The KitchenAid KSM 90 WW stopped working. The motor runs normally, at least it seems to. However, mixing mechanism does not turn and the attachment mechanism does not turn. And I do not know how to get into it to see if a gear slipped off or something. I need a manual or schematic with a explosion view.

SOURCE: bread dough hook slips when mixing

This is not a solution but I think you have a serious problem you might have sheared some gear teeth whent the mixer jammed and it only manifests itself under a heavy load, I would take it to a repair guy, those mixers are expensive and it would be worth it.

SOURCE: seating the brushes on the Kitchenaid ksm90 mixer

You don't need to seat the brushes. Remove the brush caps and pull the brushes out by their springs, being VERY careful to note the position of them since they only go back in one way. Measure the free length of the spring before pulling it out. It is critical that you write down the length sticking out with very slight pressure on it so that it is seated against the armature when you measure.

Clean the curved surface of the carbon brushes with a sharp knife being careful not to scratch the curved surface. If you have them installed wrong they will not go all the way in and will not contact the armature and it will not run. Measure the length, as done above, of the spring to make sure it is in correctly!! If it is not in correctly the spring will stick out 1/4 inch longer than it should.