Declaring he has "grave doubts" about the victim's testimony, a Los Angeles Municipal Court judge imposed probation and a $500 fine on a male nurse convicted in 1983 of sexually assaulting a male quadriplegic hospital patient. Turning aside a deputy city attorney's plea for a 270-day jail sentence for registered nurse Richard Lee Jensen, 41, Judge Richard C. Hubbell said he is "terribly concerned" about marital problems that Jensen has suffered since his conviction. Despite a probation officer's assertion that Jensen had once been accused of, but not formally charged with, sexually molesting a 6-year-old boy, the judge characterized Jensen as "a man of unblemished character and record."