The Okidata 3305 is a 1/3 height 5 1/4" double sided floppy disk drive.
Unlike other floppy drives, it uses an Intel 8742 microcontroller to control the head stepper motor and presumably other functions. This is ridiculous overkill, floppy electronics is quite simple and Okidata could have used a handful of TTL to do the same job.
(In the picture, you will notice that the 8742 has been removed. I have people at work who are really good at that).
I have two of these drives, and they have been stored in an attic. Nice and warm. Bitrot inducing warm. So the motor comes on, but the heads don't seek. I pulled (as mentioned above) the 8742 and dumped it, 0xFF all around. Maybe I can write some code to recover the data. Maybe start here.
This Okidata 3505 (from an eBay offer) shows that they later redesigned the PCB (the rest of the 3505 is very similar to the 3305) to eliminate the 8742.
|DS 0||Drive Select 0|
|DS 1||Drive Select 1|
|DS 2||Drive Select 2|
|DS 3||Drive Select 3|
|MX||Drive Selected by the Drive Select signal|
|HS||Head Load controlled by the Drive Select signal|
|HM||Head Load controlled by the Motor On signal|
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