(Off topic, but you seem interested. I'll post this one and then stop unless there's a lot of engagement.)
I have a diagnosis on the Osborne. It has two full-height 5.25" floppy drives ("Mommy, what's a hard drive...?") -- this particular example has one each of the two that Osborne used, Siemens and MPI. The MPI one (a Model 51) has a defective spindle motor... it spins by hand, but not by electricity, so I suspect the windings have shorted out inside. As luck would have it, eBay has exactly one full-height floppy drive, and it's the exact make and model of the deceased one I have! I'll have to save up a little and hope it doesn't get bought out from under me... but I might be able to get it. Time will tell.