The FD-55A model
|Capacity (DOS)||180 KByte (1 x 40 x 9 x 512 = 184.320 Byte)|
|160 KByte (1 x 40 x 8 x 512 = 163.840 Byte)|
The TEAC FD-55A is the first model of the 55 series and was actually only used in the early days of CP/M and DOS, because it can only read/write on one side. Already from PC-DOS 1.1 double sided disks were supported.
Like many of these first drives, the TEAC FD-55A also has a real head loading magnet.
My TEAC FD-55A is probably an older model of the A series. The PCB does not match the one in the brochure below. There already newer LSI chips are used. Also in Vogons Wiki another PCB is shown.
The head load mechanism functions to make the head in contact with the disk when only required so as to reduce disk and magnetic head wear. This mechanism is constructed with head load solenoid, arm lifter, etc. For a single sided FDD, the head pad attached to the pad arm of the head carriage is depressed against the SIDE 1 of the disk with appropriate pressure and the disk is held with head and head pad.
TEAC FD55 Maintenance Manual, p. 304
The FD-55A has no DISK CHANGE (DC) and no READY (RY) jumper. In other words, this drive does not work on an AT, but only on a PC/XT.
There are actually only the jumpers HS, DS0, DS1, HM, DS2, DS3 and MX. My jumper settings are: DS1 and HM. That's all. But ... There is a strange jumper called DS with the settings ST or WT.
Also with the jumpers it is noticeable that this drive/PCB is different. A complete row of jumpers is missing (see: TEAC FD-55 Drive Specification, p. 128).
You have to plug the jumper on ST. If you do not, the stepper uses 80 tracks and the floppy is not usable.
With a previously formatted diskette, the table of contents can be read with DIR, but all other file accesses are incorrect. This must be the case, because this old and wide button type r/w head cannot process 80 tracks. Only the newer and narrower r/w heads of the 96 tpi drives can do this!
Chuck(G), 25.04.2019, VCF
Teac used the same stepper on all of its 40 and 80 track drives. The 55A uses the same PCB as the 55E (80T, SS), so the jumper is useful.