Robotic maintenance was considered for SAGE in the 1950s. Robots were never built for that, but the SAGE racks were designed with easy-to-handle plug-in rack modules with all connections on the back.
(Vacuum tube failure wasn't a major operational problem with vacuum tube computers. For the UNIVAC I, normal procedure was to power up the machine and set it to 10% overvoltage mode for 10 minutes. This would burn out any tubes near failure. Those were replaced, and the machine would then run for the rest of the day without another tube problem. Since the machine had a dual CPU for self-checking, any problem would cause an immediate stop.)