Doing a channel scan using a set top box is useless and a waste of time. Channel scan are for when using the antenna.
Comcast requires the tv in cable mode if using coax or on an hdmi source when connected via hdmi. The TV must also be on channel 3 or 4.
If you are using a Comcast expansion box (2nd digital) and not the main box you will not get anything if the two boxes are not within range of each other or on the same cable system.
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