DIAGNOSIS Insulation on motor windings or wiring is overheating and burning. This is a serious fault.
FIX Unplug the blender immediately. Do not use it again. The motor or logic board has likely failed. This is not a user-serviceable repair. Contact Blendtec support or a certified service center.
IF THAT DIDN'T WORK Not applicable. A burning smell means stop use. There is no alternative user fix.
HEADS UP Continuing to use a blender emitting a burning smell poses a fire hazard and risk of electrical shock.