Sony PCG-F420 Primary User Manual page 62

When you connect an external display to the monitor connector, you can
toggle the output between the Liquid Crystal Display (LCD), the external
monitor, or both devices.
Use the keys to select a display. See also "Selecting the Display
Fn+F7
Mode" in the online document Customizing Your V AIO
information.
Switch to an Fn+F7
external
display
Toggles between the LCD, the external display
connected to the Monitor connector, or both
the LCD and external display.
®
Notebook for more