Your TV should have nothing to do with recording shows on cable TV if you've got everything connected correctly.
If you don't have a cable box, connect the incoming cable coax to the Mag's ANT IN, then coax out from the Mag's ANT OUT to your TV's ANT connection. Then, a separate connection from one of the Mag's outputs (HDMI, Component RGB, S-Video+WR audio, or YWR RCA) to your TV. If using HDMI, you must press the HDMI button on the remote to activate the HDMI circuit for 1st time use... it has four HDMI formats you can choose by pressing multiple times.
Then, of course, you have to do a channel scan in the Mag... Auto Channel Preset > Cable (Analog/Digital) in your case so the Mag can find all available unscrambled cable channels for tuning and recording
The Mag's in/out coax circuit is a built-in amplified splitter that feeds the tuner on one path and downstream components (TV or cable box) on the other path.
You'll only see the raw signal thru the coax to the TV where the TV can tune any channel it wants. The Mag can then tune and record any other unscrambled channel independently, so you can record one channel while watching a diff. channel with the TV's tuner.
If you have a cable box, it's a little more complicated, as shown in Sketch 3 here. Only if recording SCRAMBLED (encrypted) channels from a cable box does the CABLE BOX (not the TV) have to be on the scrambled channel you want to record (since the Mag can't descramble encrypted cable channels).
Click the 1st link in my signature for a list of other info and help files.
|Magnavox Mdr515h 500gb Hdd And Dvd R With Digital Tuner|