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I've got the two pieces of hardware above. For the dell m4800, it has the i7-4700mq and nvidia quadro k1100m running windows 8/10. Enabling or disabling switchable graphics from the bios doesn't solve the issue below:

When I plug the monitor via displayport directly to my laptop, the monitor is not detected, it never wakes up, and the laptop doesn't see anything. If I use a displayport to dvi adapter, the monitor is seen, but the max resolution is only 1280x720.

What do I do? I know the monitor works and so does the displayport cable, I plug it into another machine and I get my native 1440p resolution just fine.

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    This HR ZR2740W seems to be compatible only with some grphics hardware+drivers. On my old ThinkPad T60 (with ATI FireGL V5250) through DL-DVI on docking port, I get 1440 (Linux 3.16). On my new T450s with Ultra Dock, not detected via DP, detected only as 1280x720 via DVI (Linux 4.2.5). Another screen worked through DP via same cable. – alexei Dec 10 '15 at 4:06
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Since HP's cable is bloody expensive, you can add the pull-up inside the monitor itself. This allows it to work with any DP cable.

The pull-up that worked for me was 10k (even if the specs say it should be 100k - I tried and the monitor wasn't detected). Solder it between C278 (it's connected to DP pin 17, AUXn) and unfitted nearby resistor that goes to DP pin 20 (3.3V power).

Like this:

enter image description here

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    Attempted to solder 10K resistor, but it doesn't work. From the photo it looks like you've used 20K +-5% resistor. Will try that option – Woodman Mar 27 '17 at 9:57
  • unfortunately, neither 20K nor 30K or 40K helpd me. I would really appreciate if someone could give any ideas – Woodman Mar 28 '17 at 7:54
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You have to use a non-standard DisplayPort cable for HP ZR2740w: PN: HP 729896-001. I bought one from here and display was detected correctly with 2560x1440.

This note from Lenovo website applies:

The HP ZR2740w monitor requires a specific DisplayPort cable offered by HP in order to work with ThinkPad Pro/Ultra Docks and ThinkPad OneLink Pro Docks. This is due to a decision HP made with the internal design of the monitor. The special DisplayPort cable adds a resistor to the AUX signal which allows it to work properly.

Details from RichardJS about HP's mistake (aka. "design decision") in the monitor circuit:

The 729896-001 SPS-ASSY cable DP with AUX-N cable is a workaround for a resistor selection made in the ZR2740w monitor, on the DisplayPort AUX negative channel. The "pull-down" resistor used in the monitor AUX-negative channel is excessively "strong" in the parlance of electrical engineering, and causes the DP re-driver in the dock to remain in sleep (low power) mode.

This is because the DP signal re-driver in the dock monitors the AUX-negative voltage level to determine when a monitor is connected (which then causes it to wake up from low-power mode). The system DP port does not have a re-driver.

You'll have to review the DisplayPort specification from VESA for the AUX-N resistor value requirements on the source and sink, if you are so inclined.

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