1) SysAxe drives should use the grey terminator, even on a IIfx (The IIfx came with a special black terminator).2) The SCSI ID should be 5 or lower (6 = Mezzo, 7 = SysAxe).3) Excessive SCSI cabling, or SCSI ID conflicts with multiple drives.4) Older firmware on Micropolis drives (models 1528 & 1598).5) SysAxe might need the current Xilinx chip @ U37 (see supp below).6) Drives may need to be reformatted (try Silverlining, leave the default settings for Mac Hardware Handshakes).7) Try mounting it on the Mac SCSI and install SCSI Driver with formatter.8) Quadra 650 might not provide enough space for a robust connection of the 50-pin cable that goes to the drive.Check the following socket locations for current revs (an ink dot means the PAL had been revised but not relabeled):U17 should be 200137-003. U19 should be 200134-003. U20 should be 200132-003. U37 should be 200 139 004 or BUSC B06. U22 should be 200140-001 or ROM v1.0. The Sys Axe may also require a "resister pack" mod that must be performed at GMR. You can identify this by examining the back of the card opposite U18 to see if a very small "surface mount" resistor has been soldered on.