DisplayPort doesn't work on PR03X with E7470

Question

Hello everyone.

I have E7470 docked on PR03X and I need to connect my HDMI monitor via DP in PR03X, but it's not detected by my system (W10x64). I don't have this issue with VGA/DSUB and integrated HDMI in E7470, but somehow my laptop cannot recognize my monitor when I'm trying to use external DP. I have two different cables and even I bought new more powerful AC adapter, 130W model PA-4E, recommended for this dock station.

Can you help me? I keep my drivers updated, but maybe somehow I missed something, or anything else I messed up.

jphughan · Accepted Answer

@JacaC8 If the display's resolution is 1920x1200 or lower, try using a DVI to HDMI adapter instead, which is a simpler setup. DisplayPort to HDMI requires an actual signal conversion since DisplayPort and HDMI aren't just differently shaped connectors but completely different signal types. DVI and HDMI up to 1920x1200 are identical signals at an electrical level.

If your display's resolution is greater than 1920x1200, then a typical passive DisplayPort to HDMI adapter won't work, but an active adapter probably would, and it might even work around this problem with lower resolution displays if the DVI to HDMI option doesn't work. Passive DP to HDMI adapters rely on the source system supporting "Dual Mode DisplayPort", which allows the source to switch to native HDMI signaling rather than DisplayPort. But it's fairly common for the maximum resolution in HDMI signaling mode to be lower than when using native DisplayPort, partly because the HDMI spec has always lagged behind the contemporary DisplayPort spec. And I'm 95% certain that the HDMI spec supported by that dock's DP outputs limits resolution to 1920x1200 in HDMI mode. By comparison, an active adapter allows the source to continue using DisplayPort signaling, thus allowing higher resolutions, because a chip within the adapter performs the conversion to HDMI, and newer adapters would support newer revisions of HDMI that can support outputting higher resolutions in HDMI mode.

Also, does disconnecting the VGA display make a difference? Depending on the resolution(s) of the display(s) you're trying to run, which you didn't specify, you might not have enough bandwidth from the system be able to run your particular combination of displays. Another factor there is whether you have a first or second generation dock. Unfortunately Dell used the PR03X code across both generations and even between the E-Port and E-Port Plus variants, the latter of which have dual DisplayPort outputs. The reason THAT can matter is that the first generation docks only operate in DisplayPort 1.1a mode, whereas the second generation supports DisplayPort 1.2, which supports much higher bandwidth both from the system and out from the DisplayPort output.

If none of that works, do you possibly have a display with an actual DisplayPort input you can test just to verify that the DisplayPort output is working at all, without relying on an HDMI conversion by the dock or an active adapter?

JacaC8 · Answer

Thank You for quick respond. I'm trying to run 1920x1080 and disconnecting VGA doesn't help. Unfortunately I don't have display with DP input, so I gonna try, as You said, with DVI - HDMI.
Thanks again.

I'll let know if this will help.

jphughan · Answer

@JacaC8  Actually I thought of one other thing. Try updating the firmware of the MST hub chip in the system, since one of the updates increased compatibility with those adapters when used with docking stations. You have to run this update while the system is connected to the dock AND a display connected to the dock is active, so make sure that VGA display is in use. The latest MST chip firmware update as if this writing is here: https://www.dell.com/support/home/en-us/drivers/driversdetails?driverid=djg3x&oscode=wb64a&productcode=latitude-e7470-ultrabook

JacaC8 · Answer

It did not help ;/ Waiting for DVI cable.

JacaC8 · Answer

Ok, I used DVI-D (18+1) - HDMI and it works, even though Dock Station is not powered.

So if I understood everything good, Display Port should works fine with greater resolution (unfortunately I don't have anything to check this) or DVI-D dual link (24+1) should be enough?

I'm just curious. I only needed sound transmission via monitor straight to speakers. I was using Bluetooth, what was uncomfortable.

jphughan · Answer

@JacaC8 Why is your dock not powered? That isn’t a supported setup. You’re supposed to have a 130W adapter connected to the dock, then you dock your system and it charges through the dock, AND the dock has power to run its internal electronics properly.

The dock doesn’t support dual link DVI. The most you’ll get there is 1920x1200. DP on a first gen dock will do 2560x1440 60 Hz or 4K 30 Hz. DP on a second gen dock can do 4K 60 Hz.

JacaC8 · Answer

It's not supported but it works fine not power, not mention 90W adapter. I bought 130W and I don't see difference, but for now i don't use eSATA or any other high energy consuming HW like usb HDD. I consider to return this power adapter.

jphughan · Answer

@JacaC8  Ok, well going forward, if you're running your equipment in an unsupported configuration, it would be good to mention that upfront.  Not mentioning that type of information could cause troubleshooting to go down the wrong direction for a while, so if you only mention it later on, it can be frustrating to the person who was helping you if that information would have revealed the solution much sooner if you had mentioned it much sooner.  I was wondering if not powering the dock might have affected its DP outputs somehow, but maybe not.  Still, I don't really see why you wouldn't power the dock.  The point of a docking station is to allow you to just dock your laptop and have everything you need instead of having to and disconnect connect cables directly on your laptop as you come and go.  But if your dock doesn't have power, then you need to dock your laptop and then connect/disconnect power separately.

JacaC8 · Answer

I did not mention that before cause I use dock station with power adapter, but anyway it can run even not powered. I specially bought new power adapter 130W, cause I did suspect that maybe my 90W adapter cannot run Display Port properly. As I mentioned it didn't not help, so I asked here for help.

In conclusion, I can't get image by using DP - HDMI cable connected to DS (powered by genuine PA-4E 130W adapter) - TV. But DVI-D (18+1) works great.

Latitude

DisplayPort doesn't work on PR03X with E7470

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