Sony WEGA KV 36FS13 Operating Instructions Manual page 27

Installing the TV
To use PIP with the Cable Box
Turn on the cable box and VCR. Use the remote control's TV/VIDEO
(yellow) button to set the PIP output to VIDEO 1. Change the PIP
channel via the cable box. (The cable box's tuner is used as the
PIP video source; if you do not turn on the cable box, the PIP will
not work.)
This system is needed because the cable box unscrambles only one channel at
a time (unlike regular cable, which makes all channels available concurrently).
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