When turned on, the mixer hesitates for a couple of revolutions and then does nothing.
If the motor is continuing to run then you will want to check the worm gear for and gears that meet up to the worm gear for damage. Also check to make sure that the planetary is not dropping. If the motor stops running then the phase board would most likely be the cause for the issue.
What causes it not to start up and it smells like electricity burning?
The first thing that you will want to check would be the brushes to make sure that they are in good shape with no burn marks from arching. There is a screw on the side that you would take out and this is where the brushed are located. If the brush looks ok then you will want to check the governor and the phase control board for being faulty.