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

I went on vacation for a week so I've missed this until now, but dual 4K 60 Hz from a WD19TB is possible if two conditions are satisfied.  First, the 7490 must have Thunderbolt 3, which is optional on the 7490.  Otherwise, the WD19TB will operate in USB-C backward compatibility mode, with the bandwidth limitations that entails, which on an HBR2 machine like the 7490 means dual displays only up to 1920x1200 at 60 Hz.  And second, one of the displays needs to be connected to the USB-C "upstream" port on the back of the dock.  This is all specified in the WD19TB manual, fyi, and I wrote a detailed thread about the display configuration limits of the WD19 family, including that port restriction for 4K 60 Hz, this thread if you're curious.

On the subject of that "upstream" USB-C port, whenever possible I recommend using USB-C to DisplayPort adapters/cables rather than USB-C to HDMI, for several reasons:

- All cables/adapters of former type will handle at least 4K 60 Hz, whereas only USB-C to HDMI 2.0 cables will handle the latter.  There are USB-C to HDMI 1.4 cables that might only do 1440p, for example.

- USB-C outputs provide a native DisplayPort signal anyway, which means USB-C to HDMI cables/adapters have to include a chip to actively convert that DisplayPort source signal to HDMI.  That's usually additional cost and always additional complexity.

- Some older 4K 60 Hz displays only accept 4K 60 Hz over their DisplayPort inputs anyway, because 4K 60 Hz only arrived with HDMI 2.0, which didn't arrive for quite a while after DisplayPort 1.2.

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@jimaah wrote:

Dual 4K 60Hz is not possible through the DisplayPort outputs on the Dell WD19TB dock. This I find odd to say the least as it's a step backwards from the older Dell TB16 dock with which you could get dual 4K 60 Hz via the DisplayPort outputs.

To get dual 4K 60Hz you'll either need to:

1. Buy a notebook that supports HBR3 (very niche right now)
2. Buy a USB-C to DP adapter to workaround this (your mileage may vary)
3. Buy a dock that supports dual 4K 60Hz without needing to do 1. or 2. such as the Dell D6000 https://www.dell.com/en-us/shop/dell-universal-dock-d6000/apd/452-bcyt/pc-accessories

 

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@jimaah  I agree that the port restriction on dual 4K 60 Hz seems odd, especially given that it didn't exist on the TB16, which is partly why I wrote the thread I linked in my post above to explain what's going on.  Your alternative options are all correct, but it's worth pointing out that the D6000 option carries a lot of other ramifications.  First, it will limit you to 60W charging, whereas the WD19 family can supply 90-130W depending on the system and the AC adapter wattage driving the dock itself.  And second, the D6000 uses a DisplayLink chip rather than native GPU output, which has a LOT of potential drawbacks that might affect people's use cases.  I wrote about those in this thread, specifically the post marked as the answer.  So yes, it might be a viable option for some, but that option should include some asterisks when it's mentioned.

User reported that both monitors came up properly at 4k this morning when plugging in the TB3 cable. The difference today is that he kept his laptop lid closed, so Windows detected two display devices (4k LG + 4k LG) instead of three (4k LG + 4k LG + Laptop screen).

The user reported that he did not need to push the power button on the Dock to wake his computer out of sleep and bring up the monitors. Just taking his sleeping laptop out of his laptop bag, and plugging in the cable was enough to do that, which I found a bit odd.

Anyway I'm going to keep an eye on this for another couple of days to see if he has any more unusual behavior.

@decker12  if your displays support HDR, then you wouldn't be able to run that color space with both 4K and 60 Hz also in use, because the bandwidth requirements of that setup exceeds a full DisplayPort 1.2 channel's capacity, and the 7490 only supports DisplayPort 1.2 (HBR2) output.  Some displays claim HDR support by deriving a faux HDR signal from an SDR signal, but if your display supports the actual HDR10 standard, then you'd need to either reduce your resolution or refresh rate to send it.  I suppose you could also reduce the chroma subsampling from the default 4:4:4 to something like 4:2:2 or 4:2:0, but I don't know if that option is implemented anywhere.

As for the cable length and power requirements question, I was actually curious when I read the WD19TB's specs indicating that the cable was now 0.8 m.  At first I thought it might have been an error in the documentation, but if you're finding that it is in fact longer than the TB16's, I guess there might have been advances in passive cable technology in the 4 years since the recalled TB15 (which was the basis for a slightly modified TB16) and today's WD19TB model.

@jphughan Thanks for that post! It was very helpful and increased my understanding of the WD19TB's output capabilities.

We're running it fine as your post and the manual recommended - HDMI to USB-C in the USB-C "Displayport" labeled port on the back of the WD19TB, and then a DP to USB-C plugged into the TB3 port on the back of the dock.

As soon as we ran that setup, both monitors lit up at 4k and 60hz.

As I posted earlier today, the only snag we saw in the past couple of days was that the user couldn't get one monitor out of 1080p when he plugged in with his laptop lid open. Windows 10 just didn't see anything higher than 1080p as an option unless I unplugged the HDMI cable from the monitor and plugged it back in, at which point it immediately went to 4k.

When the user came in today and plugged in with the laptop closed, both monitors lit up at 4k 60hz without a problem.

So far I'm tentatively optimistic that the right combination of cables and the WD19TB dock is going to be the solution to my multi monitor problem that the TB16 dock did not solve. I just hope the WD19TB is more reliable - as I said, I have a stack of six or seven TB16s that I'm going to e-waste because they've all died on me for one reason or another.

Unfortunately, the user has just reported the switch to 1080 on one monitor happening again. He unplugged his laptop, went to a meeting, came back with a closed laptop, plugged it into the dock, and 1 monitor popped up at 4k 60hz and the other popped up at 1080p without any option in the display settings to change it to 4k. 

This is how the user got it working again without having to unplug the HDMI cable from the back of the monitor, and it's a doozy. Something we definitely don't want our users having to do every time:

1) unplug dock, 2) open laptop screen, 3) close laptop screen (so it goes to sleep), 4) plug back in, 5) manually change resolution on monitor 2

I'm going to replace that HDMI to USB-C cable with another DP to USB-C cable to see if that fixes it. If not, I'm going to unfortunately have to return and write off our WD19TBs as we can't have our users screwing around like above when this problem happens. Sadly then I won't have any dual 4k docking solution. 

This is a one month old, all updated, 7490 with TB3 and Windows 10 so it's pretty close to out of the box. Monitors are also brand new.

I have thought it had something to do with the monitors, however we have several of the same monitors connecting to Macbook Pros using Caldigit TS3+ docks and those work fine at 4k and 60hz.

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@decker12 wrote:

Unfortunately, the user has just reported the switch to 1080 on one monitor happening again. He unplugged his laptop, went to a meeting, came back with a closed laptop, plugged it into the dock, and 1 monitor popped up at 4k 60hz and the other popped up at 1080p without any option in the display settings to change it to 4k. 

This is how the user got it working again without having to unplug the HDMI cable from the back of the monitor, and it's a doozy. Something we definitely don't want our users having to do every time:

1) unplug dock, 2) open laptop screen, 3) close laptop screen (so it goes to sleep), 4) plug back in, 5) manually change resolution on monitor 2

I'm going to replace that HDMI to USB-C cable with another DP to USB-C cable to see if that fixes it. If not, I'm going to unfortunately have to return and write off our WD19TBs as we can't have our users screwing around like above when this problem happens. Sadly then I won't have any dual 4k docking solution. 

This is a one month old, all updated, 7490 with TB3 and Windows 10 so it's pretty close to out of the box. Monitors are also brand new.

I have thought it had something to do with the monitors, however we have several of the same monitors connecting to Macbook Pros using Caldigit TS3+ docks and those work fine at 4k and 60hz.

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@decker12 i believe the issue you are encountering is due to the fact that the lcd screen is being opened. When this happens the graphics card detects this as third monitor and the system simply can't run three displays in the configuration that you want.

As @jphughan has mentioned the 7490 can only run HBR2. This is fine for running your dual display at 4K via the WD19TB, however if you add a third display i.e the LCD the highest resolution it can handle is 3 x QHD. I took this from the spec table in the article I linked to earlier - https://www.dell.com/support/article/us/en/04/sln316830/how-to-use-and-troubleshoot-dell-thunderbolt-docking-station-wd19tb?lang=en

The issue isn't with the dock itself, it's more the 7490 that isn't equipped to run 2 x 4K displays plus an additional third display.

Alan

@Dell-Alan D  I don't believe that's correct.  The triple display limitation to QHD on HBR2 applies to displays connected to the dock.  HBR2 and HBR3 refer to the bandwidth available over the USB-C/TB3 link, not the total system.  The built-in display has its own eDP interface to the GPU, other systems like the XPS 13 and 15 that have built-in 4K displays can run that display and dual 4K external displays all simultaneously, without any displays in mirror mode.  Dual 4K displays on the dock plus the built-in display should absolutely work.  Also, the post from @decker12 above indicated that the second display came up at 1080p while the laptop lid was closed, so the built-in display shouldn't have been a factor.  This sounds like it could be a driver or firmware glitch of some kind, either with the dock, system, or GPU.

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@Dell-Alan D wrote:

@jphughan that makes more sense as I run a dual display setup connected to my dock plus my laptop however it's not 4k. Normally I would suggest testing the system in the BIOS, but I don't think the system will output in 4K at a BIOS level or in the ePSA diagnostics. Would you agree?

Alan

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@Dell-Alan D  I haven't tested, but I suspect that's correct.  When I have external displays attached, my PC doesn't output to them at all until the Windows logon screen appears unless I have the lid closed.  And the additional complication with the WD19TB is that in the default configuration, Thunderbolt devices aren't even allowed to interact with the system until Windows loads.  Changing that would require you to enable Thunderbolt boot support, which allows any Thunderbolt devices attached at boot time to bypass the normal security routine.  And even then I'm not certain a dock would operate in an ePSA environment.  But based on @decker12's post indicating that seems is an issue that occurs when reconnecting to the dock but is ultimately fixable to the point that the displays all work as expected, I personally suspect a firmware issue.  The WD19TB is a new product after all, and firmware issues with new products are pretty much a given across the entire industry these days.

@jphughan that makes more sense as I run a dual display setup connected to my dock plus my laptop however it's not 4k. Normally I would suggest testing the system in the BIOS, but I don't think the system will output in 4K at a BIOS level or in the ePSA diagnostics. Would you agree?

Alan

@jphughan That is correct, the user did not have his laptop open when he plugged in the dock. Took laptop out of his bag which was in sleep mode, plugged in the cable with laptop closed, both monitors lit up after login, but the right side monitor was stuck at 1080. As I said , there was no option in Windows to change it until we physically unplugged the HDMI cable from the monitor. Windows 10 saw it as a monitor that had a max resolution of 1080.

What was also odd:

• He did not have to use the power button on the dock.
• He did not have to push a key to wake up the laptop (we have Wake on USB enabled in Power Management BIOS option turned on, which is not a factory default)
• Just the act of plugging in the TB3 cable woke it up.

I am waiting to hear from him if the replacement DP to USB-C cable has stopped this 1080p behavior.

This whole situation is very discouraging. We had such a nightmare of a time with the TB16 that no amount of firmware or installing drivers in the right order would fix it. Even the plastic on the TB3 connector snapped apart in every single one of our TB16s... just shoddy. The TB16 was garbage and we were only using 1080 monitors with them. It got to the point we just ate the cost of them and tried out 3rd party docks like the Caldigit TS3+, which work great for our Macs but have issues with our 7490s. I was really, really hoping we would have any issues with the new WD19TB, but so far that hasn't been the case.

As I said I'm not trying to do something crazy like daisy chain two TB3 hard drives along with a 4k projector and a 20' cable run to a TB3-enabled laptop made by HP. I'm using a modern, practically out of the box TB3-enabled 8th gen i7/16gb 7490 with Dell's latest dock and two brand new 4k monitors, with brand new cables, and it hasn't worked like it should. Thankfully the user is patient and not an executive or he'd be rightly **bleep** that every work day I'm back in there screwing around swapping cables.

If I can't get this super easy setup going, what on Earth is Dell using as test systems?

Funny you mention that, because I was just about to edit my previous message regarding a weird sleep state this same user is seeing with the WD19TB. He has both Wake on USB C and Wake on USB turned on in the BIOS.

When his 7490 goes to sleep after a period of inactivity such as the user goes to lunch, only one of the monitors will:

1. Go to sleep. Backlight turns off.
2. Wake up after 2 seconds. Backlight turns on, but no image on screen.
3. The monitor OSD says something to the effect of, "No signal detected. Entering power saver mode."
4. Monitor goes back to sleep. Backlight turns off.
5. Go back to step 2 and repeat every 5 seconds.

No idea why this is happening. I'll try disabling those options in BIOS and see. However, disabling those options - will the power button on the dock be the only method for waking the laptop up from sleep?

I doubt messing with BIOS settings will change the display behavior. My guess is that the sleep/no signal loop is triggered by some interaction between the display and the dock itself rather than a communication making it all the way back to the laptop, and therefore another firmware oddity of a new product. But that is purely a guess.

If you disable all of the other wake options, then the power button on the dock would be the only surefire way to wake the system back up. One additional method that would be available if the 7490 supports Connected Standby, which it probably does, would be to open the lid. I’ve noticed that my wife’s XPS 13 9350 wakes up when I do that, and I can’t find any way to disable it. I guess Dell (or Microsoft?) figures that if your system is asleep and the lid is closed, and then you open the lid, then you obviously want to start using your system again, and I suppose in the vast majority of cases that’s true.

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@decker12 wrote:

Funny you mention that, because I was just about to edit my previous message regarding a weird sleep state this same user is seeing with the WD19TB. He has both Wake on USB C and Wake on USB turned on in the BIOS.

When his 7490 goes to sleep after a period of inactivity such as the user goes to lunch, only one of the monitors will:

1. Go to sleep. Backlight turns off.
2. Wake up after 2 seconds. Backlight turns on, but no image on screen.
3. The monitor OSD says something to the effect of, "No signal detected. Entering power saver mode."
4. Monitor goes back to sleep. Backlight turns off.
5. Go back to step 2 and repeat every 5 seconds.

No idea why this is happening. I'll try disabling those options in BIOS and see. However, disabling those options - will the power button on the dock be the only method for waking the laptop up from sleep?

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@decker12 there isn't much further I can add that @jphughan has already explained in great detail. I await the results of the adaptor being tested to see where we go next.

There is a firmware update due in Aug 2019 for the WD19TB, the exact nature of the update I don't have access to yet.

What I will say though is in relation putting the laptop in a bag whilst in sleep mode. With the advent of Windows modern standby, we advise against putting any laptop to sleep before putting it in a bag. It must be powered down for this as modern standby can allow a system to be wakened with any type of system poll request. Something as simple as receiving an email can cause the system to wake and be powered on. As was mentioned above this can lead to battery drain but more seriously, overheating. A fried motherboard as a result of this would not be covered by warranty.

With regards to your wake issue, that is strange behaviour to have. I have a brand new 5490 as my work system with a dual display running via a WD15 with dual monitors connected via DP and mini DP. Most lunch times I will lock my system and after 15 mins it will go into sleep mode. I don't normally shut the screen as I have no need to. The way I wake my system is by pressing the power button on the laptop. The backlight will come on for say 15 - 20 seconds before the Windows 10 lock screen appears. There has been no mention of no signal found or any strange behaviour. The only time I encountered that behaviour was during initial setup and matching the inputs on the monitor for Windows and then detecting the monitors and setting them up for my desk layout. In the two weeks or so I have been using it in this configuration I haven't encountered any issues.

Alan