I stubled across this document via the Synthzone archive of the "Roland Arrangers Group" data: http://web.archive.org/web/20040627121722/http://www.daytonamusic.com/rag/faq.htm#Disk%20operations

It states:

Q: Can't I substitute a regular PC floppy drive for the keyboard's drive?

A: Not likely. Roland employs an "enhanced" floppy drive (Chinon FZ-357) in their arrangers, capable of doing things like signaling a disk insertion to the keyboard and continually spinning even when not being accessed. Although the drive connections appear identical to the PC's, there seems to be different wirings and additional signals used by the keyboard. Anyhow, if you can purchase a drive from a Chinon rep (about $150) it will still be a lot cheaper than going directly to Roland (up to $300 as reported in the group).

I've just done a quick Google for Chinon FZ-357. And ... it seems you can use these to fix Ensoniq Mirages; the alternative fix being a Teac! This document http://www.flippers.com/TEAC_FD235_jumper_pins.htm gives both sets of settings and so might help in setting up the Teac by cross-comparison.