Misterious problem with UniDisk 3.5 drives and disk controllers

[erolfi@gmail.com]

I'm seeking for help in a very strange situation with various Apple UniDisk 3.5" drives that I own.

I was trying to repair one of those external drives that came with a Macintosh Plus.
I removed the drive from its enclosure and installed it into an UniDisk3.5 case, removing the original drive from the UniDisk.
Then I connected the drive to an AppleIIGS, and started fiddling with the drive open (like an open-heart surgery) by moving the stop sensor while the Apple IIGS was running and sending PR#5 commands to test. Suddenly, as I slightly moved the grey flat cable that connects the drive to the UniDisk case internal controller, the Apple II kind of resetted itself (maybe the cable was defective and shortcircuited). However the drive kept acting normally after the accident occurred. So I kept trying to move the stop sensor and sending PR#5 on the AppleII and I made other tries to realign the heads stop sensor, and then the shortcircuit problem happened two more times (again with no consequences). But the last time that the shortcircuit happened again, the drive was not responding anymore. It turns on and moves the heads, but it does not spin (just spins for an half second sometimes when the disk is inserted), and when I type PR#5 on  the Apple II keyboard, the Apple replies "Device not connected".

Then I put back the original drive in the UniDisk case and - to my surprise - it was not working too. So I thought that maybe the controller inside the UniDisk case had broken.
However, being certain that the original drive from the UniDisk case was good, I installed it inside the Macintosh as an internal drive, and it was still not working!
So I concluded that maybe the two drives broke after the apparently shorted UniDisk controller.

Then I put back the original internal drive into the Macintosh (which I never connected to the broken UniDisk controller). And - pity - now it was not working too.

This is too bad because it seems to me that now I have all the drives broken, and also the Macintosh drive controller (on its logic board) seems to be broken.

Strangely, the Apple IIGS controller seems ok, because I connected a Liron on it and the Liron still behaves correctly.

I have a bit of knowledge in electronics but I really don't understand what could have happened, and how it is possible that this failure seems to spread like a virus on every controller which I connect the apparently broken drives to.

Besides, the apparently broken drives turn on and even realign the heads if you move them forward before turning them on, but they  seem to not communicate with the computer at all.
When I turn on the Mac, it shows no signs of trying to read the disk, or even less trying to eject it. And the Apple II says "device not connected".

I was wondering if you ever had such a problem with Unidisks/Controllers and if you would please have any suggestions as how to proceed. Thank you everyone.