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Theory of Operation
DRIVE FAULT LAMP
DRIVE READY LAMP
LATCH DRIVE
LOAD SWITCH
TACH IN
ACHANNEL
ECT
B CHANNEL
C CHANNEL
DATA PROTECT
."
."
.,
,
., ,.
."
SEEK HOME
...
CURRENT COMMAND
....
-
~
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SERVO INHIBIT
....
~
VELOCITY COMMAND
ENERGIZE SERVO READY
--..
----
AT HOME
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' - -
RETRACT SWITCH CLOSED
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ENCODER
' . .oir
CARRY
...
SERVO/
~
ASSEMBLY
~
CYLINDER MATCH
....
AMPLI FIER/
....
HEADS LOADED
A9
REGULATOR
-
.....
~
FORWARD COUNT
ASSEMBL Y
....
POSITION MATCH
REGU LATED
¥.;
VDC
~}
.....
+8VDC
---..
A4
r
TO
...
RETRACT
....
VELOCITY
LINEAR
CARRIAGE
HEAD POSITION
HEADS
DISC
.....
....
REVERSE COUNT
FROM {
+20 VDC --..
REGULATED +12 VDC ---..
DISC DRIVE
TRANSDUCER
MOTOR
I
ENCODER
/
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~
....
POWER
REGULATED -12 VDC:
LOGIC
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7
MB
"
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SUPPLY
-20VDC
...
lUTBUS 7
....
....
ENERGIZE SERVO RELAY
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....
DRIVE
CONTROL
ENERGIZE MOTOR RELAY
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\ \ \ I
ASSEMBLY
....
A10
INITIAL RESET
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~
I
'\
RESET COUNTERS
..
~
RETRACT
."
J
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1/
~
I
.....
SPEED DOWN
SWITCH
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I
r----
0~
HUB SKIRT
.....
S8
\ \ \ \ I
I
I~
....
CARRIAGE RETRACTED
....
,.,.
~
-I
I
I
...............
-=
'10TE1)
....
....
SPEED UP
.....
...
~
...
~
SPINDLE
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...
MOTOR
LOCK
..
....
-"
....
....
ILLEGAL ADDRESS
---+
SECTOR
....
TRANSDUCER
...
~
....
R/W UNSAFE
HEAD 1 SELECT
....
A, B & C CHANNEL
ASSEMBLY
....
"' "
.....
R/W RESET
. .
HEAD 0 SELECT
...
,
A2
....
"' "
.....
HEAD 1 WRITE, ERASE, READ CURRENT
.....
ACCESS READY
....
WRITE A
---..
....
HEAD 0 WRITE, ERASE, READ CURRENT
"' "
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~
SELECT AND CONTROL
...
WRITE B
. .
....
:
....
SECTOR TRANSDUCER
SEEK
...
WRITE GATE
WRITE DRIVER/
~
"' "
....
READ
DECREASE WRITE CURRENT
..
PREAMPLIFIER
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ASSEMBLY
SEE NOTE 4)
4
..... REVERSE COUNT
ERASE GATE
---..
A6
.....
READ/WRITE
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120 VAC
. .
.,,,,.FORWARD COUNT
CONTROL
....
READA
MOTOR CONTROL
~
r'
... CYLINDER MATCH
ASSEMBLY
.:
ENERGIZE MOTOR RELAY
....
ASSEMBLY
CARD CAGE
A7
READ B
"' "
120 VAC
...
FAN MOTOR
....
A3
CARi'iY
...
AC WRITE DETECT
r'
.....
SECTOR/CYLINDER
VELOCITY COMMAND
....
DC WRITE DETECT
SEEK
ASSEMBLY
~
ERASE DETECT
..
All
....
r'
.....
DRIVE SET HEAD AND SECTOR
...
HEAD 1
...
....
MULTI-HEAD DETECT
"' "
r"
....
SECTOR COMPARE
HEAD 1
---..
SECTOR PULSE
>
TRACK 128
:
....
NOTES:
DRIVE OUTBUS 0 THRU 7 (8 LINES)
_
..
.....
. .
I
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.....
,
1.
THE "NOT" INTERLOCK LINE IS ACTIVE WHEN THE FOLLOWING CONDITIONS ARE SATISFIED:
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a.
A CARTRIDGE IS PROPERLY INSTALLED
DRIVE OUT BUS 0 THRU 4 LINES (5 LINES)
b. THE DISC DRIVE DOOR IS CLOSED AND LATCHED
c.
PRINTED CIRCUIT ASSEMBLIES A6 THRU A 12 ARE PROPERLY INSTALLED IN MOTHERBOARD A5
......___READ DATA
2.
THE ENCODER LAMP INTERLOCK IS ACTIVE WHEN THE ENCODER LAMP HAS CURRENT.
PAIR
SECTOR TRANSDUCER
....
3 .
SIGNAL FLOW FROM THE DISC DRIVE TO THE DISC SERVICE UNIT NOT ILLUSTRATED.
,
4. SWITCH S31LLUSTRATED IN THE OVERRIDE POSITION.
Figure 4-3. HP 7901 Disc Drive, Block Diagram
4-11/4-12
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