PHILADELPHIA -- Imprisoned actor Bill Cosby is renewing attacks on a Pennsylvania trial judge as he again seeks bail while he appeals his sex-assault conviction.

Lawyers for the 81-year-old Cosby filed a bail motion Wednesday with the state Superior Court. They complain that Montgomery County Judge Steven O'Neill has not issued a post-trial opinion explaining key trial decisions in the seven months since Cosby's sentencing.

The defence needs the opinion to pursue Cosby's appeals. There is no deadline for judges to file their opinions, and some spend months on them in complex cases.

The motion accuses O'Neill of harbouring a personal grudge against a defence witness. O'Neill's office says he won't have a comment on the motion.

Cosby is serving a three- to 10-year prison term for drugging and molesting a woman in 2004.