The drive belt inside my Sakhr FD720 is broken. The floppy drive in the FD720 is Mitsumi D357B. I did not find a belt for this drive, but found a belt for Mitsumi D3578. I ordered the belt thinking the D357B and D3578 drives are the same (B is usually mistyped as 8). It turned out the D3578 belt is 5mm wide while the D357B's is 3mm only. The belt dimeter for both drives is the same, 120-125mm.
Instead of retuning the 5mm belt I received, I decided to cut 2mm out of it! I put a masking tape covering 3mm of the bell's width and cut the excess 2mm using scissors. It worked and the drive is operating normally now.
