Sony PCG-TR3AP - Manual (Page 171)

Why don't the Fn+F3 or the Fn+F4 key combinations work?
The Fn+F3 keys toggle the built-in speakers on and off. The Fn+F4 keys adjust the built-in speaker volume. The computer
may not recognize the Fn+F3 and Fn+F4 keys if the correct speakers are not selected. Follow these steps:
1. Right-click the Volume icon on the taskbar, and select Adjust Audio Properties.
2. On the Volume tab, click Advanced in the Speaker settings box. The Advanced Audio Properties window
appears.
3. On the Speakers tab, select the correct speaker setup from the Speaker setup drop-down menu.
Page 171