well you can always try what is suggested by little forker and put the brake unit on another machine and see if it works.
Or you can apply signal voltage to it and usually you can hear it clicking in (actuating) for releasing.

when you removed the cover did you notice anything about the standoff's where the power cables hook to it? they should be fixed in a solid position, not loose. If any of them are loose then the controller will have to he replaced.