I haven't had one of these focusers, but I did look at some video of them. I assume that the knobs turn freely but don't engage? (If so, do you see the small knob turning evenly/smoothly 10 times for every rotation of the larger knob? Sometimes two speed focusers can have problems with the relative adjustments of these that can cause grinding, lack of engagement between fine and coarse focus, and other problems.) I also assume you have tried adjusting the top tension knobs and the bottom tension knob without getting it to engage.
If all of the above seems okay, then I would check those hex screws on the bottom to make sure they are evenly tightened. If that does nothing, then t might be time to remove them and check the pinion gear below, to make sure it is seated properly. I also saw a link to a problem with several ES scopes that had loose screws in the drawtube racks themselves. That was allowing the rack to shift back and forth.