I just got done "repairing" an unreliable 4865, and thought I would post here in the off chance this helps someone else in the future.

I bought the drive on ebay as "untested". I used to think this really meant "tested, didn't work, want to sell it" - but after buying a lot of retro hardware and having most of it work I wasn't incredibly surprised when the drive arrived and read the first disk I tossed in it. "Untested" really does mean they don't know a lot of the time.

After a day or so the drive became unreliable, sometimes reading, sometimes not. After a week, it became physically difficult to insert a disk. I had to manipulate the disk by pushing upwards and then downwards. From this point on it stopped reading entirely with Not Ready errors.

After disassembling the drive I found that the head was visibly not contacting the disk. Pressing the head down lightly would result in the drive being able to read the disk.

There was a small padded square in the corner, over the screw - which for all the world looked like it belonged there. I figured it had puffed up or come slightly out of place, but after some testing found it was just loosely floating. I think it was originally glued to near the front of the drive - if anyone can confirm that I would love to know.

If you have a drive you cannot insert a disk into, or if the head is being pressed up and away from the disk, this might be one thing to check for.

A picture of the piece and a video of the non-contacting head are attached. Unfortunately my pictures of the piece where it was floating at did not turn out and I didn't notice.