Excellent fact finding and articulation of the various possibilities. With my experience in electronics I might suspect a bad ground to the motor or a motor that has failed (probably on the ground). But that would be based on what you have found to be apparently good and not with my experience with my AR8 (yet) one other question that you didn’t mention was how long you have had/used the machine. Obviously you know what you are doing and have been using the machine but sometimes any and all electronics can have an “infant mortality” where it will work great and a day or two later may fail due to a bad internal component that was good when tested and shipped but failed much earlier than normal use would have caused. I had my machine for 2 years before I ever set it up and everything ran fine but a couple days after I started using it, the Y axis stopped working. Turned out to be a bad stepper motor driver module… that just quit working. I’m sure none of the components on the machine go through a rigorous burn in. If they are all connected and operate properly when tested, they pass, and get shipped. (Which is normal and proper for normal equipment…. Different for military “mil-spec” electronics that is tested for hours or days at max temp, then min. temp to try to weed out “infant mortality”)
I would probably, at this point, call Axiom tech support (which is excellent btw) and with what you have and maybe check another couple of items, will have you diagnosed and on the way to a solution. Someone else may have more experience and be able to help…there ARE some crackerjack users with a ton of experience that may have run into similar symptoms.
Roger eaglecarver4.com Axiom AR8 Pro V5 Vectric VCarve 10.5 12 year w/ Shark HD (original version)