OSI C4P MF floppy drive - troubleshooting

In addition to Mr. Willig's C1P (thanks!), I now have a C4P MF with which I am having floppy troubles. When I was a kid, I couldn't afford disk drives, so I'm not entirely sure what to do. - The machine works with a known good drive (an MPI from the C1P MF). However, it does not work with either of its own two drives. - All the power supplies are good--they all work with the known good C1P MF's drive. - When I answer "D" to "H/D/M?", the drive starts to step, then just stops. This happens with either drive (strapped to DS0), and with either just one or both drives connected. Are there some obvious things that I should try? I know I'm going to come off as a Philistine to some here, but are there any modern drives I can use (e.g. 360K double sided drives)? Does anyone know the secrets of the drive jumpers? (The C4P MF's drives have no indication of manufacturer anywhere visible.) I appreciate any help or advice you can share--thanks! --Michael Passer