Here's my problem: I had Ubuntu 8.04 on this Notebook Asus 1015 px and the combination fn + f7 worked well and I could turn on/off the display at my leisure. Then I formatted and started a "new adventure" with Ubuntu 14.04 but now fn+f7 no longer works! It was a really useful option, especially when I have to take notes during the lessons... Anybody can tell me why? I've lost all hope, internet researches have been a waterhole! Thanks a lot.
You can try setting a shortcut in keyboard settings. Go to System Settings > Keyboard and click on the Shortcuts tabs. Click on Custom Shortcuts and then click on the + (plus) symbol. Give the shortcut a name and in the command section add
xset dpms force off
This command switches the LCD off until you move the mouse or press a key, just like when the laptop is left idle.
Now here is the bit that may or may not work: Click on your new shortcut where it says Disabled and press your key combination FN + F7. Hopefully it will recognise the combination and FN + F7 will now execute the command to switch the LCD off.