NEC LT240K - Manual (Page 40)

E-40
Press and hold the SOURCE button for a minimum of ONE second,
the projector will search for the next available input source. Each time
you press and hold the SOURCE button, the input source will change
as follows:
→ RGB1 → RGB2 → Video → S-Video → Viewer 
If no input signal is present, the input will be skipped. When the input
source you wish to project is displayed, release the button.
Press the ENTER button.
PROJECTING AN IMAGE
Ͼ
Selecting a Source
Detecting the Signal Automatically