Folks, I had an unfortunate clog event (after many successful prints)... After installing a new nozzle, reaming the Teflon tube, etc. I had no joy. my suspicions turned toward the extruder / filament feeder. To get a good look at what was going on, I unmounted the hot end, learned how to manually send codes for extrude and now am simply trying to feed filament into open air... What I see is that the motor seems stuck... That is, it stutters, the filament moves back and forth but never goes forward. Manually turning the motor shaft has the desired effect of pushing filament thru?