Traduzione in corso passo 1
Remove the hopper and take the upper burrs out. Empty out any coffee grounds (An air gun or vacuum helps) and then inspect the impeller blades.
If the impeller can fit through the hole (ie: be removed just by taking out the lower burr) then it definitely needs replacement.
A good impeller should not be removable without dis-assembly and the tips of the impeller blades should not be visible.