The voodoo of SCSI...

Ok, here's a nice one... I've got a SCSI drive that was working fine in a test system the other day. I came to plug it in to a system today via a known-working external SCSI box, and when I hit the power the drive didn't spin up and sat there with the LED constantly on. "Uh oh" I thought. So I turned off the power, unplugged the drive cable, and turned power on again - the drive span up fine. That's a bit worrying, I figure, so I plug the drive cable back in, but unplug it at the system end: I figure some fault with the system's SCSI bus is upsetting the drive. Turn on the power to the cabinet and... constant LED, no drive fault. Must be the cabinet's terminator, right? Wrong - with the power applied and the cable plugged in, but no terminator, I still get the constant LED and no spin-up. With just power applied and no terminator or cable, the drive spins up fine. So... that's just a cable fault left - must be a short between a couple of pins (however unlikely this seems). Wrong again - try a different known-good cable, and the behaviour's the same: no spin up with a cable plugged in. After a bit of experimenting, the drive will spin up fine with either no cable or a cable of a few inches plugged into it. With a cable of a foot (or more), it refuses to spin up and just sits there with the LED on permanently. Remember there's nothing funky at the other end of these cables - they're just stock 50-way IDC cable with 50-pin IDC connectors at either end. The fault is consistently reproducible - drive orientation makes no difference, power to the drive is good, cable-waggling has no effect. If I turn on power with a cable plugged in, *then* unplug it, the drive will suddenly spin up. So... huh!? It's as though something's gone bad on the drive and it's using the SCSI cable like and antenna and picking up interference which is confusing the heck out of it. But then why it does the same when it *does* have something at the other end of the cable, I don't know.