I don't know what kind of psu you're using to power the a590, but the original psu is not strong enough to power modern drives. I've bought 6 scsi drives recently like you, and four of them had symptoms like yours. I got suspicious and connected to my pc and voila ! all of them spin and work flawlessly with the pc supply. I recommend you try them on your pc (the first two) before you throw them away.
