Vintage Synth Repair

Hi Brofjw,

I'm not familiar with this machine, but I AM painfully familiar with the quirks of SCSI, from an IT point of view. SCSI Hard drives (HD) in your Kurzweil will actually be the same as the ones in computers, and the controllers will be the same as well.
I used large SCSI RAID arrays on huge servers for years. Mostly, it all goes fine until either a power-off, or a replacement disk.
It's usually down to clashing SCSI IDs. If you can set the SCSI IDs via hardware (usually DIP switches), DO IT. The software will usually defer to the hardware settings. (but not always)
I've had machines lock-up due to some numpty slotting in a new HD without changing the ID. 
It may be that your Ids were set by the software, and all was going well until you plugged-in that HD, with a clashing ID, which over-rode the software settings, and the software is now confused. You probably need to change the ID on the suspect HD (DIP switch?), and then somehow reset the software to read the IDs again.

Computers with SCSI tend to have a SCSI BIOS, stored in CMOS memory. It's possible that this has been corrupted, and needs refreshing ("flashing"). Go only knows how you's flash the SCSI BIOS on a Kurzweil..

SCSI - It's a minefield.

Best of luck! 
 
** Try setting the IDS via the dipswitches before you mess with anything else! **