you might want to get a new PSR 730 - has all features of the 640 ( floppy drive, etc, and then some) at cheaper price. THe PSR-640 had some fundamental problems with power supply for the FFD, and some updated major EPOMs that neede to be changed out. Those problems are fixed with new models. I think you can find the PSR-730 at about $500. Check
www.musiciansfriend.com.