This is about a KM070 a.k.a.Cooking Chef but it's probably similar for other models. The images and words are for grown ups. If you end up cut or electrocuted you're not really grown up enough.
If your Kenwood sounds like this
then the gearbox is up the chuff.
Take it apart and remove the drive assembly. The hard bit is how to remove the large drive belt sprocket.
Credit to http://www.thebigchef.nl/kenwood-a901-opknappen/ advising that you lock the low speed outlet with a mincer attachment and turn the wheel anti-clockwise
Credit to me for how to lock the mincer
Jam a piece of steel between the screen and the blade, I used a short hexagon key
Don't worry, it bears on the trailing edge of the cutter
Everything looks ok here
so undo the nut in the middle of the planetary thing from underneath
Oops, chewed teeth
and silvery bits where there shouldn't be any
Inspect the mating gear, mine was fine
Clean this lot up and order the spares:
- gearbox lower cover assembly
- grease
- silicone sealant