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Preamplifier Board; Motor Control Board; Device Electronics Board; Read/write Functional Description - HP 7957A Hardware Manual

Hp disc drives hardware support manual.
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of the base, along with the brake mechanism.
Switching information for the electronic com-
mutator is supplied by three Hall-effect sensors
positioned within the motor assembly.
3-15.
PREAMPLIFIER BOARD
Electrical connection to the heads and the
positioner is made via flexible circuits which pass
through a port in the HDA casting. The port is
sealed with a gasket to maintain the integrity of
the clean area. The flexible circuits then connect
to the Preamplifier board mounted on the HDA
casting. The Preamplifier board contains the The
servo signal preamplifier IC and the read/write
preamplifier IC.
The read/write preamplifer IC
contains the read signal preamplifier circuits, head
select circuits and write current drivers.
• Head selection (for up to eight data heads).
• Read signal preamplification.
• Servo signal preamplification.
• Write fault detection.
3-16.
MOTOR CONTROL BOARD
The electronic components associated with the DC
Motor and with the servo power amplifier circuit
for the positioner are mounted on the Motor
Control board. The board provides the following
functions:
• Spindle motor commutation, current limiting,
and control.
• Positioner signal power amplification.
• Brake solenoid control.
• DC power filtering and reference voltage
generator.
Theory Of Operation
7957/7958
3-17.
DEVICE ELECTRONICS BOARD
The remaining electronic components are mounted
on the Device Electronics board, which provides
the overall control functions for the drive. The
board contains microprocessor-based control logic
and interface drivers and receivers. The board
provides the following functions:
• Power-up and power-down sequencing.
• Spindle speed control to
±O.5
percent accuracy.
• Servo
signal
amplification,
AGC,
and
demodulation.
• Closed loop positioner servo.
• Velocity profile generation.
• Read channel signal processing.
• Fa ult detection.
• Index, Guardband, and Track 0 decoding.
• Write data encoding.
• Data separation and read data decoding.
• Index and sector pulse generation.
3-18.
3-19.
READ/WRITE FUNCTIONAL
DESCRIPTION
WRITE CHANNEL
When the drive is selected and in the write mode,
data to be written is received over the drive inter-
face via balanced, differential data lines NRZ
WRITE DATA± with timing provided by the
Write Clock signa1. Write data is transmitted from
the controller to the drive as a serial binary data
stream with a clock signal. Data is encoded (from
NRZ data to 2,7 RLL data), and then applied to
the Read/Write Head Select circuit. A flip-flop, in-
ternal to the control circuit, is clocked by the data
pulses. Each time the flip-flop changes state, the
write drivers in the control circuit switch the head
3-9

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