Meanwhile my SY-85 saga continues. First I ordered a replacement floppy drive and adapter; the adapter didn't fit, so I ordered a second one for £35, specifically for the SY-85. This fitted and the drive works. Then I ordered a USB floppy drive for the PC, but this wouldn't read the blank DD (720kb) discs which the SY-85 (old drive) used... so I ordered some HD discs, thinking that these should work with the new drive. The new discs work with the USB drive (yay!), but don't work with the SY-85! So I have a HD-only PC and a DD-only synth.
Now I have to find a DD USB drive - which is not easy.