Floppy drives commonly fail in DSS-1, see link above. NOTE these are double sided double density drives. If you don't use the right kinds of disk, they won't work also. Attain software above to create disk images on unformatted DSDD diskettes. I tried to troubleshoot one with some bad signal distortion from the digital domain. Gave up and got one to swap boards out of with a bad floppy on ebay for 50 bucks or so. Amazing bang/buck machines these days!
Parts:
The DSS-1 machines have a large number of chips since the things being done were still fairly new. But basically you have a computer running a sampling interface, 256Kwords of RAM for data and filters when the signal reaches the analog domain and a digital delay of course. Very challenging machines to low level troubleshoot in the digital domain. And really attainable at too low of a cost to spend much time going beyond this I think. :-) The DSM-1 is also inexpensive now but uses a better HD diskette drive but lacks the digital delay and no resonance control on filters, though they put 16 of them. However you cannot mix two sources/voice as you could on DSS-1. Thus to truly get the same sound it can be difficult to impossible if delay is used or resonance.
I have a scrap unit and odds are any of the parts are probably good. Let me know if you need anything!