View Full Version : Double stepping Teac FD55F 5.25 drives

September 4th, 2017, 03:30 AM
I'm rebuilding a Northstar Horizon and have some Teac FD-55F drives which work well.

Trouble is they are 80 track drives and to read my existing 40 track software disks they need to double step.

Looking around at historic forum posts (in German) it says if you remove the resistor at R19 the drive does that itself, and fitting a switch allows 40/80 track operation seamlessly.

Trouble is there is no resistor at R19 on any of my drives.

The Northstar controller seems to operate these drives well, and I have the Virtual Sector Generator board from deramp.com which allows the use of soft sectored disks transparently and have created a boot disk which works.

But I cannot read my 40 track disks.

Does anyone know how to mod the drives or CP/M to do do double stepping? I realise that disks created are not backwards compatible with true 320k drives, but that is not an issue.

September 4th, 2017, 11:05 PM
Look for a copy of DiskMaker (previously sold by New Generation Systems). The program uses a 80-Track drive to read and write over 100 different 5.25" formats, plus 8" floppy formats. No hardware modification or mechanical switches are required to switch between 40 track and 80 track formats.

Compupro included a renamed revision of this software in it's versions of CDOS. Compupro supplied the Mitsubishi M4853 80-Track DSDD 720K 5.25" drives on systems that came with a 5.25" mini-floppy disk drive.

TEAC drives (all models went through many revisions during their production runs). I sold hundreds of a couple of earlier revisions of the TEAC 3.5" 720K mini-floppy drives to people running Compupro Systems with the Disk-1A and Disk-1B. Later versions of the 720K 3.5" drive (with only had two drive select jumpers) were not plug and play, like the earlier revisions of the same drive which were plug and play (that came with four drive select jumpers).

DiskMaker was offered software only, software with Suntronics 5.25"/8" floppy controller (I've run this products in a CCS board system and a Compupro System), and as a Standalone System with two 8" and two 5.25" drives in a Case from Integrand Research with a computer system located behind the two 5.25" floppy drives.

September 5th, 2017, 12:53 AM
The old BBC B computers used these drives in a 40/80 mode. No idea now what the switch did but must be lots around who can tell you.

September 5th, 2017, 03:31 PM
Re Diskmaker, I believe that was for the IBM PC to read and write CP/M formats - I have a program for that somewhere, however remember this is a Northstar Horizon which uses 10 hard sector disks which will not read on a PC.

I did find an BBC B disk unit which has a 40/80 switch and tried it. It would not read the 40 track Northstar disks and managed to read an 80 track bootable disk just once and then gave up.

Its a work in progress ! I like the Teac drives as they were super reliable. AND I have three that work.