I've got a Pi3 running 4.9.35-v7+ #1014 SMP. For some reason, when left unattended the screensaver turns on but the display never enters power save mode. I have to shut it off with the power switch. Needless to add, I'm inclined to forget....
The display does power down using the experimental GL driver, but that's not practically usable, however it suggests the cable and hardware are OK.
The power manager settings are never sleep (to preserve the Wifi connection), blank after 2 minutes, sleep after 3 minutes and switch off after 4 minutes.
Is there a setting I've got wrong or don't know about?
Thanks for reading,
bob prohaska