Okay you TV is hooked to a comcast modem? or do you mean My tv is hooked to the comcast converter box? A no picture but sound you want to first check you cables also try hooking up a dvd to the tv and see if that picture comes on if not and you got no pic and sound this would mean the backlight on this tv is dead or you got a bad inverter not converter, inverter inside the tv. Meaning it needs the repairshop but try and hook up a dvd to it and see if you got picture if so you cable box might be the issue call comcast!
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