I just got a used SY99 with a defective disk drive. When a disk is put in the drive and any disk mode option is selected the red light goes on and the Synth locks up. Is this problem fixable? Can I fix it or should I take it to the dealer? Do I need to replace the drive? Please help me out here.

I don't have a sy99 but this sounds exactly like the problem that I and many other sy77 users have had. The problem is with a rubber belt that turns the drive reader. The belt gets worn out and too slick to turn the drive and just starts slipping. I found a replacement belt at an electronics store and replaced it myself. Now it works perfectly.

Are these standard DOS 3.5 Floppy Disk drives? I have a few 3.5 floppy drives in boxes that I don't use so I probably will have to disassemble the SY99 to figure out the fix-weather it is the belt, or the drive. Too bad you can't just pop a new drive in there. A standard Floppy Drive is only about $20.00. I'm sure an OEM drive, if available, would be like $50-100.00.

It is not standard. I took the whole drive into the computer store and they looked at me like "what the hell is THAT thing?"

So I took it apart and discovered the belt problem. Cost me less than $10 to fix it. Here is the link where I am describing the process to Snoids, another victim of the disk drive belt.
http://www.synthworld.com/ubbs/Forum26/HTML/000573.html

Thanks for the Info and the link. I will follow your procedure as much as I can. I am hoping that my SY99 disk drive is the same as your SY77's. I think once I figure out what size belt I need I will go back and get 2 or 3 more of them to have on hand.