Early 1980s, after the Top40/CHR audience had migrated to FM, particularly the original KHFI 98.3.
The format only lasted a few years, fizzling out as the music audience for AM vanished. The KNOW call was dropped in the late 80s, going through several changes and formats up to the current Sun Radio KTSN.
IIRC the KNOW call popped up on a Longview station for a few years before winding up on Public Radio FM in Minneapolis/St. Paul in the early 90s, where it remains today.
The original 102.3 in Austin, KMXX, had Spanish language programming from 5am to 9pm, and African-American target programming 9pm-1am. That would have been around 1976.
KAZI 88.7, which launched in 1982, had a strong African-American lean which somewhat filled the UAC genre on FM.