Reading Floppies With An Oscilloscope

There’s a lot of data on magnetic media that will soon be lost forever, as floppies weren’t really made to sit in attics and basements for decades and still work. [Chris Evans] and [Phil Pemberton] needed to read some disks that reportedly contained source code for several BBC Micro games, including Repton 3. They turned to Greaseweazle, an interface board that can dump just about any kind of floppy disk if it is attached to the right drive. The problem is that Greaseweazle couldn’t read the disks due to CRC errors. Time to break out the oscilloscope and read the disk manually, which is what they did.

Greaseweazle provides a nice display of read sectors and shows timing coming from the floppy read head. The disk in question looked good with reasonably clean timing clocks except in the area of one sector. At that point, the clocks degenerated into noise. Looking on the disk, it was easy to see why. The actual media had a small dent in it.

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