Thanks for your thoughts on diagnosing it. I was almost certain that the remaining problem had to do with the board, not the motors, etc. I remember taking apart a 10 MB HD to see the damage inside, and figured if it came to that with this box then I'd have no hope.
I did some more searching using "Seagate 7200.8" and found forum.hddguru.com . It has lots of good information about fixing drives.
The contraption that got roasted on the original circuit board of drive is a "TVS" - Trans Voltage Suppressor. It's a diode that's designed to protect the rest of the electronics if bad things happen to the input voltage. It's apparently quite common for them to fail via a dead short (as seemed to happen in my case based on the PS issues I was having).
http://forum.hddguru...t9998.html#p70888
So I had an excuse to drag out my soldering iron. And guess what? Removing the roasted TVS fixes the drive! Woot! :-D
So, I'm out $50 for that replacement circuit board (which I'm under the impression should have worked), but I've apparently got all my old data back. But, while replacement TVS parts apparently are available, I think I'll play it safe and relegate this drive to the parts bin after I get all the data off it.
Thanks.
Cheers,
Scott.
(Who has turned it off until he can get another drive ready to back it up. And who is much more careful about hooking up power connectors on open PCs now...)