You'll need proper termination. Terminators must always be two, at the end of the cable. Vintage SCSI devices have termination option built-in, so you'll need to activate termination on both the adapter and the drive. Older devices have two or three resistor arrays/packs labeled 220/330 or 221/331 (passive termination), slightly more modern terminators are active and activated by setting a jumper. If you've got the choice enable 'term power' on the adapter and/or on the drive as well.
