While noodling around on YouTube, I've been seeing a lot of comments on Amiga-related videos where people say that they had an external diskette drive for their Amiga computer but the drive stopped working properly.
This may not actually be the diskette drive. So before you throw the drive in the trash or recycle it or commit it to some other horrible fate, try testing the drive on an Amiga that has no issues using a different external drive (contact a friend who has a working multi-diskette configuration and see if they'll let you test the drive).
It could be that one (or both) of the CIA chips in the Amiga are fried.
Possible causes include unplugging and plugging parallel, serial, or disk drive cables while the Amiga is on.
You can unplug and plug parallel and serial cables on a powered IBM PC. However, on an Amiga you can damage your machine doing that. In the past I repaired a number of OCS Amigas with this condition.
This also means that some of the diskettes out there that are supposedly bad, aren't. Again, it's worth testing on an known good machine.