My Book with Cablevision SAv 8300Hd with cable card partial records

I purchased a WD My book 1 TB Av to use with a cablevision SA 8300 DVR with a card. It installed and shows an increase in storage spae but it does not always record the full programs. e.g. if a program is an hour I may get 15 minutes. This is consistent. This drive is supposed to be compatible with this box. I tried resetting numerous times, reformat, another drive and still get the same. I am at a loss and get no answers. what am I missing. What do I need to do to make this work. It formats and says averything works but I cannot record the full program.

Hi andrewj, I would try connecting the My Book AV to a PC and running a DLG test, if the test completes successfully contact the cablevision manufacturer or provider for support on how to make it work.