In the current version of the new Raspberry Pi mirror 2019-04-08-raspbian-stretch.img, you need to use the following method is prohibited screen sleep:
south you /etc/lightdm/lightdm.conf
Uncomment them
#xserver-command=X
And revised to
xserver-command=X -s 0 -dpms
-s # - Set the screen saver is not enabled
dpms turn off the power saving management
restart Raspberry Pi
sudo reboot