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If the blades stop moving but the motor keeps going then the clutch assembly that engages the blades could be worn out.If the blade and motor both stop working, then the motor may have faulted or the capacitor that helps provide motor with power when more power is needed may seen its days as well. I hope this helps answer your question, if not, it'll give you a starting point. I'll switch this to Q&A so if you have anymore questions, please ask. I wish you the best.