Just wondering how important is that curcuit .
And the best way to find the fault itself.
Glad you found the problem and got it working again.
The limit switch was an option, maybe it was used for a reason before you got the robot? they were mostly fitted to limit the base axis rotation.
I can only suggest you trace the wires from X1 2B & 3A, if you need more access it is possible to lay the robot on it's "back" on a wooden pallet for support (2 people can safely tip it over) then remove the thin metal plate that covers the base. If the wires go back into one of the plugs/sockets, give me the X terminal numbers and I should be able to tell you where it goes next.