Feel free to check out my site HERE for information about how to replace the belt in your FDS. If you have any questions, or can't get it to work right, feel free to contact me through my site or PM me here.
EDIT: The AC adapter for the Twin Famicom is DC 7.6V, 1.25A, center positive polarity. Any comparable AC adapter would work fine. A replacement AC adapter can supply a higher voltage and amperage, provided it's within tolerance of the internal 7805 voltage regulator. So, for instance, a 10V DC, 1500mA (1.5A), center positive adapter would be fine.