Radio Shack TRS-80 Service Manual page 100

PART 1
GENERAL DESCRIPTION
A INTRODUCTION
The Disk Drive is a "MINI" Disk Memory de$igned for ran·
dom ateen data entry. storage, and retrieval applications.
These applications typically. are intelligefl1 terminal
con~rol­
lers, micro"'Computers, word proceuing systems, data com-
munications systems, error logging, micro-pHlgram 10il(ling
and point-of·sale terminals. The Disk Orive is capable of reo
cording and reading digital data using FM, MFM or M2FM
techniques.
IMPORTANT NOTICE
A redesigned logic PC Board which contaim both Logic
and Servo cirQ.litry will soon be replillcing the two separilte
Boards used in the disk driven. A schematic of this new
Board is at tne end of this section, For Theory and Parts
lists. please refer to the
TRS-BOMini Disk !*rvice Manual,
Catalog Number 26 ·11 flJ/X.
B PHYSICAL DESCRIPTION
The electronic: compoflt'f)ts are mounted on two PC Boards:
the Logic Board and the Servo Board. The Logic Board is
located aboye Ihe chassis and the Power lind Interface sig·
nals are connceted dlrectlv to that BOillrd. The Servo Board
may be mounted in one of two ways, depending on the
version of tne Board and type of DIsk Drive. The older
Vl!fSlon Non ·Iioear Servo Board is mounted to the rear of
the Disk Drive on internal and eJCternal units. The newer
version lioear Servo Board is mounted to the bottom of
the Disk Drive on internal units and mounted 10 the rear
of the Drive - the same as the non·llnear Boards _ on
the external unin.
The
~indle
is bell driven by a DC mOlor with an integral
tachometer. The servo control circuit, pulleys and the
tachometer control thespecdof the spindle. The read/write/
erase head assembly is positioned by me"ns of a stepper
mOlor. split band llnd a pulley.
C FUNCTIONAL DESCRIPTION
The Disk Drive is fully self·contained. It consists 01 a spindle
drive system. a head posi tioning system, and read/write/crase
system.
When the front latct\ is opened, access is provided
10'
the
insenion 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 laten activate'S the cone/clamp system
which centers and clamps the diskette to the drive hub.
The drive hub is driven
at
a constant speed of 300 rpm by a
servo controlled DC motor. In operation. the magnetic head
is loaded into f.ontact with lht! rt!cording medium whenevt!r
the front latch is closed.
A 4·phase stepper motorlband assembly and its associated
ell!Ctronics position Ihe magnetic head over the desired
track. This positioner employs a one·step ro:at,on to cau$C
a '·uack lioear movement. When a write,protcetcd d,skette
is inserted into the Drive. the wrile-protect scnsor disables
(he write electronics of the Drive and an appropriate s gnal
is applied to the interface. (When perfonnrng a write oper"
lion. a 0.Ot3·inch (0.33 mml (nO'llinal! data track is re-
corded.l
Data recovery electrorliCs IIlclude a low·level read amp ifiar,
differentlator, lero cronmg detector and digitizing circuits.
No dilta decoding facIlities are provided In the basic Drive.
The Drive isalso supplied with the folloWlrlg sensor systems;
1. A track: 00 SWItch which senses when the Headl
Carriage assembly is positioned at Track eJ0.
2. The index sensor (an LED light source and a photo·
transistorl is positioned so that when an index
hole is detected, a dIQital signal is generated. The
index $Cnsor used is a high reKllution device which
can distinguish holes placed close together. i.e., ·n·
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.
o INTERFACE CONNECTIONS
S,gnal connections for the extern,,1 Disk Drive are mooe via
a user·supplied 34·pin 11,,1 ribbon connector. The internal
Drive uses a Radio Shack connector. Part Number AW2535,
Both of these connectors mate directly with the PC Board
connector (Jl) at the reor of the Drive, The DC power con·
nectar is ;} four ,pln connector (J21 on the Logic PC Board
on the top reor of the Drive.
The signal connector harnen should be of the flat ribbon or
twisted pair type with the following characteristics:
1. Maximum length of 10 feet (3M).
2. 22 - 24 gauge conductor compatible with the con-
ncetor to be used.
Power connections for external Drives should be made with
18 AWG cable. Internal Drives use the Disk DC Powel
Harnen, Radio Shack Part Number AW2532.
93