Take off blade guard, take off blade (left hand thread) unscrew two screws holding gearcase (gearcase is round shaft at centre, lift out secondary gear, there is a very small keyway at gear centre,(replace it ?) this is probably loose or sheared , mine appeared to be loose so I tapped it back in with a small jewellers screwdriver, shaft was now keyed to gear and I superglued the small gap where key was tapped in and it now works!
Phil Ward, November 2011