T420 Displayport

[Garth]

I'm trying to use the Display port on my T420. I have connected a hdmi/display port adapter to the port and a hdmi cable from this to a monitor but there appears to be no output. Windows does not appear to recognise that a monitor is connected. I'm using Windows 10 Pro. Has anyone got this to work?

[brchan]

Check for bad cables or adapters.

If yours has switchable graphics, then make sure the nvidia optimus drivers are working properly. The displayport on these particular models are wired to the discrete gpu. If you have the gpu setting to integrated, this port won't work.

[Garth]

Thanks for your help. Not sure what you mean about "switchable graphics" - mine has the Intel HD Graphics 3000 driving a 1600x900 display. Also the HDMI cable works (checked) and the HDMI/Displayport adaptor is new but could of course be faulty. Without buying another cable or adapter I have no way to check this as my other Thinkpads don't have a Displayport.

[Garth]

A friend has a Thinkpad T420 with a Displayport, Intel graphics and Windows 10. I've plugged the HDMI lead and adaptor into his T420 today and - same result as mine, i.e. Thinkpad doesn't detect the second monitor and it doesn't work. Unlikely therefore to be a physical problem with the port, unless this afflicts both our T420's.

Device driver problem? HDMI/displayport problem? Windows 10 problem? Has anyone had success with the T420 displayport and previous versions of Windows, with the Intel graphics?

[brchan]

https://support.lenovo.com/us/en/docume ... r-76686#21
Any motherboard with 'discrete' label will have switcable graphics.

Burn a linux 'live' distro (linux mint debian works great) to usb or dvd media. Go into the BIOS and there should be a config for graphics adapter. Set it to discrete and reboot. Press F12 after the reboot and select the usb or dvd drive to boot. Now check if the displayport works.

Booting from linux will help isolate whether this is a driver or hardware problem. This also avoids messing up the windows drivers if you don't properly uninstall and reinstall them before/after boot.

[kitor]

What resolution are you trying to set? Is Windows even recognizing connected display?

Displayport on Thinkpads has ++ mark, thus can use both active and passive DP-HDMI adapters (yes, they are two types, not every displayport can use passive one).
I sometimes use active DP-DVI adapter with my T420 and while it works on every DVI screen, with HDMI adapter I had problems with some screens.