Retrofitting a 1986 Maho MH 700c

Do you have the schematics for the drives?
-
This is just thoughts on how i would go about checking this, might be OK now that i had some time to analyze the symptoms :
-first check the power going to EXE boxes, is it the same voltage on all 3 or 4 of them?
-is the power for the EXE coming from the Indramat drives?
-if yes, are they all powered from the same rail or do each have it's own power regulator?
Assumption: given the info i would check the Indramat drive for rust on the EXE power rail, it is just to convenient given X is fine, Y faults at the end (meaning a bit lower voltage so accumulating PID error), and Z faults immediately, this also assumes the voltage regulator to be near the X axis drive/feedback and furthest from Z axis drive/feedback
-All of the above is valid if drives/motors use tachos, so same checks on the tacho feedback voltage regulators.
-
Stopping here for now, to much assumptions and unknowns that need confirmation or denial!