"Bad disc" problem with a Sharp DVD-SV97

Hi There,

I bought the unit and play only store purchased original DVDs with that. I have quite some and the unit sometime starts to play the the but most of the time it says bad disc. Then I need to turn on and off 5-10 times and then it starts to play the disc. Sometimes it even freezes halfway with the playing, image gets still and then after stop/restart the bad disc nightmare comes. Other times it plays 3 discs without any problem (same ones). I even left it once for a full night and it was playing in the morning. My “test” discs are brand new, bought three movies yesterday. Is it a problem which is obvious to solve or just return the unit for repair?