I had something similar happen on a 15-91 with the potted motor. The machine seized up on me though the motor worked properly once disengaged. I reoiled or retriflowed and examined the entire machine for obstructions. No obstructions found, I removed the handwheel to get a piece of leather and vise grips on the shaft. I then carefully rocked the shaft back forth to unseize which worked. Too much pressure on the vise grips and a part could break. I believe my problem came from a seized part under the faceplate. Good Luck
Jon