I tested this setup on an X230, which also has a DP output. That didn't work, either. I assumed the monitor's DVI input or the cable were bad -- until I tried setting the X230's BIOS display config to use DP during startup. Suddenly, the output worked -- until the boot sequence ended. Then it stopped.
This indicates that the DP output on the X230 works, the HDMI input on the monitor works, and the cable and adapter work. So why can't I see video after the machine boots?
I can't try this test on the X1. I was only able to get back into the X230's BIOS by connecting the monitor to an HDMI cable (my Pro Dock has an HDMI output). But the X1 and dock lack HDMI connections, so if I think I'll be unable to get back into the BIOS if I set the boot display to digital.
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