Retsch DM 400 - Manual (Page 46)

Servicing
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9. The fill hopper (4) must be removed to dismantle the fixed grind-
ing disc (5).
10. To do this, manually close the grinding chamber and remove the
3 cylinder screws shown.
11. Remove hopper from the front.
 The mounting screws on the fixed grinding disc are then visi-
ble!