This article is from the RCA SelectaVision VideoDisc FAQ, by email@example.com (Tom Howe) with numerous contributions by others.
Although at first glance identical, minor cosmetic changes were made
with the K series on the front panel, buttons, and remote control. In
addition, some refinements were made to the circuit design, resulting in
some component value changes, additions, or removals. When servicing
these units, it's necessary to use the service manual specific to that
particular J or K series model.