Hi, the 5790 was either the FLEX XP or the CONTOUR series. In my experience as a Braun Service Dealer the tightening of the head is not your problem. If you have excessive vibration I believe the inner frame has cracked or broken. Really this repair should be done by a Braun dealer although not impossible to do at home. You will need the correct replacement spares and the correct drivers to get inside. If you want to talk further my number is below. Thanks Jason @ BRAUN SERVICE
JASON @ BRAUN SERVICE 01273 734424, February 2009
