Diagnosis Murder

"Matlock" (ABC), "Murder, She Wrote" (CBS) and "Diagnosis Murder" (CBS): What do they all have in common? Writers who don't have to resort to sex and violence every week to put on a good program. Catherine Lee, Culver City

"Diagnosis Murder" is for Dick Van Dyke fans who will accept him in anything, no matter how inept. Premiering at 8 tonight on CBS (Channels 2 and 8), the "lighthearted mystery" series stars Van Dyke as physician Mark Sloan, a teacher and chief of internal medicine at a large hospital, positions that naturally allow him to spend chunks of his day investigating homicides.