Seagate ST425 User manual

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Manhattan House
Bridge Road
Maidenhead
Berkshire SL6 8DB
Telephone:
Maidenhead
(0628) 75851
Telex:
847898 MANSKY
Facsimile:
[phone]

•
ST425 WINCHESTER DISC DRIVE
SERVICE MANUAL
June 28, 1984
Manhatt.n ~
Bridge Road
Maidenhead
BerkshireSL6 808
•
- J
Seagate. 920 Disc Drive. Scotts Valley,CA95066 • [phone]

•TABLE OF CONTENTS
SECTION
..............
PAGE
•1
l.e INTRODUCTION •• ·.~.
1.1 Specification Summary •••••••••••••••••••••••••• 2
1.1.1 Physical Specifications •••••••••••••••••• 2
1.1.2 Reliability Specifications ••••••••••••••• 3
1.1.3 Performance Specifications ••••••••••••••• 4
1.1.4 Functional Specifications •••••••••••••••• 4
2.e THEORY OF OPERATIONS ••••••••••••••••••••••••••••••• 5
2.1.3 Read/Write Heads •.••••••••••••••••••••••• 8
For mat... 0 ••••••••••••••••••••••••• 7
.............
Interface Description • ••5-6
•7·.
2.1.1 Recording Format ••
2.1.2 Track
2.1 General
•
2 •1 •4 DiBe s ••••••••••..••••••••••••••••••••••••• 8
2.1.5 Air Filtration System •••••••••••••••••••• 8
2.2 Mechanical Theory •.••••••••••••••.••••••••••••• 9
2.2.1 Track 0 Sensor .....•.•...•..........•••.. 9
2.2.2 Index Sensor ••...•..•..••••.....•..•..... 9
2.2.3 Ground Spring ••••• ·.• • • 9
2.3 Electrical Theory ••••••••••••••••••••••
2.3.1 Main Control PC Board 2e321-eel •
•le-18
.... le
2.3.2 Microprocessor Operation ••••••••••••• 11-12
2.3.3 Drive Select •••••••••••••••••••••••••••• 13
•14-15
•16-17
2.3.4 Read Operation ••••
2.3.5 Write Operation •••
·.
·.
I

2.3.6 Fault Detection ••••••••••••••••• ..... 18
2.4 Test Point Data - PC Board 20321-001 •••••.• 19-21
•••••22
- Index •••••••••
2.5 Schematics
3.0 FIELD SERVICE AND ADJUSTMENTS •
..............
................•25-32
3.1 Removals and Adjustments •••••••••••••••••••••• 26
3.1.1 Main Control PCB ••••••••••.•.••••••••••• 26
......................
·.
Front Cover LED •••
.26
•28
•27
•27
•27
.....................
.....................
·.
Cover ••••••
Frame ...•.••••••
Front
Ground Spring ••
Index Sensor •••3.1.2
3.1.3
3.1.4
3.1.5
3.1.6
3.1.7 Track oSensor ••• •28
4.0 ILLUSTRATED PARTS CATALOG - INDEX. •• 29
·.
..................... ••• 30
•••32
••• 31
..........
Component Locations ••••••••••••••
Interface Connectors ••
Exploded View •••.••••
4.1
4.2
4.3
4.4 Parts List - PC Board 20321-001 •••••••••••• 33-34
5.0 FIELD SALES OFFICES •.••••••••••••••••••••••••••••• 35
J
II

ILLUSTRATIONS
FIGURE PAGE
1.0 Test Point Layout - PC Board 20321-001 •••••••••••• 20
2.0 Test Point Timing - PC Board 20321-001 •••••••••••• 21
3.0 Interface Connectors •••••••••••••••••••••••••••••• 30
4.~ Exploded View ......•..............•..•.•........•. 31
5.0 Component Locations PC Board 20321-001 •••••••••••• 34
III

1.8 INTRODUCTION
The ST425 is Seagate's 25.52 Megabyte, 5 1/4 inch
Winchester disc drive. The ST425 has a formatted
capacity of 20.0 Megabytes.
The ST425 is the newest addition to the ST400 family of
disc drives, and has the same interface, power supply
and controller requirements as the industry standard
Seagate ST406/412/419 series.
Minislider heads and an advanced stepper motor design
enable higher track density. The new head design allows
increased bit packing which utilizes more of the disc
surface. High reliability is assured through the use of
Seagate's proven metal band-actuator, stepper motor head
positioner and a direct-drive brushless DC spindle
motor. The spindle motor assembly is aynamically
balanced and the Head Disc Assembly (HDA) is shock-
mounted to reduce vibration.
The low mass/load force of the MiniWinchester heads and
the lubricated oxide coated media provide reliable
start/stop operation. Each disc surface is read by two
read/write heads. The HDA, which includes the read/write
heads, discs and band-actuator assembly, is completely
sealed and protected by a captured-air-space
recirculation system employing a 0.3 micron absolute
filter. A filtered port permits ambient air pressure
equalization.
Thermal stabilization delays are unnecessary with the
ST425. The spindle pump assures adequate air flow and
uniform temperature distribution throughout the HDA.
This allows significantly greater off-track margin and
immediate read/write ability after power-up.
Only DC voltages (+5 and +12 V DC) are required. All
electronics are packaged a single printed circuit board.
The board is mounted outside the sealed media area
allowing easy field access without risking media
integrity. Simplification of mechanical and electrical
design provides a projected service life of more than
11,000 hours Mean Time Between Failures (MTBF).
1

5~o to 1130F (l~O to 450C)
-4eo to 14~oF (-4eo to 6eoC)
1.1 SPECIFICATION SUMMARY
1.1.1 Physical Specifications
Environmental Limits
Ambient Temperature Limits
Operating:
Non-Operating:
Maximum Temperature Gradient
Operating: 18oF/hour (l~oC/hour)
Non-Operating: Below Condensation
•
Relative Humidity:
Maximum Wet Bulb:
Maximum Elevation
Operating:
Non-Operating:
8 to 8e% non-condensing
78.8oF (260C)
-l,~ee feet to le,e~e feet
-l,~~~ feet to 3~,~~0 feet
Maximum Shock Without Incurring Physical Damage
[11 msec shock pulse, half sine wave]
Operating:
Longitudinal:
Lateral:
Vertical:
Non-Operating:
No mechanical damage
specified limits.
3GiS
5GiS
7GiS
35 GiS
will occur within the above
•
Without Incurring Soft Errors:
Incurring Physical Damage.
Maximum Vibration
Operating:
Frequency
2--22 Hz
22-5ee Hz
5~e--22 Hz
22---2 Hz
Maximum Vibration Without
Non-operating:
Frequency
2--22 Hz
22-5~~ Hz
5~~--22 Hz
22--2 Hz
.~10"
~.25
0.25
.01~"
.~4~"
l.~
1.0
.e40"
double amplitude
G (peak)
G (peak)
double amplitude
double amplitude
G (peak)
G (peak)
double amplitude
DC Power Requirements
+12 Volts +5%
+5 Volts ±5
Maximum Ripple:
1.6 A Typ., 3.5 A (at power-on)
1.1 A Typ., 1.7 A (Max.)
5e mV peak to peak (12 V, 5 V)
2

Heat Dissipation
Typical:
Maximum: 25 Watts
29 Watts
Mechanical Dimensions
Height:
Width:
Depth:
Weight:
Shipping Weight:
3.26
5.75
8.00
4.6
7.0
inches
inches
inches
pounds
pounds
Maximum
[2.1 Kg]
[3.2 Kg]
1.1.2 Reliability Specifications
MTBF:
MTTR:
PM:
The component design life
11,000 POH @250C Typ. usagt
30 minutes
Not required
is 5 years.
Read error Rates (Based on bit-jitter reduction)
*
Soft Read Errors :
**
Hard Read Errors :
Seek Errors:
1 per 1010 bits read
1 per 1012 bits read
1 per 106 seeks
~/
\
Bit-jitter reduction determines the relationship between
the leading edge of read data and the center of the data
window. The data separator must provide at least -40 dB
of bit-jitter reduction at 2F with an offset error of
1.5 nsec shift from the center of the data window.
:*Recoverable within 16 retries
Not recoverable within 16 retries
3

1.1.3 Performance Specifications
CAPACITY
Per Drive:
Per Surface:
Per Track:
Access Time:
FORMATTED
20.0 MB
5.0 MB
8,192 Bytes
UNFORMATTED
25.52 MB
6.38 MB
10,416 Bytes
Seek Times Including Settling
Single Track: 19.67 msec
Buffered Seek (from last Step pulse to SEEK COMPLETE)
Average Seek: 65 msec
Full Seek: 140 msec
Transfer Rate:
Average Latency: 5.0 MBits/sec
8.33 msec
1.1.4 Functional Specifications
Rotational Speed:
Recording Density:
Flux Density:
Track Density:
Cylinders:
Tracks:
Read/Write Heads:
Discs:
3,600 RPM ±l%
10,568 Bits per inch (Maximum)
10,568 Flux changes per inch (Maximum)
550 Tracks per inch
306
2,448
8
2
4

2.0 THEORY OF OPERATIONS
2.1 General Interface Description
The ST425 Winchester supports the Seagate ST506/412
Interface.
The interface consists of a 34 pin control connector, a
20 pin read/write connector and a 4 pin DC connector.
The 34 pin connector provides 10 control signals to the
drive and returns 5 status signals to the controller.
The 20 pin connector handles the Modified Frequency
Modulation (MFM) data to/from the drive and supplies the
drive-selected status to the controller. The 4 pin
connector provides +5 and +12 Volts DC.
In general, the control connector is "daisy-chain"
terminated throughout the user system, while the
read/write connector is terminated radially. The
following tables indicate the ST425 interface
requir'ements.
5
..

Jl/Pl - CONNECTOR PIN ASSIGNMENTS
GROUND RTN. SIGNAL
PIN PINDESCRIPTION
1
2RESERVED
3-HEAD SELECT 22
56-WRITE GATE
78*
-SEEK COMPLETE
910*-TRACK " 11 12*
-~lRITE FAULT
13 14-HEAD SELECT 20
15 16 RESERVED (To ~2 Pin 7)
17 18-HEAD SELECT 2
19 20*
-INDEX
21 22*
-READY
23 24-STEP
25 26-DRIVE SELECT 1
27 28-DRIVE SELECT 2 29 30 -DRIVE SELECT 3 31 32-DRIVE SELECT 4
33 34-DIRECTION IN
*Status enabled with DRIVE SELECT or Radial Option
J2/P2 - CONNECTOR PIN ASSIGNMENTS
GROUND RTN. SIGNAL
PIN PINDESCRIPTION
2
1-DRIVE SELECTED
43 RESERVED
65RESERVED 87RESERVED (To J1 Pin 16)
10 9NOT CONNEC£ED
12 11 GROUND
13 +MFH HRITE DATA 14 -HFH Write Data
16 15 GROUND
17 +MFr-lREAD DATA 18 -fvlFHREAD DATA
20 19 GROUND
J3/P3 - CONNECTOR PIN ASSIGNMENTS
PIN 1
PIN 2
PIN 3
PIN 4
6
+ 12 VOLTS
+ 12 VOLTS RETURN
+ 5 VOLTS RETURN
+ 5 VOLTS

IP
2.1.1 Recording Format
The ST425 uses Modified Frequency Modulation (MFM) as
the encoding method to record data. This double-density
encoding scheme increases disc capacity by replacing
clock bits with data bits. Clock bits are written only
when data bits are not present in both the preceding and
current bit cell. Clock bits are written at the
beginning of the bit cell, while data bits are written
in the midd Ie.
Due to predictable bit-shift phenomena, the ST425
requires pre-compensation of write data on cylinders 128
through 305. This function must be provided by the
controller to ensure data integrity at the specified
error rate. The data pattern determines which bits must
be pre-compensated. The recommended amount of pre-
compensation is 12 nsec for both early and late written
bits. All other data patterns are written on time.
2.1.2 Track Format
The ST425 uses a slightly modified version of the IBN
System-34 double-density format. This format is common
to many industry standard floppy-disc drives.
When formatted, each sector is identified by a unique
identification field, containing cylinder, head and
sector information, address mark and error checking
polynomials. The Seagate format uses Cyclic Redundancy
Checking (CRC) for error correction. This format also
allows for a plus or minus speed variation of
aproximately 3%. The specification for spindle speed
variation is 1% over the specified environmental and
power limits.
7

2.1.3 Read/Write Heads
When operational, the read/write heads fly on an air
bearing created by the rotating disc. There is no
dedicated landing zone. The head and flexure (supporting
arm) are designed for contact start/stop operation •
The Winchester heads are loaded toward the disc surface
at 9.5 ~l grams. This is a typical value to allow the
required stability in all operating conditions. A
typical flying height measured at an inner radius is 15
±2 microinches. At an outer radius the height is 25 ~3
microinches.
The head/flexure assembly incorporates a low mass
design that is resistive to head and/or media damage.
2.1.4 Discs
The ST425 employs two non-removable double-sided 5 1/4
inch discs. These discs are designed using current iron
oxide technology. Disc dimensions are 40mm inside
diameter by l30mm,outside diameter. The thickness of the
magnetic coating is 20 microinches at the ID and
increases linearly to 40 microinches at the ODe
The disc surface is coated with a flourocarbon lubricant
25 to 55 Angstroms in thickness. The lubricant has
sufficient abrasion resistance to withstand a minimum of
10,000 start/stop cycles.
2.1.5 Air Filtration System
The ST425 incorporates a captured-air-space air
filtration system. The 0.3 micron filter maintains Class
100 standards within the sealed Head Disc Assembly (HDA)
and requires no maintenance during the life of the
drive. A filtered port allows ambient pressure
equalization. During normal operation there is no
measurable air flow between the HDA and the outside
environment.
2.2 Mechanical Theory
2.2.1 Track 0 Sensor
The Track 0 optical interrupter provides an output
whenever the Winchester heads are positioned over
Cylinder Zero. This signal is used by the internal drive
control electronics during the power-on/auto-recalibrate
routine. The Track 0 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
8
..
I-
/-
..:.

2.2 Mechanical Theory
2.2.1 Track ~ Sensor
The Track 0 optical interrupter provides an output
whenever the Winchester heads are positioned over
Cylinder Zero. This signal is used by the internal drive
control electronics during the power-on/auto-recalibrate
routine. The Track 0 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 0 optical interrupter incorporates an infrared LED
and an infrared sensitive photo-transistor. When the
heads are positioned at Track 0, an interrupter arm
attached to the stepper motor shaft breaks the light
beam between the two components of the sensor. The
sensor will output a valid Track 0 signal as long as the
beam remains broken.
2.2.2 Index Sensor
Once each revolution the Index Sensor provides an index
pulse to the microprocessor for recalibration. The ST425
Index Sensor is of the reluctance transducer type. The
sensor incorprates a built-in preamplifier. The case of
the sensor is grounded, which ties the drive DC returns
to the drive casting.
The hub of the spindle motor has two metal tabs
attached. One is ferrous and the other, which is mounted
1800 is non-magnetic. Each revolution of the spindle
motor causes the ferrous tab to rotate past the sensor,
thereby inducing a pulse.
Note: Please do not attempt to set the Index Sensor gap
without referring to the appropriate section in the
field service section of this manual.
2.2.3 Ground Spring
The ST425 incorporates a grounding contact between the
spindle motor hub and the PC Board ground plane.
9

2.3 Electrical Theory - Main Control" PC Board 20321-001
2.3.1 Motor Speed Control
Block Diagram -"
HALL
SENSOR SPINDLE MOTOR CONTROL
LSI \lCSB)
MOTOR SPEED MOTOR
-
SPINDLE
INTEGRATOR DRIVERS
MOTOR
MOTOR
CURRENT LIMITER
DYNAMIC BRAKE
VOLTAGE
Refer to schematic on page 23.
The sequence of normal operations. is as follows:
Hall Effect Transducer
Located inside the spindle hub, This magnetic transducer
senses spindle position and provides dynamic feedback
proportional to the speed of the motor. Two complete
square waves are generated each motor revolution. This
positional information is supplied to the spindle motor
control LSI (IC 5B,pin 3). To prevent both phases of the
motor from being selected simultaneously, the motor
control LSI inverts the Hall input to coil A.
Spindle Motor Control LSI
When current is applied, the spindle motor control LSI
sets the motor speed to 3,600 RPM nominal. This LSI
integrates and transforms the error messages from the
Hall effect transducer. Using this information, it
outputs the correct current flow each revolution and
corrects the motor phase driver at output pins 6 and 7.
When power is interrupted, the Motor Control LSI shorts
both phases of the motor to ground, allowing the motor
generated back-EMF to bring the spindle to a stop.
10

2.3.2 Microprocessor Operation
Block Diagram - ..
MICROPROCESSOR
\6500/
WRITE CIRCUIT
SPINDLE MOTOR
IWR
MOTOR VOLTAGE
CONTROLLER
SEEK COMPLETE
READY
TRACK 0
CONTROLLER
STEP DIRECTION
HEAD SELECT 0, 1,2
DRIVE
SELECT
TRACK 0
CIRCUIT
INDEX
CIRCUIT
CONTROLLER
Functional Description -
The ST425 uses a microprocessor to monitor and control
internal drive functions and host interface lines. The
MPU has only three active modes: Initializing, Seeking
or Waiting.
At power-on, the MPU initializes the stepper circuit to
phase A and resets all interface lines under its
control. Power is then applied to the Spindle Motor
Control LSI and the index line is monitored for spindle
rotation. If rotation is not sensed within 15 seconds,
the MPU assumes a problem and removes power.
As the drive spins-up, 66~ revolutions are counted
before the MPU assumes that the drive is "at speed," and
initiates recalibration. If the heads are not over Track
~, the drive will step at 3 msec per track. When both
mechanical Track ~ and electrical phase A are present,
the drive is at true Track ~ and stepping will cease.
Within 2~ msec both SEEK COMPLETE, TRACK ~ and READY
will go true, and the drive is then ready to accept
inputs from the controller.
When in the idle mode, the MPU loops, waiting for step
pulses. The MPU also monitors its RESET line (pin 39)
for a low to high signal,from IC 4F, which causes the
MPU to reinitialize (see above).
11
~;f:~j'~-~~~"··'-"·'·~'·-·'~""">~·-····~~h"""

Upon receiving a Step pulse, the MPU pauses for 599
usec, to allow for additional pulses, before executing
the seek operation. Every incoming pulse resets the 599
usec timer. The seek operation will not begin until the
last pulse is received.
When seeking, the MPU evaluates the number of track~ to
be covered and searches the PROM for the most efficient
path. Seeks longer than seven tracks involve a complex
acceleration/deceleration routine to optimize the
motor and carriage characteristics. Steps are
accomplished by setting IC 2B to sequential phases. It
provides both a current source and sink with the motor
winding. Near the end of a seek, 2D and 2E are set to
provide additional current to offset expected
hysteresis.
Upon completion of a seek operation, settling time is
calculated based upon the length of seek, and the
interface line is activated in the specified time
period. With SEEK COMPLETE, the MPU returns to the idle
mode.
Whenever a seek ~peration crosses the write current
switch boundary at Track 126, the microprocessor reduces
the write current to the heads during write operations.
I~
:' ;
,.
12
.;.'

2.3.3 Drive Selection
Block Diagram -
TO INTERFACE
LINE DRIVER
FROM INTERFACE
DRIVE SELECTED
-LINE RECEIVER
TRACK\!
-STEP PULSES
DRIVE SELECT 1 DRIVE SELECT 2 READY
DRIVE SELECT 3 DRIVE SELECT 4 -
DIRECTION
SEEK COMPLETE
•WRITE FAULT
-ACTIVITY LED
INTERNAL INDEX
,.
Functional Desciiption
DRIVE SELECT serves only tb gate other signals to or
from the drive interface. Without DRIVE SELECT, the
drive cannot Read, Write or Seek.
13
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Jit'.. ".·····!{;th~~;\ill;~)i.,·".,t~iJi.s;i·..'.'

2.3.4 Read Operation
Block Diagram - .
HEAD SELECT
tlnlerfacel
READIWRITE
HEADS
LSI
PREAMP LOW PASS FILTER READ DAiA CONVERSION
READ/WRITE LSI tiC 6HI MFM READ DATA
(Inlerfacel
,
Functional Description -
Head Select
The binary decoder, IC 2F, selects the desired head
based on the status of the 3 head select lines. If the
DC voltages are too low (possibly causing an inaccurate
write operation), pin 12 will force the decoder to
choose a nonexistent head. During read operations the
head center tap is set at approximately 5 Volts by the
Read/Write LSI, IC 6H, pin 27. By referencing eto
+5 Volts, actual ground appears as -5 Volts,which
eliminates the necessity of a negative power source
normally required by the LSI preamp, IC 4G.
LSI Preamp
With the head center tap active, data from the selected
head will flow into the preamp. This preamp amplifies
the read signal and also acts as a high pass filter.
Low Pass Filter
This filter network attenuates high frequency noise,
which is outside the normal data signal range.
14
~.;~'.'.~~~'....,.~',

L·
Read Data Conversion
Amplified data enters the Read/Write LSI (IC 6H) at
pins 1 and 2 and exits as high speed MFM (differential)
read data at pins 17 and 18. The Read/write LSI
functions are:
1. Read data shifted 900'
2. Analog to digital conversion
3. Erroneous data bits removed
4. Conversion of digital data to MFM (differential) data
providing immunity to common mode noise during
transmission
.)
15
~..~...•. ,.,.."