I am Peter.
For this build, I am using AR2.0 s/w with Aluminum kit.
Working through the build, the J3 motor doesn't seem to move the arm much. The arm remains in the position of touching the J3 limit switch.
I even tried connecting J3 motor to the J2 motor wiring to see if I was able to "jog" J3 via J2 + - buttons but it had the same result - not much movement.
NOTE: With the system off, I am able to easily move the arm up and down. So, I can confirm that the arm joint is not stuck.
Any suggestions on the cause and fix?