I've never worked on a Miprom 21 that you had to do anything like that, unless its a permanent magnet motor that needs an encoder alignment. I have worked on a couple with HPV900 drives and if I remember correctly, it was setup more like an analog DC drive i.e. all discreet between MSU & drive so you wouldn't have access to the drive menu on the service tool. You probably had a bad MSU card, all the pattern manipulation happens there except when NTS clamps. replacing the CPU is no big deal, just move over the PROM board, do a HW scan & touch up floor heights.
