:-? For the SCSI trouble, I assume that we've checked the obvious things like termination at both ends, a unique ID on each device, and so on? Often it's the simpler things that will get you.
;-) As for the jumpers on your SCSI controller, you might want to check
this site. They legally host archives of drivers for obsolete Amiga hardware. The install disks and documentation for your SCSI controller may be there.
