Check the keys for the motor shaft, that is what ended up being wrong with the woodsman, it would run fine till you put something into feed. Then it would dead stop.
The brunt of my experience working on chippers is centered on replacing keys on the motor shaft. A few times we got the wrong size and had to file them down to fit but even the exact key was always a PITA to slip it in "just right". Lots of deadwood or pushing too big of trunk through always seemed to be the culprit. 'Twas a lesson hard learned.