how can i fix magimix 4200?

i can only answer for the old 5400 magimix it had centre peice at the top of the blade in the shape of a cone which ended in a rounded metal point when the lid was placed apon the dicing chamber it came in contact with the rounded metal point this would stop the blade from lifting. the part i discribe was seperate from the blade it just fitted in some slots at the top of the blade

Bruce
May 2013