Reading flipped 5.25" disks using two Teac 5.25" drives

When trying to use a standard PC floppy drive to read flipped disks (e.g. for reading the B-side of an old C64/1541 or Apple ][ disk), it will usually fail due to the missing index signal. This was no problem for the Commodore 1541 or disk ][ drives, which did not even have a sensor for the index hole. Unfortunately, PC floppy drives require this signal in order to work properly.

Technically, the index hole is detected by a light barrier. A signal is required for the floppy drive to work, but this signal does not have to be in sync with the actual rotation of the floppy disk when reading 1541 or Apple ][ disks. If you still own two old 5.25" Teac drives, one drive might be used to provide the signal not only for itself, but also for the other floppy drive. To do so, a single-wire connection must be made between the two floppy drives. The following changes have to be done:

 - The drive providing the signal: Looking at the top of the drive you will see a photodiode that detects the signal. The two connections are labeled "C" (connector) and "E" (emitter). One wire needs to be soldered to the "C" side of this diode. There are two convenient positions where this cable might be soldered to, marked by the blue and the yellow circle in the picture. After the modification, this drive will still be able to operate by itself, and to read and write PC-formatted disks.

- The drive using the external signal: The circuit path coming from the "C" side of the photo diode needs to be cut through (see red circle in the picture). The other side of the wire needs to be connected to the pin marked with the yellow circle in the picture. After the modification, this drive will be able to read flipped 1541 and Apple ][ disks using Disk2FDI as long as it is used together with the other 5.25" drive. Normal disk access to PC-formatted disks will not work anymore.

Teac FD-55GFR modification

No guarantee can be given that this solution works for you. I have tested it using two Teac FD-55GFR drives (143U and 193U), and it seemed to work properly.

Another solution can be found here. Although it was developped for the Catweasel floppy disk controller, it should also work with Disk2FDI.

Markus Doetsch
email: markus.doetsch* (please replace * by @)