Its not uncommon for D800(if memory serves-a diode near the back scsi port) to fail and you get no power to termination,hence it doesn't work. You can check it with a multimeter for 5v on both sides with the machine powered(it may read 4.8v+ which is ok).
some diodes were installed backward from the factory causing random scsi issues..
Good idea to update to a WD rev8 scsi chip or AMD 33c93A,it solves some multiple drive scsi issues the old chips had and are cheap.
on the A3000 its sockets sockets sockets! Stop and reseat all the chips,these old sockets are notorious for bad contact especially after the machines been in storage. Doing this prevents you chasing your tail and random problems.
Check the power supply for +5,+12,-5v etc.. These old power supplies can need recapping. Low voltage will cause a host of odd problems.
I suggest you buy a buster 11,they are still available and its a good upgrade.
