Failed 5.25" Disk Drives

["Terry Olsen" <tolsen64@hotmail.com>]

I had a guy come over to my house to buy a 5.25" disk drive because his
weren't working.  Scenario went something like this...

1. He brought his IIe system & disk drives.  Hooked it up, turned it on.
Drives light up, spin, but don't boot or read.  No head movement or standard
"machine gun" booting sound.  Tried both his drives daisy-chained, reverse
daisy-chained, and each individually.

2. Hooked one of my drives up by itself. Booted fine, read/write fine.

3. Wanted to try his drives.  Daisy-chained one of his drives off of mine,
turned computer on, nothing.  My drive now acting like his.  Unhooked his
drive, tried mine alone and it is now toast.

4. Grabbed another drive from my stock, hooked it up by itself, works fine.
Daisy-chained my newly "toasted" drive and tried it again, toasted another
drive. Now I have 2 bad drives.

5. Grabbed 2 more drives from my stock, plugged them in, they work fine.
Sold him the two working drives (didn't charge him for the drives we toasted
while troubleshooting).  Told him to mark them as bad so he wouldn't hook
them up.  Sent him home

Now...I have 2 toasted drives.  What in the world can blow a drive up in
such a way that the newly toasted drive will become the bomb that toasts
other drives?  What do I do with the drives now?  Can they be fixed?  Do I
throw them away?  Any advice?

Thanks!
Terry