Methods and apparatuses by which an oxidized metallic surface can be prepared for a subsequent repair operation without excessive removal of parent metal material. In one example, the lock aid includes a Schmitt trigger having an output, a switch having an output and an input coupled to the output of the Schmitt trigger, and a voltage controlled current source coupled with the output of the switch. A rotation control mechanism selectively restricts rotation of one of the first and second rotating elements of the planetary gear set to establish a fixed speed ratio mode, and releases the one of the first and second rotating elements to establish a variable speed ratio mode.