I have wire EDM with fanuc 6M control,
with yellow cap DC servo motors and Velocity Control Unit H201
Its Y axis is running fine,
but if I move X axis in -x direction, it gives alarm 401,
in +x direction when I inch very slowly it moves, but when it is moved bit faster it gives 401 again,
In the Velocity Control Unit red TGLS led lits up.
The DC motors of both axis are identical so
I swapped the motors of X & Y axis but the problem nothing changes.
If you swapped motors and the problem stayed with X axis then the problem has to be in the cables or the servo amp. Can you rotate both ball screws freely by hand? Does your EDM use linear scales for feedback?
Yes ball screws are free, in fact I have disengaged motors from ball screws,
and my EDM do not have linear scales but there is one Inductosyn/Resolver unit
is there which is attached to master PCB and feedback from motor goes to this card.