run a single 4K 60 Hz display if you use it only for that purpose rather than for docking (see that explainer post I mentioned for more background), such as using a USB-C to DP cable to connect the display directly to that port.  But for your second display, if your HDMI output is only HDMI 1.4, then you can't run a second 4K 60 Hz display that way.  At that point the only option would be an USB dongle that uses "indirect display" technology like DisplayLink (not to be confused with DisplayPort).  That would technically work, but DisplayLink comes with some significant drawbacks.

And to address your earlier question, I really wouldn't recommend running your displays at lower than native resolution.  It won't look very good.  Running 1920x1080 would probably look best since in that case each pixel in the rendered image maps exactly onto a 2x2 physical pixel grid on the display, but if that's what you want, then you may as well just get 24" 1080p displays.

So, bottom line. Hopefully your Latitude 7390 has Thunderbolt 3 and getting a WD19TB is an option for you.

Thanks for the assist!

Can you test both P2415Q HDMI in ports (one at a time) using the WD15 HDMI out port?
* My thought there was testing the WD15 HDMI out port to the P2415Q HDMI in port just to verify that the P2415Q functioned at all. Which is why I asked if the two P2415Q worked in a daisy chain using another PC. Trying to isolate the failed devices.