Sony PCG-R505GCK - Manual (Page 131)

Using Speakers
137
Why doesn’t my volume control dial work?
❑ You can also press Fn+F4 to increase the volume. If you double-click the
Volume icon
on the Windows® taskbar, you can view your changes on
the Volume Control window.
✍
The Volume icon and Fn+F4 shortcuts will work only when the volume dial
control is set to an audible level.