DIAGNOSIS You're likely overheating the motor. That smell is the thermal protection system kicking in. The 5200 has a powerful motor, but it's air-cooled and needs breaks when working hard. Running it for more than 5-7 minutes continuously on high with a very thick mixture (like nut butter) will do this.
FIX 1) Stop using it immediately and let it cool down completely for at least 30-45 minutes. 2) For future heavy-duty tasks, use the "pulse" function or alternate between high speed and low speed. Never run it on high for more than 5 minutes straight. 3) Make sure the base vents on the bottom aren't blocked by a towel or sitting on a soft surface.
IF THAT DIDN'T WORK If the smell happens quickly even with a thin mixture (like a smoothie), there could be a fault in the motor or its cooling fan. Listen closely near the base vents for the sound of a small fan whirring when it's on. No fan sound means it's not cooling itself and needs professional service.
HEADS UP That thermal cut-off is a safety feature. If you ignore the smell and keep pushing it, the blender will eventually shut itself off automatically to prevent damage. Letting it cool is the only way to reset it.