When the Revolution fixture is powered on, the front lens should move towards the front of the fixture. If the lens is already at the front, the end-of-travel sensor is detected and the lens will move to the rear of the fixture.
If the lens is not near the end of travel sensor and its first movement is towards the rear of the fixture, the system is detecting a false end of travel. The false end of travel signal will cause the fixture to drive the front lens towards the rear of the fixture to the point where it has hit the physical stop, at which point the belt will start slipping and make an awful racket.
Verify the end-of-travel sensor wire harness for the front lens is intact, and is properly routed. It should go under the Scroller hoop bracket, along the bottom of the fixture chassis, behind the post and under the Secondary Control Card (SCC) tray before combining up to the tray. If this harness gets pinched in between the post and the SCC tray, it can sever the wire and cause the failure. It is a three wire Red/Green/Black harness.
If the harness is intact, you will need to replace the End-of-Travel sensor.