Additional :-
I've found the correct jumpers now, but i'm having trouble with images created with the hxc floppy emulator Software. Strangely enough, if i format the image that the SY calls 'bad disk' on the Yamaha SY itself, they format fine. Then i can save files to that formatted image all ok and even load the saved files back in perfectly.
I can load that new image into the hxc emulator software ok, delete the files and add new ones (720k PC disk format) and export; load it back into the SY and surprise surprise, bad disk error again.

Additional 2..
I found now that if i write the files to a real 720k floppy disk, then re-grab it using omniflop, then convert that image using the hxc software and export it to a .hfe file, it works fine. So what is going wrong with the normal create a dos disk and export in v2.1.6.0 software??
Chris