There are ice cubes in the bin, but no sound or action from dispenser. How do I tell if I need a whole new assembly or just the auger motor or just a new dispenser switch?
That is most likely to be the dispenser switch 6600JB3001C behind the ice paddle or the dispenser board EBR76249301. The dispenser switch is still available and can be tested fairly easily for continuity when open and closed, you can find how to access it by following the link attached below and referencing the video on that page or the video under the ice dispenser button ABH74219702. Unfortunately, the dispenser board and the dispenser assembly it came with have been discontinued by the manufacturer and are no longer available for purchase. The manufacturer does not list a compatible substitute or replacement part.
https://www.appliancepartspros.com/lg-switch-micro-6600jb3001c-ap4441530.html
https://www.appliancepartspros.com/lg-button-assembly-abh74219702-ap5673937.html