Shugart SA850 User manual

SA850/851 ~
Bi-CompliantTM g
Double Sided ~D
Diskette Storage Drive @
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TABLE OF CONTENTS
.1.0 Theory of Operations . . . . . .. . ........ .
1.1 General Operations.
1.1.1 Head Positioning
1.1.2 Diskette Drive Spindle
....... .
1.1.3 Read/Write Heads
............. .
1.2 Recording
Format. . . ..... .
1.2.1 Bit Cell
.......... . ............ .
1.2.2 Byte
............. .
1.2.3 Recording Format (Double Density) .
1.2.3.1 Rules of Encoding .
1.2.4 Tracks. . . .
..... .
1.2.5 Track Format
............. .
1.2.5.1 Sector Recording Format
1.2.5.2 Soft Sector Recording Format.
1.2.6 Typical Track Index Format
1.2.6.2. . . . . . . . .
..... .
1.3.0 Track Accessing
........ .
1.3.1
................ .
1.3.2 . . . . . . . . . . .
...... .
1.3.2.1. .
............... .
1.3.3 Actuator Control Logic (Figure 21) . . .
........ .
1.3.3.1 Power
On Reset. . ....................... .
1.3.3.2 Forward Seek
.................... . ..... .
1.3.3.3 Reverse Seek
......... . ............... .
1.3.4 Track Zero Indicator. .......... . ............................ .
1.4.0 Read/Write Operations
.......... , ............ . ......... .
1.4.1 . . . . . . . . . . . .. ............... . .......................... .
1.4.2 . . . . . . . . . . . . . .
.. . .................. .
1.4.3 . . . . . . . . . . . ................... .
1
1
1
1
2
3
3
3
4
5
6
6
.......... 6
6
6
. 12
. ........ 13
13
. ........ 13
13
13
. ..... 13
. . 13
14
. ...... 14
.. ........ 17
· .. 17
17
17
1.4.4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
..... 17
1.4.5 . . . . . . . . . . . . . . . . . .
..................................... 17
1.5.0 Read/Write Head . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
1.5.1 .. ....................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .... 19
1.5.2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . ......... 19
1.5.3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.......... 19
1.5.4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
........ 19
1.6.0 Write Current Operation (Figure 32) .............................. . · .. 20
1.6.1 .................. .
1.6.2 . .
............. .
1.6.3
....... .
1.6.4
........... .
1.7.0 Read Circuit Operation (Figure 33)
..
1.7.1 ................. .
1.7.2
............. , ............. .
1.7.3
.......... .
1.8.0
Interface. . .......... .
1.8.1
J1/P1 Connector. . ...... .
1.8.2
AC Power . . . . . . ...... .
1.8.3
DC Power. . ...... .
1.8.4 Output Lines
...
. ......... 20
. ....... 20
. . . . . . . . . . . . . . . . . . . . . . . . . . . 20
.20
. ... 21
. ... 21
. . 21
. .... 21
.22
.22
22
· .. 22
22

2.0 Maintenance Section ............................................................... 25
2.1.0 Maintenance Features .......................................................... 25
2.1.1 Alignment Diskette ............................................................. 25
2.1.2 SA809 Exerciser
........................................... ' .................... 25
2.1.3 Special Tools
................................................................. 25
2.2.0 Diagnostic Techniques .......................................... '.' .............. 25
2.2.1 Introduction .......................................... '.' ...................... 25
2.2.2
"Solt Error" Detection and Correction .............................................. 26
2.2.3 Write Error
................................................................... 26
2.2.4 Read Error
................................................................... 26
2.2.5 Seek Error
.................................................................... 26
2.2.6 Test Points SA850/851
.......................................................... 27
2.2.7 Connectors ................................................................... 27
2.2.7.1 ......... '. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 27
2.2.7.2. . . . . . . . . . . . . . . . . .
.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 28
2.2.7.3 J3/P3
...................................................................... 28
2.2.7.4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.. 29
2.2.7.5 J5/P5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.. 29
2
.. 2.7.6 J6/P6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 29
2
.. 3.0 Preventative Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 29
2
.. 3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 29
2
.. 3.2 Preventive Maintenance Procedures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 29
2
.. 3.3 Cleanliness .... '. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 30
2 .. 3.4 Cautions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 30
2 .. 4.0 Removals, Adjustments ........................................ ; ................ 30
2..4.1 Motor Drive ................................................................... 30
2..4.1.1 Drive Motor Assembly: Removal and Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 30
2..4.1.2 Motor Drive Pulley ............................................................ 30
2..4.2 Head Cover Shield Removal. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 30
2.4.3 Cartridge Guide Access ......................................................... 31
2.4.4 Sectorllndex LED Assembly: Removal and Installation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 31
2.4.5 Write Protect Detector .......................................................... 31
2.4.5.1 Write Protect Detector: Removal and Installation .................................... 31
2.4.5.2 Write Protect DetectorAdjustment ............................................... 31
2.4.6 Head Load Mechanism Assembly .. '.' ............................................. 32
2.4.6.1 Head Load Mechanism: Removal and Installation ................................... 32
2.4.6.2 Head Load Mechanism Adjustment .............................................. 32
2.4.7 Index/Sector Photo Transistor Assembly ............................................ 34
2.4.7.1 Index/Sector Photo Transistor Assembly: Removal and Installation ...................... 34
2.4.7.2 Index/Sector Adjustment .. ' ..................................................... 34
2.4.8 Spindle Assembly .............................................................. 34
2.4.8.1 Clamp Hub Removal .......................................................... 35
2.4.9 Cartridge Guide ............................................................... 35
2.4.9.'1 Cartridge Guide Removal ...................................................... 35
2.4.9.2 Cartridge Guide Adjustment . . . . . . . . . . . . . . . .............................. 35
2.4.10 Head Amplitude Check ......................................................... 36
2.4.10.1 Head Actuator Assembly: Removal and Installation ................................. 36
'2.4.10.2 Head Penetration Adjustment ....... , .......... , ......... , .......... , . , . . 37
2.4.10.3 Head Radial Alignment ........ , , ........... , ....... , ......... , , . . . . . . . . . 43
2.4.10.4 Read/Write Heads Azimuth Check .............. , .......... , .......... ".. 43
2.4.11 Door Lock Solenoid and
In Use LED Assembly Removal .......... , .. , ........ , ........ 44
2.4.12 Track 00 Detector: Removal and Installation .......... , .............. , . . . . .. 46
2.4.12.1 Track 00/76 Stop Adjustment .......... , ........... , ... , ................... , ... 46
2.4.12.2 Track 00 Detector Assembly Adjustment . , .. , .................................... 46
2.4.13 Door Lock Solenoid and
In Use LED Assembly Removal. . . ........... , ........... 46
II

Figure
LIST OF ILLUSTRATIONS
1. SA850/851 Functional Diagram ....... .
2. Bi-Compliant Read/Write Head ........... .
3. Data Pattern .... . ................... .
4. Bit Cell. . . . . . . . . . . .......... .
5. Byte... . . . . . . . .. . ...................... .
6. Data Bytes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . ..... .
7.
8.
9.
FM, MFM and M2FM Encoding ....... .
SA801
Sector Recording Format ..
Track Format ....................... .
MFM Track Format Comparison ...... .
Index Address Mark FM ....................... .
10 Address Mark FM . . . . . . ......... .
Data Address Mark FM . . . . . . ............ .
Deleted
Data Address Mark FM .
MFM Index Address Mark ..................... .
MFM 10 Address Mark ........................ .
MFM Data Address Mark. . . . . . . . . . .................. .
MFM Deleted Data Address Mark. . . ...... .
MFM Index Pre Address Mark ............... .
MFM Pre ID/Data Address Mark . . . . . . . .. . ........ .
Activator Control Logic ......... .
Count 0 . . . . . . . . . . . ................... .
Count 1 ................ .
Count 2 . . . . . . . . . . . .. . ...... .
Count 3 ...... .
Byte .................................. .
Basic R/W Head
Recorded Bit
...... .
Reading a
Bit. . . . ........................ .
1F and 2F Recording Flux and Pulse Relationship
Read/Write
Heads. . . . . . . . . . ...... .
Write Circuit Functional Diagram ........ .
Read
Circuit Functional Diagram
Data Separation Timing Diagram ...... .
Interface Connections.
Interface Signal Driver/Receiver.
Head Load Mechanism Adjustment .......... .
Head Load Timing .
Head Penetration Tools
......... .
Dial Indicator . . . . .................. .
Penetration Plate Installation
Dial
Indicator Installation ...... .
Installation Check .......... .
2
2
3
.. .. 3
4
4
5
6
7
8
8
9
9
9
· .. 10
·
....... 10
·
.. 10
· . 11
.. ..... 11
. ....... 11
· .. 15
· .. 16
.
............. 16
. . . . . . . .
.. 16
· . 16
. ............... 17
. ...... 18
.
.......... 18
· . 18
· . 19
· ....... 19
. .... 20
·
.. 21
. ... 22
· .23
· .. 24
· ....... 33
.33
· ....... 37
· .38
. ......... 39
· . 40
. ... 41
· ....... 41
. ............. 42
10.
11 .
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
2·3.
24.
25.
26.
27.
28.
29.
30.
31.
32.
33.
34.
35.
36.
37.
38.
39.
40.
41.
42.
43.
44.
45.
46.
47.
Correct Penetration.
Penetration Adjustment.
Head Radial Alignment
Motor Plate . . . . . . . . . . . . . 44
. . . . . . . . . . . . . . 44
III

48. Azimuth Burst Patterns ....................................................... 45
FlowCharts ........................ . ......................................... 47
logic Diagrams : .................... " ..... " ..................................... 53
Physical Locations ........... : . . . . . .. . ........................ ' ................. 57
49.
(1 of 2) .................................................................... 61
49. (2 of 2) ........... " .............. " .......................................... 62
Illustrated Parts Catalog ........... " ... " .......................................... 63
50.. " .......................... " ... " .......................................... 64
51 ...................... " .......... "" .............................. " " ......... 67
Schematic Diagrams
................. " .......................................... 68
IV

1.0 THEORY OF OPERATIONS
1.1 GENERAL OPERATIONS
The SA850/851 Diskette Drive consists of read/write and control electronics, drive mechanism, read/write
heads, track positioning mechanism, and removable Diskette. These components perform the following
functions:
• Interpret and generate control signals.
• Move read/write heads to the desired track.
• Read and write data.
The relationship and interface signals for the internal functions of the SA850/851 are shown
in Figure 1.
The Head Positioning Actuator positions the read/write heads to the desired track on the Diskette. The Head
Load Actuator loads the read/write heads against the Diskette and data may then be recorded or read from
the Diskette.
The electronics are packaged
on the PCB. The PCB contains:
1. Index Detector Circuits (Sector/lndex for SA851).
2. Head Position Actuator Driver
3. Head Load Solenoid Driver
4. Read/Write Amplifier and Transition Detector.
5. Data/Clock Separation Circuits (SA851).
6. Write Protect
7. Drive Ready Detector Circuit.
8. Drive Select Circuits.
9. Side Select Circuit.
10. In Use and Door Lock Circuits
11. Write Current Switching/Read Compensation
1.1.1 HEAD POSITIONING
The read/write heads are accurately positioned by a Fasflex™ metal band/stepping motor actuator system.
A precision stepping motor
is used to precisely position the head/carriage assembly through the use of a uni-
que metal band/capstan concept. Each 3.60 rotation of the stepping motor moves the read/write head one
track in discrete increments.
1.1.2 DISKETTE DRIVE SPINDLE
The Diskette drive motor rotates the spindle at 360 rpm through a belt-drive system. 50 or 60 Hz power is ac-
commodated by changing the drive pulley and belt. A registration hub, centered
on the face of the spindle,
pOSitions the Diskette. A clamp that moves in conjunction with the latch handles fixes the Diskette to the
registration hub.

1.1 .. 3 READ/WRITE HEADS
READ
LOGIC
WRITE
LOGIC
SIDE
READ DATA
SEP DATA (FMI
SEP CLOCK (FMI
WRITE CURRENT
WRITE DATA
WRITE GATE
WRITE PROTECT
SELECT POWER ON RESET
INDEX DETECTOR
INDEX LED
STEPPER ... A
STEPPER -A
,·B
STEPPER -8
CONTROL
LOGIC
t
FIGURE 1. SA850/851 FUNCTIONAL DIAGRAM
SIDE SELECT
IN USE LED
HEAD LOAD (OPTIONAL!
STEP
DIRECTION/SIDE SELECT (OPTIONAL!
DRIVE SELECT
TRACK 00
INDEX
READY
SECTOR (851)
ALTERNATE I/O (3 LINES)
TWO SIDED
(OPTIONAl)
DISK CHANGE
The proprietary heads are a single element ceramic read/write head with straddle erase elements to provide
erased areas between data tracks. Thus normal interchange tolerances between media and drives will not
degrade the signal to noise ratio and insures diskette interchangeability.
The read/write heads are mounted on a carriage which is pOSitioned by the Fasflex™ actuator. The head
carriage assembly utilizes a combination flexured/rigid head mounting system. This allows the flexured head
to load the media against its rigidly mounted counterpart (see Figure
2).
The diskette is held in a plane perpendicular to the read/write head by a platen located on the base casting.
This precise registration assures
perfect compliance with the read/write heads. The read/write heads are in
direct contact with the diskette. The head surface has been deSigned to obtain maximum signal trans·fer to
and from the magnetic surface of the diskette.
FIGURE 2. BI-COMPLIANT READ/WRITE HEAD
2

1.2 RECORDING FORMAT
The format of the data recorded on the Diskette is totally a function of the host system. Data is recorded on
the diskette using frequency modulation as the recording mode, i.e., each data bit recorded on the diskette
has an associated
clock bit recorded with it, this is referred to as FM encoding. Data written on and read
back from the diskettes takes the form as shown
in Figure 3. The binary data pattern shown represents a
101.
1.2.1 BIT CELL
As shown in Figure 4, the clock bits and data bits (if present) are interleaved. By definition, a Bit Cell is the
period between the leading edge
of one clock bit and the leading edge of the next clock bit.
1.2.2 BYTE
CLOCK BITS
~BIT CELL----1
FIGURE 3. DATA PATIERN
~ ... B_IT_S __ .... ~
i
DATA BITS
FIGURE 4. BIT CELL
A Byte, when referring to serial data (being written onto or read from the disk drive), is defined as eight
(8)
consecutive bit cells. The most Significant bit cell is defined as bit celiO and the least significant bit cell is
defined as bit cell
7. When reference is made to a specific data bit (i.e., data bit 3), it is with repsect to the
corresponding bit cell (bit cell
3).
During a write operation, bit celiO of each byte is transferred to the disk drive first with bit cell 7 being
transferred last. Correspondingly, the most significant byte
of. data is transferred to the disk first and the
least significant byte is transferred last.
When data is being read back from the drive, bit celiO of each byte will be transferred first with bit cell 7 last.
As with reading, the most significant byte will be transferred last from the drive to the user.
Figure 4 illustrates the relationship of the bits within a byte and Figure 6 illustrates the relationship of the
bytes for read and
write data.
3

C C o
BITCELL 0
USB
-----------------------B~-----------------------
BINARY REPRESENTATION OF:
DATA BITS
CLOCK BITS
HEXADECIMAL
REPRESENTATION
OF
DATA BITS
CLOCK BITS
t
BIT CELL 0 OF BYTE 0 IS
FIIRST DATA TO BE SENT
TO THE DRIVE WHEN
WIfIITING AND FROM THE
Df~IVE WHEN READING
o o
FIGURE 5. BYTE
FIGURE 6. DATA BYTES
1.2.3 RECORDING FORMAT (DOUBLE DENSITy)
.0
CDC
t
BIT CELL 7 OF BYTE 17 IS
LAST DATA TO
BE SEIH TO
THE DRIVE WHEN WAITING
AND FROM THE DRIVIE
WHEN READING
Double capacity can be obtained by use of MFM (modified frequency modulation) and M2FM (modified,
modified frequency modulation) rather than
FM (frequency modulation) which is the standard method of en-
coding data on the diskette.
The differences between FM, MFM and M2FM encoding are shown in Figure 7. Note that MFM and M2FM
result in a 1 to 1 relationship between the "flux changes per inch" and the bits per inch recorded Oln the
diskette. This also results
in a doubling of the data transfer rate, from 250 to 500 KBS, when compared to
FM ..
Data error rate performance equal to standard capacity diskettes using FM encoding can be achieved by us-
ing:
• The SA850/851 diskette drive with its proprietary ceramic/ferrite read/write head.
• Phase locked loop (VFO) data separator
• Write precompensation.
Provision
of the phase locked loop data separator and write precompensation circuitry is the responslibility
of the user of the SA850/851 diskette drive.
Shugart Associates will provide design information, as required, to SA850/851 users who desire to incor-
porate double capacity diskette drives in their products.
The bit cell for MFM and M2FM encoded data is one half the duration of the bit cell for FM encoded data.
Also, unlike FM, and MFM and M2FM bit cell does not always contain a clock bit at its leading edge. This lack
of clock bit makes data separation more complex Also, the window size is half the FM window size, which
results in less tolerance to bit shift. The only reliable method to separate MFM and M2FM encoded data is
through use of a phase locked loop (VFO) type
of data separator. The VFO, once synchronized, tracks the
data and generates clock and data windows, improving the bit shift tolerance over the conventional
"hard"
data separators commonly used in FM recording, which use windows of fixed timing.
4

1.2.3.1 RULES OF ENCODING
FM Encoding:
• Write data bits at the center of the bit cell.
• Write clock bits at the leading edge of the bit cell.
MFM Encoding:
• Write data bits at the center of the bit cell.
• Write clock bits at the leading edge of the bit cell if:
1) There is no data bit written in the previous bit cell, and
2) There will be no data bit written in the present bit cell.
M2FM Encoding:
• Write data bits at the center of the bit cell.
• Write clock bits at the leading edge of the bit cell
if:
1) There is no data bit or clock bit written in the previous bit cell, and
2) There will be not data bit written in the present bit cell.
NOTE: In M2FM/MFM, the write oscillator frequency is doubled, while maintaining the same flux changes per
inch
as FM. Thus, the bit cell in M2FM/MFM is V2 that in FM. Data transfer rate is also doubled, since a
1 to 1 relationship exists between flux changes per inch and bits per inch
(2 to 1 in FM).
BIT I
CELLS~ ______ ~ ____ ~ ______ ~ __ O __ ~~ ____ ~ __ O ____ ~ __ O __ ~ ___ O __ -L ____ ~
FM
I
1
121
1
I
ID D D
11
D
~~LLS ____ 1 .... 1_1 .... 1_1 ......... 1 _0 .L..I _1 .... 1_° ..... 1_° .......... 1 _0 .... 1---,
D D D D
MFM
D D D D D
~I 4/31 ~
11 H 4/51
,
,
,
,
,
, ,
~
, ,
~
FIGURE 7. FM. MFM AND M2FM ENCODING
5
,
,
,
,
,
,
,
,
,
~
, , ,
,
~
,