Teac FD-55 Series, Maintenance Manual

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and is slided along the guide shafts.
The stepping motor rotates 2 steps (3.6°) for 48tpi and one step (1.8°)
for 96tpi per one track space. To improve the continuity of the
head seek operation and precision of head positioning, hybrid type
4-phase stepping motor is adopted. This special motor is driven in
a unique manner which brought a success in reducing the head ratiation
and to obtain a highly precise positioning.
The parallelism and the distance between the shafts and the center
line of the disk, and shaft and disk themselves are precisely machined.
Also the thermal expansion of the frame, steel b e l t , carriage, etc. are
taken into consideration in the process of design so that they are
mutually offset with the expansion of the disk.
(7) Detection mechanisms
(a) File protect detection mechanism
This mechanism is constructed with an LED and a photo-transistor to
detect the existence of the write enable notch of the disk jacket.
When a disk with the notch covered is installed and the light pass
for detection is disturbed, no write or erase current will be supplied
to the read/write and erase heads and the recorded information on the
disk is protected from an erroneous input of a write command.
The LED is mounted on the PCBA DD motor servo and the photo-transistor
on the PCBA front OPT.
(b) Track 00 detection mechanism
This mechanism is constructed with a photo-interrupter for detecting
the outermost track position (track 00) of the head and the track 00
stopper which is attached to the rear side of the head carriage.
Inside tracks from the track 00 on the disk are used. Even if an
erroneous step out command is input from the track 00 position, the
command will be ignored by the internal circuit of the FDD.
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