WD19TB - 7490 - Dual 4k at 60hz - Impossible?

@Sean Pitcher  the answer from @decker12  should get you running dual 4K 60 Hz.  As he noted, he's personally set this up.  The WD19TB manual that you can access by going to support.dell.com has a Display Resolution Table that indicates that if you want to run dual 4K 60 Hz, one of the displays has to be connected to the "upstream" Thunderbolt port located on its own on the far side of the dock, not to be confused with the USB-C output near the HDMI output.  A USB-C to DisplayPort cable is typically the easiest way to achieve that, although a USB-C to HDMI 2.0 cable would also work for displays that lack DisplayPort inputs, although your Dell displays would have them.  The remaining 4K 60 Hz display according to the documentation can use either of the DisplayPort outputs, or the HDMI output, or the USB-C output.

Only minor addition to @jphughan post above is that for connectivity, I use two of the same brand and length DP to USB-C cables. It's an extra expense, but that way the cables are interchangeable for whatever workstation I'm on. Plus I never have to worry about reaching into a pile of HDMI cables and getting some old-spec cable from 2010 which will drive me nuts troubelshooting.

Hi Alan

I just bough a new wd19tb and 2 dell u2720q, with each monitor I got DP port cables and also thunderbolt usb-c cables.

But no matter what configuration I try I cannot have dual 4k with 60hz on with 30 hz, according to what you said I should be able to use a display port in one and a usb-c in the other one.

my laptop is a dell Precision 5530 i9

Tks

Joao

@jchaveiro 

This link in this thread is what I use consistently to get dual 4k @ 60hz.

https://www.dell.com/community/Latitude/WD19TB-7490-Dual-4k-at-60hz-Impossible/m-p/7515179/highlight/true#M19691

Note that I am NOT using any of the DP ports on the back of the dock. To make this work, you need to use both USB-C ports. The cables are DP to USB-C and you'll need two of them, one for each monitor.

Your laptop has a Thunderbolt 3 port, correct? If it just has a regular USB-C port, that won't work.

@jchaveiro  If you're using a USB-C cable for one of them, make sure you've got it plugged into the "downstream" TB3 port at the far edge of the dock, NOT the USB-C output near the HDMI output.  The Precision 5530 is a TB3-capable DisplayPort HBR2 system, and as such if you want to run dual 4K 60 Hz, one of them has to be connected via that "downstream" TB3 port because of how the dock allocates display bandwidth received from TB3 HBR2 systems.  The other display according to documentation can be connected to any other port.  However, @decker12  deals with a lot of these docks and seems to have found that that isn't always the case.  In my view, real world experience is worth more than documentation every day of the week, because the tech world is filled with cases of things that SHOULD work but don't.  It's also filled with cases of incorrect documentation.  So if you've already got one display connected to that downstream TB3 port and another one connected via DisplayPort, then even though that SHOULD work with your system, I would recommend trying decker12's solution of using a pair of USB-C to DP cables, one connected to the downstream TB3 port and the other connected to the USB-C port near the HDMI output.

@mogmartin  Good tip!  Sounds like a driver/firmware issue though, since that shouldn't actually be necessary.  But of course the tech world is filled with things that are necessary that shouldn't be, which is why these forums are great to have....

This was invaluable, thank you - one thing to add having just been through it myself:

You MUST connect the USB-c version by itself, first, and set it to 4k 60hz.  THEN you can plug in the DP one and both have the frequency enabled.  If you have both plugged in during setup the 60hz option never became available to me.  (2020 XPS 15 7500)

Took me a while to figure it out hope it helps someone.

Thank you very much decker12. I have a similar setup to you with a 7400 and two 4k LGs. Was running at 30hz with the provided displayports and was driving me crazy. Bought the two CHOETECH USB-C to Displayport and I am at 60hz on both. Surprising that a dock retailing at $300 makes this process so difficult but what can you do. Really appreciate your dedication to this thread. 

@decker12  When TB3 just doesn't have enough bandwidth to satisfy the demands of everything, DisplayPort gets priority over PCIe.  But keep in mind that TB3 is 40 Gbps full duplex, i.e. in each direction simultaneously, and display traffic only runs one way.  So in your example of an external SSD, running dual 4K 60 Hz displays could conceivably bottleneck WRITE traffic going out to the disk, but it wouldn't bottleneck READ traffic coming in from it.  And this situation will be improved somewhat when DisplayPort DSC becomes more commonplace (unless people simply use that to run higher-end display setups rather than cut the bandwidth requirements of their existing display setups).

@knd0209 Great to hear it's working out for you. The thing that stinks about this solution is that you're in essence paying for a dock with dual THUNDERBOLT 3 ports, and using 18gb/s (4k @ 60hz) on each of them.

The other issue I've always wondered - and maybe @jphughan can chime in - is that dual 4k @ 60hz monitors take up 24 to 32gb/s of TB3 bandwidth out of a maximum of 40GB/s. Since you only have 1 TB bus on your laptop (ie the one place the TB3 cable from the dock plugs in), you only have 8 to 12 gb/s left for regular data. 

Plug in a couple of external USB hard drives and a HD webcam to the dock, and now you're easily hitting a data limit wall.

If you had additional TB3 peripherals (granted there aren't many), you wouldn't have anywhere on the dock (or on your laptop) to plug them in. Plus, their bandwidth would be severely compromised because there just isn't enough left in the TB3 bus after you plug in dual 4ks at 60hz.

Anyway, nothing to worry about because if you want dual 4ks @ 60hz you really don't have much other choice for this scenario.

Thanks for the suggestions and the nudge in the right direction!!!  I struggled with this also and actually gave up and was running one 4k display at 30Hz.  

End result: dual 4K display@60Hz from a Dell 7400:

Two Dell P2715Q 4K (old rev where only DP does 60Hz)

WD19TB Dock

Monitor 1--connected via Thunderbolt port on extended section of dock to DP on monitor

Monitor 2--connected via HDMI to DisplayPort adapter ((SIIG HDMI 2.0 to DisplayPort 1.2 Converter 4K@60Hz 4:4:4 HDMI to DP) which I purchased a couple years ago to try and solve this issue) DP adapter to DP on monitor.  

I only recently bought a 19TB dock I think this one is slightly newer and different to those already discussed.

This is to go with my XPS15 (8th gen i7, with the unusual Intel CPU + AMD GPU chip).

I don't seem to have the two usb-c ports on the other side of the dock mentioned above.

The main side of the dock (left long side if the cable is towards you) has power, network, two USB ports, a usb-c, an hdmi, and two displayport sockets. The right side has a single usb-c and a usb3.

The usb-c port on the main side will work, with a usb-c to hdmi adaptor, with 1440p@60, but is iffy at 4k and only does 30Hz. I can get the hdmi and displayport ports to work at 1440p60 but only 4k30, I tested various HDMI cables I had to check they were fast enough.

The usb-c on the other side of the dock, by itself with just a regular usb3 socket nearby, won't produce a detected monitor. Is this what decker12 said was a pass-through port or something?

I'm reluctant to buy a usb-c to hdmi cable, like those mentioned, unless I can be fairly sure it will work, the price isn't completely trivial, and I don't have a local computer store where I can buy one and take it back if it isn't to spec.

I have to admit, I am very disappointed that the dock doesn't do 4k60 out of the box. I nearly bought a TB16 but thought that the TB19 would be a better choice!

I have tried many different c

@speculatrix Do you have a Thunderbolt 3 port on your laptop? Not USB-C, but an actual TB3 port (which uses the USB-C style connector)? You will need TB3 on your laptop, otherwise your laptop won't be able to handle the required bandwidth that dual 4k @ 60hz requires. 

As I recommended in this thread a few times, I use two Choetec DP to USB-C cables. Monitor 1's DP port to the "USB-C Multifunction DisplayPort" on the back of the WD19TB (the one that's between the HDMI port and the USB3 ports). Monitor 2's DP port to the Thunderbolt3 port on the right side of the BACK of the WD19TB.

That is the only combination which has given me a rock solid, no screwing around, plug and play 4k @ 60hz on both monitors. Everything else - DP to HDMI, HDMI to USB-C, DP to DP, HDMI to HDMI - none of them worked.

If one monitor consistently doesn't give you 60hz, swap the ports out and see if it's a setting in the monitor that's preventing 60hz instead of a problem with the dock and/or laptop.

I have realised my mistake. I up the ordering, mine is not the TB dock. sorry for being a nuisance and a distraction. unfortunately I cannot delete or edit my previous post, sorry.

moderator/admin, please remove my post above.

I also ran into tons of issues and Dell support was not able to assist me at all with my configuration.  I finally tried a myriad of adapters and got the following to work 4k 60hz on both monitors and the laptop:

• 2 Dell 4k @60hz S3221QS
• WD19TB Dock
• XPS 15 7000 Series-7590

I connected both 4k monitors via their HDMI output plugs (Using direct DP connections was not an option for me).  For monitor 1 I used a DP1.4 adapter to HDMI adapter, the other I used a USB-C to HDMI adapter.  I directly connected monitor 1's HDMI cable to the right most DP1.4 port on the dock using the DP1.4 to HDMI adapter.  For monitor 2, I used a HDMI cable and a USB-C to HDMI adapter and connected it to the USB-C Left most port on the dock (NOT the middle port next to the HDMI 2.0 adapter).  This setup seems to get me both monitors working 4k @ 60hz without issues. 

Every time I tried either monitor connection using a direct HDMI dock port to HDMI on the monitor I could never get 4k @60hz.  If I connected one monitor directly to my laptop HDMI port I could get both working 4k @60hz.   I found this whole situation extremely strange and frustrating.  I don't understand why the docking station HDMI port doesn't work.  Dell's documentation seems to suggest that HDMI should work in combination with DP1.4 dual monitors 4k @60hz, but this does not seem to be the case.  No matter what I tried anything connect to HDMI directly would not work.  If I had another DP 1.4 to HDMI adapter I would be curious to give that a try to see if Dual DP1.4 to HDMI adapters would work, but I've already spent enough time and money on this frustrating effort.   Hopefully this helps someone else!