When I acquired my Apple IIe, Disk 2 was not reading at all. I found a blown transistor in the CA3146 chip. I replaced this and it was still often unreliable in reading. I've just looked at it again and swapped the analog boards, both boards function OK in Drive 1. I then noticed the silver tray clipped onto the frame was missing from Drive 2. Fitting the tray from Drive 1 fixed the problem.
It seems the tray is not just a dust shield but is a screen to shield electromagnetic inteference from the sensitive head.
I presume a previous owner opened the drive to fix the fault and forgot to put the tray back!
I now need a soup can and some tin snips.
It ain't pretty, the Heinz screen (other brands are available). But it works. If you are fixing a vintage Fender electric guitar, you don't use PVC wire, you must keep the original wiring. In computing, the first fix that works is used.
Original replacement parts are available from ebay for around $11 !
(Incidentally, I did notice that when the drive door is open the top of the spindle is very close to the component leads on the analog board, so I trimmed the component leads)
HeinzScreen.jpg
That tray is only there on later drives. Earlier drives did not have it. It isn't to shleld the head FROM RFI, it is to keep it from emitting RFI.