NEC LT260 - Manual (Page 41)

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Press and hold the SOURCE button for a minimum of 2 seconds, 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