Radio Shack TRS-80 III User Manual

PART 1
GENERAL DESCRIPTION
A INTRODUCTION
The Disk Drive is a "MINI" Disk Memory designed for ran-
dom access data entry, storage, and retrieval applications.
These applications typically, are intell igent terminal control-
lers, micro-computers, word processing systems, data com-
munications systems, error logging, micro-program loading
and point-of-sale terminals. The Disk Drive is capable of re-
cording and reading digital data using FM, MFM or M2FM
tech niques.
IMPORTANT NOTICE
A redesigned Logic PC Board which contains both Logic
and Servo circuitry will soon be replacing the two separate
Boards used in the disk drives. A schematic of this new
Board is at the end of this section. For Theory and Parts
Lists, please refer to the TRS-80 Mini Disk Service Manual
Catalog Number 26-1160/X. '
B PHYSICAL DESCRIPTION
The electronic components are mounted on two PC Boards:
the Logic Board and the Servo Board. The Logic Board is
located above the chassis and the Power and Interface sig-
nals
are connected directly to that Board. The Servo Board
may be mounted in one of two ways, depending on the
version of the Board and type of Disk Drive. The older
version Non -linear Servo Board is mounted to the rear of
the Disk Drive on internal and external units. The newer
version Linear Servo Board is mounted to the bottom of
the Disk Drive on internal units and mounted to the rear
of the Drive the same as the non-linear Boards - on
the external units.
The spindle is belt driven by a DC motor with an integral
tachometer. The servo control circuit, pulleys and the
tachometer control the speed of the spindle. The read/write/
erase head assembly is positioned by means of a stepper
motor, split band and a pulley.
C FUNCTIONAL DESCRIPTION
The Disk Drive is fully self-contained. It consists of a spindle
drive system, a head positioning system, and read/write/erase
system.
When the front latch is opened, access is provided for the
insertion of a 5.25 inch (133.4 mm) standard diskette. The
diskette is positioned in place by plastic guides, the front
latch and a back stop.
Closing the front latch activates the cone/clamp system
which centers and clamps the diskette to the drive hub.
The drive hu b is driven at a constant speed of 300 rpm by a
servo
controlled DC motor. In operation, the magnetic head
is loaded into contact with the recording medium whenever
the front latch is closed.
A 4-phase stepper motor/band assembly and its associated
electronics position the magnetic head over the desired
track. This positioner employs a one-step rotation to cause
a
1·track linear movement. When.a write-protected diskette
is inserted into the Drive, the write-protect sensor disables
the write electronics of the Drive and an appropriate signal
is applied to the interface. (When performing a write opera·
tion, a 0.013-inch (0.33 mm) [nominal] data track is re-
corded.)
Data recovery electronics include a low-level read amplifier,
differentiator, zero-crossing detector and digitizing circuits.
No data decoding facilities are provided in the basic Drive.
The Drive is also supplied with the following sensor systems;
1. A track 00 switch which senses when the Head/
Carriage assembly is positioned at Track 00.
2. The index sensor (an LED light source and a photo-
transistor) is positioned so that when an index
hole is detected, a digital signal is generated. The
index sensor used is a high resolution device which
can distinguish holes placed close together, i.e., in-
dex -sector holes in a hard sectored diskette.
3. The write -protect sensor disables the Disk Drive
electronics whenever a write -protect tab is applied
to the diskette.
D INTERFACE CONNECTIONS
Signal connections for the external Disk Drive are made via
a
user-supplied 34 -pin flat ribbon connector. The internal
Drive uses a Radio Shack connector, Part Number AW2535.
Both of these connectors mate directly with the PC Board
connector (J 1) at the rear of the Drive. The DC power con-
nector is a four -pin connector (J2) on the Logic PC Board
on the top rear of the Drive.
The signal connector harness should be of the flat ribbon or
twisted pair type with the following characteristics:
1. Maximum length of 10 feet (3 M).
2. 22 - 24 gauge conductor compatible with the con-
nector to be used.
Power connections for external Drives should be made with
18 AWG cable. Internal Drives use the Disk DC Power
Harness, Radio Shack Part Number AW2532.
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Radio Shack TRS-80 III Specifications

General

Brand	Radio Shack
Model	TRS-80 III
Category	Desktop
Language	English