A system for selectively disallowing unwinding of a storage library robotic mechanism cable assembly in a direction that would otherwise allow a platform of the robotic mechanism to move downwardly via the force of gravity while at the same time allowing for winding up of the cable assembly and the platform, such as during shipping, manual access, replacement of the robotic mechanism, and/or the like. The system may include a ratchet pawl for engaging between adjacent teeth of a drive assembly of the robotic mechanism and an actuator for selectively moving or allowing for movement of the ratchet pawl into and out of the engaged position. In one embodiment, the system may include an electric switch or the like to sense when the pawl is engaged with the drive assembly.