Seagate Technology ST-406 User manual

SEAGATE TECHNOLOGY
ST-406/412 MICROWINCHESTER
SERVICE MANUAL
JANUARY 14, 1983
' .
360 El Pueblo Road• Scotts Valley, CA 95066 •·Phone: {408) 438-6550

PREFACE
This document refers to the Seagate Technology OEM Maintenance Manual for
the ST-400 product family. The scope of this manual reflects the type of
maintenance philosophy selected for this product. Throughout this manual the
product family is referred to as the ST-4XX series. Current products
specifically covered by this document include the following.
ST-406
ST-412 6
.-38MB·,
12.76MB,
SMB formatted
lOMB formatted
The purpose of this manual is to provide the Wang-trained Customer
Engineer (CE) with instructions to operate, troubleshoot and repair the ST-400
product family.

TABLE OF CONTENTS
SECTION
1.0
2.0
INTR.ODUCTION •• ••••••••••••••••••••••••••••••••••••••••••••••• •1
1.1
1.2
General Description •••••••••••••••••••••••••••••••••••••• !
Specification Summary •••••••••••••••••••••••••••••••••••• 2
1.2.1
1.2.2
1.2 .3
1.2.4
Physical . ......................................... 2
Reliability ••••••••••••••••••••••••••••••••••••••• 2
Performance ••••••••••••••••••••••••••••••••••••••• 3
Functional •••••••••••••••••••••••••••••••••••••••• 3
THEORY OF OPERATIONS •••••••••••••••••••••••••••••••••••••••••• 4
2.1 General ...............................................•.. 4
2.2
2.3
2 .1.1
2.1.2
2.1.3
Interface Description ••••••••••••••••••.••••••••••• 4
Recording Format •••••••••••••••••••••••••••••••••• 6
Track Format•• ••• ••• • •••• •• •• • •••• •• ••• ••• •• •• •• ••6
2.1.4 Winchester Heads •••••••••••••••••••••••••••••••••• 7
2.1.5 Discs .................................•........... 7
2.1.6 Air Filtration System ••••••••••••••••••••••••••••• 7
Mechanical Theory •••••••••••••••••••••••••••••••••••••••• 8
2.2.1
2.2.2
2.2.3
2.2.4
Track G Sensor •••••••••••••••••••••••••••••••••••• 8
Index Sensor •••••••••••••••••••••••••••• ···•••··· .8
Ground Spring •••••••••••••••••••••••• •••••••••••••8
Spindle Brake ••••••••••••••••••••••••••••••••••••• 9
Electrical Theory/Flowchart ••••••••••••••••••••••••••••• 10
2.3.l Motor Speed Control PCB P/N 20099 ••••••••••••••• 10
2.3.2
Motor Speed Control PCB
P/N 20136 ••••••••••••••• 12
i

SECTION
2.4
2.5
2.3.3
2.3.4
2.3.5
2.3.6
2.3.7
MPU Operation •••••••••••••••••••••••••••••••••••• 14
Drive Select ••••••••••••••••••••••••••••••••••••• 15
Read Operation ••••••••••••••••••••••••••••••••••• 16
Write Operation •••••••••••••••••••••••••••••••••• 18
Fault Detection •••••••••••••••••••••••••••••••••• 19
Test Point Description •••••••••••••••••••••••••••••••••• 21
2.4.1
2.4.2
Main Control PCB P/N 20096 ••••••••••••••••••••••• 21
Main Control PCB P/N 20110 ••••••••••••••••••••••• 24
Schematics •••••••••••••••••••••••••••••••••••••••••••••• 27
2.5.1
Main
Control PCB P/N 20096 ••• ••••••••••••••••••• 2·8
2.5.2
Main Control PCB
P/N
20110 .....•••..•.•.•..•.... 30
2.5.3 Motor Control PCB
P/N
20099 .......••.••.•....... 32
2.5.4
Motor Control PCB
P/N
20136 .•.•.•.•••••••..••.•• 33
3.0
MAINTENANCE/REPAIR ••••••••••••••••••••••••••••••••••••••••••• 34
3.1
3.2
Introduction •••••••••••••••••••••••••••••••••••••••••••• 34
Removals And Adjustments •••••••••••••••••••••••••••••••• 35
3.2.1
3.2.2
3.2.3
3.2.4
3.2.5
3.2.6
3.2.7
3.2.8
3.2.9
Main Control PCB ••••••••••••••••••••••••••••••••• 35
Motor Control PCB •••••••••••••••••••••••••••••••• 35
Spindle Brake •••••••••••••••••••••••••••••••••••• 36
Index Sensor ••••••••••••••••••••••••••••••••••••• 36
Ground Spring •••••••••••••••••••••••••••••••••••• 37
Front Cover •••••••••••••••••••••••••••••••••••••• 37
Front Cover LED •••••••••••••••••••••••••••••••••• 38
Side Frame ••••••••••••••••••••••••••••••••••••••• 38
Track GSensor ••••••••••••••••••••••••••••••••••• 39
ii
~
·~

SECTION
4.0 ILLUSTRATED PARTS CATALOG •••••••••••••••••••••••••••••••••••• 40
4.1
Physical Locations •••••••••••••••••••••••••••••••••••••• 40
4.1.1
Drive Exploded View, 4
point
suspension •••••••••• 41
4.1.2
Drive Exploded View, 3
point
suspension •••••••••• 42
4.1.3
Connectors Exploded View ••••••••••••••••••••••••• 43
4.2
Component Locations ••••••••••••••••••••••••••••••••••••• 44
4.2.1
Main Control
PCB P/N
20096 .•..•••••••••••••••••• 45
4.2.2
Main Control
PCB P/N
20110 •..•..•.•...•.....••.• 46
4.2.3 Motor Control
PCB
P/N
20099 •••••••••••••••••• ~ •• 47
4.2.4 Motor Control PCB
P/N
20136 •.......•..•.•..••••• 48
~
4.3
Parts
Lists ••••••••••••••••••••••••••••••••••••••••••••• 49
4.3.1 Main
Control PCB
P/N 20096
.•.......•••.••••••..• 50
4.3.2
Main Control PCB P/N
20110 ........•...•...•..•.. 52
4.3.3 Motor Control
PCB P/N
20099 ..•...•.•...••..•.•.. 54
4.3.4 Motor
Control PCB P/N
20136 ..•.....•••..•••••..• 55
4.3.5
Spare Parts List ••••••••••••••••••••••••••••••••• 56
iii

LIST OF ILLUSTRATIONS
FIGURE
2.1 Tes.t
Point Layout -
PCB
P/N
20096 ••••••••••••••••••••••••••• 22
2.2 Test
Point
1 &2 Timing - PCB
P/N
20096 ••••••••••••••••••••• 23
2.3
Test Point
3 &4 Timing -
PCB P/N 20096 ••••••••••••••••••••• 23
2.4
Test Point 6 Timing -
PCB P/N
20096 ..............•........... 23
2.5 Test Point Layout - PCB P/N 20110 ••••••••••••••••••••••••••• 25
2.6 Test Point 7 &8 - PCB P/N 20110 •••••••••••••••••••••••••••• 26
2.7 Test Point 11 &13 - PCB P/N 20110 •••••••••••••••••••••••••• 26
2.8 Test Point 4 - PCB P/N 20110 •••••••••••••••••••••••••••••••• 26
iv

Introduction
ST-406/412 Service Manual
1.0 IBTllODUCTIOB
1.1 General Description
The ST-400 series is the second generation of 5-1/4 inch micro-Winchester
disc drives from Seagate Technology. Based on the proven design of the
world's first micro-Winchester, the ST-506, the new series features
greater capacity, performance, and reliability, while maintaining
compatibility in form factor and controller design with the earlier
model.
Manganese-zinc heads and advanced stepper motor design enable higher
track density. The new head design al~ows increased bit packing,
utilizing more of the disc surface and double the number of cylinders.
High reliability is assured through the use of a proven metal band
actuator, open-loop stepper head positioner, and direct drive brushless
DC drive motor. A dynamically balanced motor/spindle assembly and a
shock mounted baseplate reduce vibration.
The low mass and load force of Winchester heads and the lubricated, oxide
coated media on an aluminum substrate, provide reliable contact
start/stop operation. Each disc surface is read by a dedicated
read/write head. Fully enclosed discs, heads, and band actuator are
protected by an integral recirculation air system with a 0.3 micron
absolute filter. Integral to the filter is a port which permits pressure
equalization with ambient air while preventing entry of contaminants.
Thermal stabilization delays are not necessary with the ST-400 series.
The patented spindle pump assures adequate air flow and uniform
temperature distribution throughout the sealed head and disc areas. The
stepper and spindle motors are thermally isolated, resulting in a very
low temperature rise, providing significantly greater off-track margin
and immediate read and ~ite operations after,J~W~r up.
Only DC voltages (+12 and +5VDC) are required. All electronics are
packaged on two printed circuit boards. The boards are mounted outside
the sealed media area, allowing quick ac~ess.and easy field repair
without risking media integrity. Simplification of mechanical and
electrical design provides a projected service life of more than 11,000
hours MTBF. An advanced stepper motor, metal band actuator and the
onboard microcomputer's buffered seek mode improve average access time.
The ST-400 series bas the same physical dimensions, recording format,
transfer rate, interface, power supply and controller requirements as the
industry standard Seagate ST-506. Controllers are available from several
sources that provide for interfacing the ST-400 series micro-Winchesters
with most popular microcomputers.
Seagate Technology 1
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.Introduction ST-406/412 Service Manual
1.2 Specification Summary
1.2.1 Physical Specifications
Environmental Limits
Ambient Temperature
Operating:
Non-operating:
Temperature Gradient
Operating:
Non-operating:
Relative Humidity:
Maximum Wet Bulb:
Maximum elevation
Operating:
Non-operating:
Shock
400 to 1220F (40 to 500C)
-400 to 1400F (-400 to 600C)
180F/hour or lOOC/hour
Below condensation
8 to 80% non-condensing
78.SOF (260C)
10,000 feet
-1,000 to 30,000 feet
Operating: lOG's*
Non-operating: 20G's*
*No mechanical damage will occur within these limits.
D.C. Power Requirements
+12V .±,.5%, 1.6A typical, 3.5A (At power on)
+5V .±,.5%, I.IA typical, 1.7A (Maximum)
Maximum Ripple: 50mV peak to peak (12V, 5V)
Mechanical Dimensions
Height:
Width:
Depth:
Weight:
Shipping Weight:
Heat Dissipation
Typical:
Maximum:
3.25 inches
5.75 inches
8.00 inches
4.6 pounds (2.lKg)
9.0 pounds (4.lKg)
25 watts
32 watts
1.2.2 Reliability Specifications
MTBF: 11,000 POH, typical usage
MTTR: 30 minutes
PM: Not required
Component design life: 5 years
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Introduction
ST-406/412 Service Manual
Error Rates
Soft Read Errors*: 1 per 1010 bits read
Hard Read Errors**: 1 per 1012 bits read
Seek Errors: 1 per 106 seeks
*Recoverable within 16 retries
**Not recoverable within 16 retries
1.2.3 Performance Specifications
Capacity
Unformatted
Per Drive:
Per Surface:
Per Track:
Access Time
Average*:
Maximum*:
Single Track Seek/Settle:
*using buffered seek (includes
Transfer Rate:
Average Latency:
1.2.4 Functional Specifications
Rotational Speed:
Recording Density:
Flux Density:
Track Density:
Cylinders:
Tracks:
Read/Write Heads:
Discs:
Seagate Technology 3
Model Number
ST-406 ST-412
6.38 MB
3 .19 MB
10 ,416 Bytes
85ms
205ms
<16.67ms
settling)
12.76 MB
3.19 MB
10,416 Bytes
85ms
205ms
<16 .67ms
5.0 Mbits/sec 5.0 Mbits/sec
8.33 ms
3,600 RPM±_l%
9,074 BPI
9,074 FCI
345 TPI
306
612
2
1
8.33 ms
3,600 RPM ±_1%
9,074 BPI Max
9,074 FCI Max
345 TPI
306
1224
4
2
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Introduction
ST-406/412 Service Manual
2.0 TllEORY OF OPERATIORS
2.1 General
2.1.1 Interface Description
The ST-400 Family supports the industry standard ST-506 interface
developed by Seagate Technology. This interface provides many
floppy disc similarities in addition to supporting the increased
performance requirements of the 5 1/4" Winchester type products.
The interface consists of a 34 pin Control connector, 20 pin
Read/Write connector, and a 4 pin DC Power connector. The 34 pin
connector provides 10 control signals to the drive and returns 5
status signals to the drive controller. The 20 pin connector
handles the MFM data to and from the drive and also supports the
-Drive Selected status to the controller. The 4 pin connector
provides the +5 and +12Volt supply requirements.
In general, the Control connector is "daisy-chain" terminated
throughout the user system while the Read/Write connector is
terminated radially. The following tables show the ST-4XX interface
requirements.
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Theory of Operations
ST-406/412 Service Manual
JI/Pl-CONNECTOR PIN ASSIGNMENTS
GND RTN
SIGNAL SIGNAL
PIN PIN
DIRECTION DESCRIPTION
1 2 Reserved
3 4
In Reserved (Head 22)
5 6
In -Write Gate
7 8
Out
-Seek Complete
9 10
Out
-Track ~
11
12 Out -Write
Fault
13 14
In
-Head Select 20
15
16 Reserved (To J2 Pin 7)
17
18 In -Head Select 21
19
20 Out -Index
21
22
Out -Ready
23
24 In -Step
25
26 In
-Drive
Select
1
27 28 In
-Drive
Select
2
29 30 In
-Drive
Select
3
31
32
In
-Drive
Select 4
~
33 34
In -Direction In
J2/P2-CONNECTOR PIN ASSIGNMENTS
GND RTN
SIGNAL SIGNAL
PIN
PIN DIRECTION
DESCRIPTION
2 1
Out
-Drive Selected
4 3 Reserved
6 5 Reserved
8 7 Reserved
(To Jl Pin 16)
10
9 Reserved
12 11 Ground
13
In +MFM Write Data
14
In
-MFM Write Data
16
15 Ground
17
Out +MFM Read Data
18
Out -MFM Read Data
20 19 Ground
J3/P3-CONNECTOR PIN ASSIGNMENTS
GND RTN
SIGNAL SIGNAL
PIN
PIN
DIRECTION DESCRIPTION
2 1
+12 Volts
DC
3 4 + 5
Volts
DC
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Theory of Operations
ST-406/412 Service Manual
2.1.2 Recording Format
The ST-4XX uses modified frequency modulation (MFM) as the encoding
method implemented to record data on the drive. This double-density
encoding scheme increases disc data capacity by replacing clock bits
with data bits. Clock bits are written only when data bits are not
present in both the preceding and the current bit cell. Clock bits
are written at the beginning of the bit cell, while data bits are
written in the middle.
Due to predictable bit-shift phenomena, write data may require
precompensation. This function must be provided by the controller to
insure data integrity at the specified error rate. The ST-4XX
requires precompensation of write data on cylinders 128 through 305.
The data pattern determines which bits must be precompensated. The
recommended amount of this precompensation is 12ns for both early
and late written bits. All other data patterns are written on time.
2.1.3 Track Format
The track format used on the Seagate ST-4XX disc drive is a slightly
modified version of the IBM System 34 double density format. This
format is common to many industry standard floppy disc drives. All
ST-4XX drives are formatted at the factory before shipping.
As formatted, each sector is identified by an identification field
that is different than any other on the drive. The ID field contains
cylinder, head, and sector information as well as address mark and
error checking polynomials. The Seagate format uses Cyclic
Redundancy Checking (CRC) for error evaluation. The format also
allows for a plus or minus speed variation of approximately 3%. The
ST-4XX specification for spindle speed variation is 1% over the
specified environment and power limits.
Seagate Technology 6
01 /14/83
.~

Theory of Operations
ST-406/412 Service Manual
2.1.4 Winchester Heads
The Seagate Technology ST-4XX uses Manganese/Zinc Ferrite Winchester
head technology. The head/flexture (supporting arm) assembly is
designed for contact start-stop operation. Bit packing density is
9074 BPI and the radial track density is 345 TPI. The heads, when
operational, are supported on an air bearing created by the rotating
disc.
The Winchester heads used are loaded toward the disc surface at 9.5
grams. This is the typical value to allow required stability in all
operating conditions. The flying height of the heads at the
innermost cylinder is 19 microinches with a tolerance of ±3
microinches. The flying height of the heads at the outermost
cylinder is 24 microinches, .±.3 microinches.
The load force of 9.5 grams is sufficient enough so that various
mounting orientations of the disc drive will not affect the flying
height of the Winchester heads to any significant degree.
Additionally, the head/flexture assembly incorporates an extremely
low mass design that is resistive to head and/or media damage when
shipping.
2.1.5 Discs
The ST-4XX disc drive uses non-removable double sided 5 1/4 inch
discs as the recording media. The discs are designed upon current
iron oxide technology. The actual disc dimensions are 40mm inside
diameter by 130mm outside diameter. Thickness of the magnetic
coating is 20 to 40 microinches increasing linearly from the inside
diameter to the outside diameter.
The disc surface is coated with a Teflon lubricant 40 to 60
angstroms in thickness. This value is equivalent to a uniform
monomolecular film. The disc lubricant has sufficient abrasion
resistance to withstand a minimum of 10,000 start/stop cycles. The
magnetic discs have a life expectancy of 5 years.
2.1.6 Air Filtration System
All drives manufactured by Seagate Technology incorporate an
integral air filtration system. No maintenance or adjustments are
needed throughout the life of the drive. The integral 0.3 micron
air filter performs two functions. First, the filter maintains Class
100 standards inside the sealed Head/Disc Assembly throughout the
life of the drive. Second, an auxillary port allows pressure
equalization with ambient air. During normal operation there is no
measurable air flow between the HDA and the outside environment.
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Theory of Operations
ST-406/412 Service Manual
2.2 Mechanical
2.2.1 Track GSensor
The Track 0 optical interrupter provides an output whenever the
Winchester heads are positioned over cylinder a. This signal is
used by the internal drive control electronics during the power-on
auto-recalibrate routine. The Track a signal is also output to the
drive interface for use by the controller. Note that the signal at
the interface is really Track 0/Phase "A".
The Track a optical interrupter incorporates an infrared
light-emitting-diode and an infrared sensitive photo-transistor.
When the heads are positioned at cylinder~, an interrupter arm
attached to the stepper motor shaft mechanically breaks the light
bea~ between the two components of the sensor. The sensor will
output a valid Track 0 signal as long as the light beam remains
broken.
2.2.2 Index Sensor
Once each revolution the Index sensor provides an index pulse to the
microprocessor for recalibration, and to the interface of the ST-4XX
drive. The Index pulse width depends on the specific Main Control
PCB used on the drive: see section 2.4.
The Index sensor used on the ST-4XX drive is of the reluctance
transducer type. This cylindrical sensor incorporates a built-in
preamplifier. The case of the sensor is grounded electrically which
ties the drive DC returns to the drive casting.
The hub of the spindle motor has two metal tabs attached; one is of
a ferrous composition and the other is non-magnetic. Each
revolution of the spindle motor causes the ferrous tab to pass
within close proximity of the Index sensor, therefore inducing the
pulse output.
Note: The dimension between the spindle motor tab and the Index
sensor is set to 30 mils (.030") at the factory.
2.2.3 Ground Spring
The ST-4XX incorporates a grounding contact between the spindle
motor hub and the drive casting. This ground spring performs the
task of removing all unwanted static electrical charges from the
spindle motor hub.
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Theory of Operations
ST-406/412 Service Manual
2.2.4 Spindle Brake
Note: Newer ST-4XX disc drives do not use the Spindle Brake. A
revised Motor Control PCB incorporates dynamic braking. In these
units, the Motor Control PCB uses the reverse EMF generated by the
spindle motor to slow the discs (See section 2.3.2).
The earlier ST-4XX uses an electromechanical brake to slow the
spindle motor when DC power is removed. The spindle brake is
energized directly from the +12V supply. When +12V is removed from
the drive, the brake engages against the spindle motor hub to slow
the motor.
The pad contact material is of a rubber-cork composition with wear
life designed to exceed 20,000 cycles. When energized, the brake
will draw a maximum current of 267 milliamps.
The brake must be adjusted so that the contour of the pad contact
matches the spindle motor hub. When disengaged, the dimension
between the spindle motor hub and the pad contact should be set at
I0 mil s ( •0I0") •
Seagate Technology 9 01/14/83

Theory of Operations
ST-406/412 Service Manual
2.3 Electrical Theory/Flowchart
I
I
I
I
2.3.1 Motor Speed Control PCB P/N 20099
Block Diagram-
I I I I I
_I
COMPARATOR
l_I
STARTER
l_I
INTEGRATOR
I I I I I I
_ I_
__ I_
I I I
HALL
I I
CURRENT
I
SPINDLE
SENSOR
I I
CONTROL
I
MOTOR
I I I
Functional Description-(refer to the schematic on page 3t)
Initially, when power is first applied, the disk is stationary and
the Hall effect transistor (located inside the spindle motor) will
output a high or low level, depending on the physical position of
the motor. This DC level will keep Ql turned off, allowing CS to
charge up. Pin 1 of Comparator A2 will output a low level that
travels through R12 and forces pin 7 of A2 high. As a result, Al
will be off and maximum current will flow into the coil selected by
the level of the Hall effect sensor.
As the motor speeds up, the Hall effect becomes a square wave
responsible for both selecting the motor coil to receive current and
controlling the amount of current applied. Current is supplied
alternately to coils A and B as the Hall device senses the motors
physical position. Depending on the time between high going edges
of the Hall effect sensor, Ql will be turned off long enough for CS
to charge to more than 4 volts and force pin 1 of Comparator A2 low.
This low pulse will turn on pin 7 of Al whose resulting 6 volt
output pulse will direct pin 7 of Integrator A2 to allow more
current to enter the motor coils.
The sequence of normal operation is as follows:
1) The Hall effect sensor relays speed and position information to
the speed error comparator and to the current controller.
2) The speed error comparator, pin 1 of A2, generates a low spike
whose duration is dependent on the speed error. A slow speed will
result in the low pulse being longer.
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Theory of Operations
ST-406/412 Service Manual
3) The speed error information enters the starting circuit which
functions to pass a low frequency signal directly to the integrator
indicating maximum error during start up. The starting circuit also
inverts the speed error information and combines it with a carrier
that properly biases the integrator.
4) Pin 7 of Integrator A2 translates the error information into a
level appropriate for biasing both halves of IC Al, which functions
to control the current source.
5) The current control, IC A3, supplies the proper amount of current
for attaining proper speed as directed by IC Al.
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2.3.2 Motor Speed Control/Dynamic Brake PCB P/N 20136
Block Diagram -
I I I
__ I COMPARATOR I STARTER I I INTEGRATOR
I I____ l ____ l-1 ___ _
_ I_ __I __
I I I I I
I HALL l ____________ I CURRENT l __ I SPINDLE
I SENSOR I I CONTROL I I MOTOR
I I I I I __ _
_ I_ __I_ __
I I I I
I POWER I I DARLINTON I
I .SENSOR I I SHORT I
I I I_ I
Functional Description-(refer to the schematic on page 33)
Initially, when power is first applied, the disk is stationary and
the Hall effect transistor (located inside the spindle motor) will
output a high or low level, depending on the physical position of
the motor. This DC level will keep Ql turned off, allowing C5 to
charge up. Pin 1 of Comparator 2A will output a low level that
travels through Rl2 and forces pin 7 of 2A high. As a result, lA
will be off and maximum current will flow into the coil selected by
the level of the Hall effect sensor. Q2 acts as a limiter to keep
the starting current down to 3.5 Amps max.
As the motor speeds up, The Hall effect becomes a square wave
responsible for both selecting the motor coil to receive current and
controlling the amount of current applied. Current is applied
alternately to coils A and B as the Hall device senses the motor
position. Depending on the time between high going edges of the Hall
effect sensor, Ql will be turned off long enough for CS to charge to
more than 4 volts and force pin 1 of Comparator 2A low. This low
pulse will turn on pin 7 of lA whose resulting 6 volt output pulse
will direct pin 7 of Integrator 2A to allow more current to enter
the motor coils.
The sequence of normal operation is as follows:
1) The Hall effect sensor relays speed and position information to
the speed error comparator and to the current controller.
2) The speed error comparator, pin 1 of 2A, generates a low spike
whose duration is independent of the speed error. A slow speed will
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ST-406/412 Service Manual
result in the low pulse being longer.
3) The speed error information enters the starting circuit which
functions to pass a low frequency signal directly to the integrator
indicating maximum error during start up. The starting circuit also
inverts the speed error information and combines it with a carrier
that properly biases the integrator.
4) Pin 7 of Integrator 2A translates the error information into a
level appropriate for biasing both halves of IC lA, which functions
to control the current source.
5) The current control, QJ and Q4, supplies the proper amount of
current for attaining proper speed as directed by IC lA.
Functional description-Dynamic Brake (schematic page 34)
On power up, Cl3 is charged to just below 12 volts and Q7 remains
off. When the power is shut off or drops below 12 volts for a
period, Cl3 discharges through Q7 turning on the darlington pair, Q5
and Q6. This effectively shorts the motor coils and magnetically
brakes the motor.
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2.3.3 MPU Operation
Block Diagram-
BOST
STEPPER MOTOR
I
STEP
l_I
I
TRACK 0
SENSOR
DRIVE SELECT MPU
I
I __
STATUS LINES
I_
l_I
RALL SENSOR
(SEEK COMPLETE,
I I I
(Spindle Motor)
TRACK 0, I I
WRITE FAULT,
I
INDEX,READY)
I
WRITE FAULT
Functional Description-
The ST-4XX family uses a microprocessor to monitor most of the drive
functions and interface with the host controller. Primary processor
duties are as follows:
1. Count the 666 revolutions required after power up for the "up
to speed" function.
2. Monitors the TRACK ~ sensor and automatically recalibrates
the drive to TRACK~-
3. Accepts step pulses, performs necessary buffering of the
pulses, then determines the proper algorithm to perform the stepping
required.
4. When the DRIVE SELECT line is active; receives control
signals from the host controller and gates status signals in return
(See the Interface Description, section 2.1.1).
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