Windows 10: On lock screen, 2nd monitor does not recover from power-saving mode

(Workaround is in place for this issue, but I want to leave some notes here in case I start looking at it again.)

OS: Windows 10 Pro 64-bit
GPU: NVidia GeForce GTX 750
GPU Driver:
Monitors: LG Flatron w1942TQ (primary), HP w1907 (secondary)

Setup: Windows 10 Desktop PC. Two monitors connected to video card in one of the following ways:

A) Video Card HDMI -> HDMI-to-DVI cable -> Monitor DVI
B) Video Card DVI -> DVI cable -> Monitor DVI
C) Video Card DVI -> DVI-to-VGA adapter, VGA cable -> Monitor VGA

I would prefer option A for contributing the least amount of physical bulk to the cabling of my system.

Problem: When locking the screen (Win+L), the monitors will go to sleep after some time has passed to save power. Upon hitting a key or moving the mouse, both monitors should wake up. When connected via DVI or HDMI-to-DVI, the second monitor will not recover until it is powered off and on again by hand.

When connected with a DVI-to-VGA converter, the second monitor recovers as expected.

Next Actions: Currently I’m using DVI-to-VGA for the secondary monitor. Another option might be to make a registry modification to disable monitor sleep on the lock screen entirely (which I haven’t tried, but someone wrote up the instructions here.)

I’m just curious why it doesn’t work with a digital signal… I haven’t done enough testing to pin down what’s at fault. I updated GPU drivers, but haven’t checked for new BIOS/UEFI versions, haven’t tested with another HDMI monitor, and haven’t swapped the primary/secondary designation for the two monitors. Had enough for today, and there are better things to do to prepare for the new year. Will update if I learn more about what’s going on.

11 Nov 2017 — Currently using Fedora 26, and the same behavior is present. I found an option in the HP w1907 which prevents the monitor from going to sleep while no signal is detected. (Management… -> Power Saver -> Off.) This prevents the issue, but leaves an annoying “Check Signal Cable” test message that ping-pongs across the display, until either the PC starts providing signal again, or you turn the monitor off. Using an analog VGA cable is still a better solution, since the PC is still able to wake this monitor back up following going to sleep.

Maybe analog VGA has some capacity to wake up a monitor that digital DVI/HDMI is lacking.

(e: 11/Nov/2017: updates)

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