After rebooting, my monitor will eventually get no signal after letting the computer idle for a while, typically around 20 minutes. To get this to stop happening, I have to go to power management, check the box that says screen energy settings, hit apply, then turn the box back off and hit apply again. It resets after rebooting.
Does this still happen with 4.9.3 or later? It sounds like it could be bug 295164.
OK, duping to 295164. I hope that your screen blanking or screen saving woes really are at an end.
*** This bug has been marked as a duplicate of bug 295164 ***