Dell Latitude 7490 WD19 Dock 3 Monitors

@DanJam123  when the WD19 is used with a system that provides an HBR2 signal (aka DisplayPort 1.2), which is the case with the 7490, it only has enough display bandwidth from the system to run two displays up to 1920x1200 or a single display at 2560x1600.  That's why you've got weird resolution limitations while trying to run 3 displays, and in fact I would bet that your 24" displays are supposed to be running at 1920x1080 rather than 1680x1050, so even that first display is very likely not "perfect".  These display setup limitations are all explained in the WD19 manual available on support.dell.com, fyi.

Additionally, when asking technical questions about display setups like this, it's much more important to indicate the resolution of the displays involved, not the physical size -- and specifically the "native resolution", i.e. the resolution they're supposed to be running, not the resolution you're currently experiencing.  Not all 24" and 27" displays use the same native resolution, and it doesn't matter to the system how large a display is, but it matters very much how many pixels you want to send to the display.  For the purposes of this answer, I'm assuming that your 24" displays are 1920x1080 and your 27" display is 2560x1440, since those are the most common, but if that's not correct, then my suggested alternative setups below may not be workable.

If you want to use three displays, then if your 7490 was ordered with Thunderbolt 3 support, which is optional on that model, the best solution would be to replace the WD19 with a WD19TB, which will be able to run your 3 displays because the WD19TB's use of Thunderbolt 3 means it can access 4x more display bandwidth than the WD19.  If your system doesn't have Thunderbolt 3, then these are your options for running 3 displays:

- Connect your 24" displays to the WD19 and connect your 27" display to the HDMI output on the system itself so that the 27" display's bandwidth requirements will not have to be met over the docking connection that doesn't have enough to run 3 displays.

- Use a dock that uses DisplayLink technology rather than tapping into native GPU output, such as the Dell D6000.  Using DisplayLink allows more bandwidth-intensive display setups, but it also introduces quite a few potential drawbacks that may or may not be acceptable for your use case.  I wrote about those in this thread, specifically the post marked as the answer.  The original question was about gaming, but my answer was broader than that.

If you're curious from a technical perspective about USB-C and Thunderbolt 3 in general, I wrote a thread explaining the various operating modes of USB-C and TB3 and their impact on possible display setups here.

Hi @jphughan 

I also have a problem setting up 3 displays (plus native laptop screen) on the WD19TB.

I have three identical P2419H screens (1920X1080), 2 connected to the WD19TB via display port and one via HDMI, laptop is a new Precision 5550, Nvidia Quadro t2000 + Intel UHD Graphics, any combination of 3 out of 4 displays works, i.e. if I go to display settings, one screen is disconnected, when I enable (extend desktop to this display) another display gets disabled. The exact same behaviour (any combination of 3/4 working) happens when I use the USB-C adapter shipped with the laptop and connect the HDMI screen directly to that.

Any help is much appreciated.

Hey@f.a.b.s , the behavior you're seeing is expected because on the Precision 5550, the Intel GPU has direct control of all display outputs, and Intel GPUs only support up to 3 simultaneous independent displays.  To run more than that natively from the GPU, you'd need a system where the discrete GPU had direct control of at least some of the display outputs, but that isn't the case on the Precision 5550.  So the only way to run more than 3 displays would be to run any displays beyond 3 via USB dongles that run "indirect display" technology like DisplayLink (not to be confused with DisplayPort).  Since they're not driven directly by the GPU, they don't count toward the GPU's maximum display limitation.  And since the video signal for them is transmitted as USB data, they don't count against available display bandwidth either.  Here is an example of that type of adapter.  However, the way DisplayLink works comes with some drawbacks that can be significant in certain use cases.  I wrote about those in detail in the post marked as the answer in this thread, so be aware of that.  If those drawbacks aren't acceptable and you require more than 4 displays, unfortunately you'll need a different system.  The Precision 7000 Series models have a BIOS option to allow the discrete GPU to take direct control of the display outputs, in which case you can run at least 4.

thanks a lot @jphughan 

An additional few questions:

1. The old laptop, XPS15 (XPS 15 7000 Series-7590) with the WD16 dock worked perfect for 3 + laptop monitor. As far as I can see from the hardware manager, the Intel graphics were the same.

Generally, if it is a problem with the laptop, I would really suggest for Dell to look into it or at least warn people prior to buying, this is their 2nd highest spec laptop and considered for pros and power users, and it can only run 2 external display?

@f.a.b.s  There is no WD16 dock.  There's a WD15 and a TB16.  But either way, the XPS 15 7590 does indeed have the same limitation, so the only way you would have been able to run 3 external displays with the laptop display simultaneously would be if one of the displays was connected through some "indirect display" dongle such as a DisplayLink adapter, which could have been plugged into the dock's USB port.  DisplayLink displays don't count toward the GPU's maximum display limit since they're not directly driven by the GPU, but the way DisplayLink works comes with some potentially significant drawbacks that I wrote about in the post marked as the answer in this thread.  The Dell D6000 uses DisplayLink technology, so maybe that's the dock you were thinking of?

I'm not sure it would completely practical for Dell to warn everyone about every possible spec before buying.  Based on my experience on this forum, lots of people ask questions that are already answered in documentation, so if people already don't bother to read information that's available to them, then piling on more information would just make it even more daunting for people to read.  Then there's the reality that even people running 3 displays are a tiny percentage of the overall population, and those running more than 3 are even smaller again.  But if you go to ark.intel.com to look at the specs of your CPU, which will include its GPU specs since the GPU is built into the CPU, you will find that it specifies 3 displays max.

@jphughan thanks again for your help/

Last question, will daisy-chaining work with a monitor capable of it?

@f.a.b.s  The dock itself allows daisy chaining, but the total bandwidth requirements of the daisy chain need to fit within what the single DisplayPort source interface can provide (and also what the system can provide to the dock, of course).  So for example if you're dealing with displays that only support daisy chaining at DP 1.2/HBR2 speeds, which is most displays right now, you would only be able to run a 2x 1440p daisy chain from a single DisplayPort output.  If you wanted to connect a third 1440p display, the XPS 15 would be able to send enough bandwidth to the dock to run that setup, and the dock can support it, but it wouldn't be able to push all of that bandwidth out of a single DisplayPort interface running at HBR2 speeds, so you'd have to connect the third 1440p display separately.

@f.a.b.s  The U2419HC is a 1080p display.  From a bandwidth perspective, you should be able to run a triple 1080p daisy chain all from a single DisplayPort output on the dock.  The reason I said "should" there is because the only time I personally ever tried to run a triple display daisy chain was with 3x U2415 displays that were connected to an E-Port Plus dock where I had a Latitude E5550 docked.  That never worked reliably even though it should have worked fine, so I ended up connecting a dual display daisy chain to DP #1 on the dock and the third display to DP #2.  But maybe drivers, firmware, and hardware have improved since then.  But if not, then yes your envisioned setup would be fine too.  You could even connect all 3 displays to the dock separately if desired.  However, no matter how you do that, you'd end up with all 3 displays driven by the GPU, which means you would not be able to keep the built-in display active with your system.  And you'd probably have to disable that before you'd be able to light up the third external display.

In terms of USB-C displays, I'm pretty sure you CANNOT feed a USB-C input from the DisplayPort MST/output of another one.  I think the USB-C input on a display needs to be fed by a native USB-C source in order to perform a USB-C link negotiation, which a regular DisplayPort source (such as a daisy chain output) wouldn't be able to do.  However, you could certainly connect the USB-C input directly to either the USB-C or "downstream TB3" ports on the WD19TB.  Or since USB-C displays typically also have a regular DisplayPort input, you could use that to allow the display to be in a daisy chain, or of course use that for a direct connection to the dock, either from a DP output or the USB-C/TB3 output using a suitable adapter/cable.

And if you have a system or dock directly connected to the USB-C input of a display and that display also has a DisplayPort output to start a daisy chain, then you can use that display as the START of a daisy chain setup.  However, depending on how the USB-C display configures the USB-C link, you might have reduced bandwidth available to use in that scenario.  For example, a 1440p USB-C display that has USB 3.0 ports integrated into it will typically configure the USB-C link to carry both video and USB 3.0, but carrying USB 3.0 simultaneously cuts available video bandwidth in half.  With DP 1.2/HBR2 systems, which is most systems on the market right now, that's enough bandwidth to run 1440p 60 Hz, so that's fine for a single display setup, but it wouldn't be enough to daisy chain much else.  The alternative would be for the display to configure the USB-C link to support full video bandwidth, which would allow dual 1440p, but in that configuration the USB-C link can only run USB 2.0 speeds, which may or may not be acceptable to you depending on what you plan to connect to the USB ports built into the display.  But not all displays allow you to choose how the display sets up the USB-C link in order to decide whether you want more video bandwidth or faster USB data rates.

As for the P2719HC, I really wouldn't recommend a 27" 1080p display for most use cases.  If you want a 27" display, you should really consider going 1440p.  A 27" 1080p display is just going to give you the same workspace that you'll have with your 24" 1080p displays, but spread out across a larger canvas -- which means that the image won't be as sharp.  27" 1080p displays make sense for kiosks where size matters more than sharpness and I guess for people that might have reduced eyesight and therefore would prefer to use extra display size to make a given image larger rather than adding more workspace (and they won't notice the sharpness reduction), but otherwise the pixel density of a 27" 1080p display is pretty low.  Just for context, Windows is designed around a reference pixel density of 96 ppi.  That means that if you had a 96 ppi display, then something that was meant to be an inch wide, such as an inch of the ruler in Microsoft Word, would actually be an inch as measured on the display itself.  A 24" 1080p display's pixel density is 94 ppi, pretty close to reference.  A 27" 1080p display drops that to 82.  By comparison, a 27" 1440p display gives you 108 ppi, which is a bit higher than reference, so it will look a bit sharper than even 24" 1080p.

@jphughan big thanks again!

So my ideal setup of three U2419HC (capable of daisy-chaining) should work using the WD19TB 2 display port outputs and one thunderbolt connection to my precision 5550 with 2 of the monitors in a DP daisy chain and one directly connected to the DP port of the dock?

Last last question, is a USB-C monitor an option as a third external display, so say my current setup with 2 external display, add a Dell 27 USB-C Monitor: P2719HC and connect via USB-C to either the laptop or the dock?

cheers and sorry again for my very limited knowledge

Hi and thanks again @jphughan 

So the only way to run 3 external monitors and the laptop display remains a second adapter/dock that uses DisplayLink technology?

cheers

@f.a.b.s  From laptops that have all outputs controlled by an Intel GPU as of this writing, that's correct.  Any displays beyond the third display (counting the built-in panel if active, or when running Linux where it's always active) need to be connected using something like a DisplayLink dock or dongle.  But if you have a WD19TB, you can just plug a DisplayLink dongle like this one into the USB 3.0 port of the dock.

@jphughan  - You're a genius, thank you. I have 3x 2560x1440 Philips monitors and for the life of me I couldn't get them to work on my Dell WD19TB, but adding the USBC-->Displayport connection and moving one of the monitors to it enabled me to get full resolution on all three monitors. I don't do a lot of graphics intensive work, so performance isn't the gotcha for me.. What I don't understand is why Dell couldn't manage to make a docking station that could handle the resoltuion. Seems like for what it is (and what it costs), This should have been capable of running three monitors at 4k if I wanted to.

@NettBeast  Glad I was able to help, although I'm not entirely sure what you ended up doing.  It sounds like you still have all three displays connected to the dock, but one of them is plugged into the "downstream TB3" port at the edge of the dock through a USB-C to DP cable?  Or did you connect one of the displays straight to your system to bypass the dock entirely?  If you did the former, then I don't understand your question about why Dell couldn't make a dock that could handle this resolution/setup.  If you've got all 3 displays running through the dock, then the dock IS handling that resolution/setup.  The WD19TB definitely supports triple QHD/1440p as long as it's connected to a system that supports TB3 rather than just regular USB-C.  However, the WD19TB does have some limitations around how displays can be connected, which relate to limited flexibility in terms of how it allocates display bandwidth.  If you want the really gory details, I wrote them up in an explainer post here.

As for triple 4K 60 Hz, that isn't possible due to bandwidth limitations on Thunderbolt 3, at least not without reporting to DisplayPort DSC, but that isn't widely supported yet, and I'm not sure the WD19TB supports it.  But without that, a triple 4K 60 Hz setup would require about 48 Gbps, which is well over TB3's 40 Gbps max even if you don't plan to leave any bandwidth available for data to run all non-display peripherals that are connected to the dock.

@jphughan 

Exactly that.  I found an older USB-C to Dual-Displayport adapter I used a while back before I had the dock, and yeah, I connected it to the downstream USBC port on the actual docking station.  

I had each monitor connected to the actual monitor port, two to the displayport connectors on the dock using displayport-->hdmi cables, and one to the hdmi connector using a standard hdmi cable.  When I was connected like that, I would get 2560x1440 on two of the monitors, and 1920x1080 on the third.  (They are 3 identical Philips 32" curved QHD monitors)

Didn't matter which one I set up as the low-res, it always had to be two and one.  So I found this bypass that you suggested for a different problem and tried it.  Apparently the way it's divvied up in the displayport means not QUITE enough bandwidth to go around, I'm not sure about how all that works.  Dug around to see if there was a firmware update for the Dock, didn't find one there, and that's where I hit the end of my expertise.  (I'm a Storage/SAN guy, only a PC Hobbyist)

FWIW, I run Ubunutu20 on a Precision 5330 laptop, and have the Thunderbolt port on the laptop set up in secure mode and had to specifically authorize the dock, if that tells you anything.

For now, it's working, and I'm not upset about it at all.  Like I said, I need real estate, not necessarily performance in this application, so the different performance of the third monitor doesn't really affect me as much.

(My gaming rig runs windows on an RTX2070 so has no issue with the monitors. )