An interesting Disk ][ Interface Card Fault 
tl;dr: I recently got into 8-bit Apple retrocomputing due to my work with Adafruit. I had a Disk II setup that couldn't write to any floppy. I fixed it by replacing a 74LS05 IC on the Disk II Interface Card.
An interesting finding about Apple DOS 3.3 diskettes 
Generate the 64 GCR values used by Apple DOS 3.3 and ProDos