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LOGIC CHASSIS ASSEMBLY
The logic chassis assembly consists of a
wil:e
wrap board, logic cards, Maintenance panel,
air plenum and dc power supply.
The entire
assembly forms the rear door to the cabinet.
Flexible tubing from the blower assembly
connects to the air plenum and provides air
to cool the logic cards and the dc power
supply.
The logic cards are installed on the pro-
truding pins of one side of the wire wrap
board.
Wiring between cards and to and from
the logic chassis occurs at the protruding
pins on the opposite side of the wire wrap
board.
Access to this wiring is gained by
releasing two 1/4-turn fasteners at the top
of the door and removing the outer surface
of the rear door.
The logic card section contains the bulk of
the logic cards used in the cabinet (five
cards are located on the deck assembly).
The vertically mounted cards are installed
in four rows (A top row and D bottom row)
at numerically identified locations.
Some cards span two rows and are referred to
as full-size cards.
Others span a single
row and are called half-size cards.
Refer
to the Diagrams section of the Maintenance
manual for a description of the logical
functions performed by the cards.
The Logic
Card manual provides a physical description
of the cards.
The Wire Lists section of the
Maintenance manual contains a tabulation of
the wire wrap connections made in the
~.
The test point panel at the top of the logic
chassis provides a convenient point to
~
the dc voltages.
At the bottom of the logic
chassis assembly, and on the front panel of
the dc voltage section of the power supply,
are located the LOCAL/REMOTE switch, the
indicator for +20Y power and the circuit
breakers for ±46v, ±20v, and ±lOv.
Specific
information on each control or indicator on
the test point and dc power panel is pro-
vided in the Operation section of this
~.
ME Maintenance panel contains a set of test
point jacks, switches and indicators that
relate to the operational status of the drive.
These components function primarily in the
maintenance mode as a troubleshooting aid.
Specific information on each control or in-
dicator is provided in Section 2 of this
manual.
DECK ASSEMBLY
GENERAL
The deck assembly mechanism (Figure 3-6)
drives the disk pack and loads and pOSitions
the read/write and servo heads.
The deck
assembly consists of a drive motor, hyster-
esis brake, spindle, actuator, two trans-
ducers, and a first seek interlock assembly.
83318200
A
DRIVE MOTOR
The drive motor drives the spindle assembly.
The motor is a 3/4-hp unit of the induction
type.
The motor is secured to a mounting
plate.
The motor mounting plate is secured
to the underside of the deck plate in such
a manner as to allow control of belt tension.
Power is transferred to the spindle via a
flat, smooth-surfaced belt that threads over
the pulleys of the spindle and drive motor.
Two
idler springs maintain a constant ten-
sion on the motor mounting plate to keep the
belt tight.
A second pulley on the drive motor shaft
links the motor (via a V-belt) to the hys-
teresis brake.
The temperature of the drive motor is moni-
tored by an internal thermostat.
If the
motor overheats, the thermostat opens.
This
applies ac across the DRIVE MOTOR circuit
breaker coil to open the contacts.
The re-
sult is a speed loss (refer to Power Sup-
plies).
The DRIVE MOTOR circuit breaker
must be reset to ON to restore operation.
HYSTERESIS BRAKE
The hysteresis brake decelerates the drive
motor during a Power-off sequence (refer to
Power-off sequence paragraph).
The brake
is energized whenever Motor relay K3 is de-
energized.
The brake mounts on a plate
which, in turn, is mounted on the motor
mounting plate.
The brake and motor shafts
are linked via a V-belt and a pulley on each
shaft.
The brake consists of two concentric perme-
able bodies.
These cylinders are assembled,
one inside the other, with a uniform gap
separating the outer diameter of one from
the inner diameter of the other.
These
adjacent surfaces are machined to contain
a series of pole faces.
A permanent magnet,
in the shape of a cup, fits in the gap to
separate the cylinders.
This cup is con-
nected to the brake shaft.
As long as
spindle motor power is applied, brake power
is not available and the cup is driven at
the speed of· the motor.
When spindle motor
power is removed, braking power is applied.
A flux field is created between the inner
and outer cylinder pole faces as braking
voltage (+20 volts) is applied to the inner
cylinder.
The flux field sets up what -'is in
effect magnetic friction between the inner
cylinder and the cup, causing the cup (and
brake shaft) to decelerate.
Brake deceler-
ation in turn causes spindle motor deceler-
ation.
3-11
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