I have this DISK II drive labelled Drive B about 20 years.
I got it in a lot including an Apple II Plus with a ICE Cube Hard Drive, an Apple Cold Boot Adapter Card, a Disk II controller card and two DISK II floppy drives labeled Drive A and Drive B and a Z80 card.
Drive A is completely normal, I was able to verify that it was working perfectly.
I have never used Drive B because it has special features :
On its front face, next to the “in use” serigraphy there is an adjustable potentiometer which is connected inside the device to a prototype PCB board and it is also connected to the
analog controller board of the DISK II on Pins 1 and 11.
On the pictures, you can also see a 2-position switch which could make think of a 13/16 sectors switch but also an optical Red LED with visibly a mounting of an LDR cell below,
which would make it a hole detection 5-1 / 4-inch floppy disks (those used on single-sided 180KB PC floppy disks).
So here is a very particular setup that leaves me quite perplexed as to the use that has been made of this very particular floppy drive.
Have some of you ever seen this kind of modification on a Drive Disk II?
In advance, thank you for your answers.
Best regards from France.