The Service Manual covering mixers with the control plate can be downloaded at:
Things to consider:
The brushes have a chamfer on one edge and must be oriented so that the chamfer can pass a small stop in one corner of the brush sleeve.
Are all the wires to the control board connected correctly? The board is marked for the wires colors.
There are instructions in the manual for measuring the stator coils to find out if they are OK or not.
Checking out the armature is another whole thing and you can get information on-line about this (try searching "armature testing"). I really hope that you don't need to go this far.