I'm using an HP laptop with an external screen connected through an HDMI cable, and the lid closed.
Every time I lock the screen, it dims and then cuts signal to the screen, leaving it in a blue screen that says "No Signal", and eventually it just turns off.
I want to be able to lock my screen and walk away from the computer WITHOUT having the external screen turn off.
I have gone into Settings and unchecked "Dim screen to save power" and set "Turn screen off when inactive" to "Never"
I have run
I have gone into dconf-editor and set com->canonical->unity-greeter->idle-timeout to 0
No matter what I do, when I lock the screen (or it auto-locks), it dims and then turns off.