Sony DVW-A500P Maintenance Manual page 111

[CIRCUIT DESCRIPTION OF DR-307 BOARD]
DR-307 board is a servo driver board that drives the
mechanical devices of each mechanical block under the
control from a servo control block (on SS-52 board (2/3)),
receives various sensor and FG signals, and feeds them
back to the servo control block. DR-307 board also mounts
the REC/PB amplifier of a CTL signal.
The configuration of DR-307 board is summarized as
described below.
. Four-bit MPU (IC106) that exchanges data and commands
with the servo CPU on SS-52 board (2/3) by serial commu-
nication.
. Four switching drivers that drive the motors (drum,
capstan, and supply and take-up reel motors) in the tape
transport system.
. Three two-way switch drivers that drive the motors
(loading, position, and cassette compartment up/down
motors) in the loading system.
. Five drive amplifiers that drive the solenoids (pinch,
supply and take-up reel brake, and cleaning solenoids)
and CC lamp.
. Wave shaping amplifiers of each FG pulse (drum,
capstan, supply and take-up reel, and loading FGs).
. Detection amplifiers of tape tensions (supply and take-up
tensions).
. Detection amplifier of tape ends (tape top and end).
. CTL signal REC/PB amplifier.
A complementary explanation is given for the contents of
the above description.
(1) Servo driver MPU
The serial data from the servo CPU on SS-52 board is
converted into parallel data by this MPU (IC106) and sent
to each block on DR-307 board. This data is partially used
to drive the solenoids via drive amplifiers. The signal that is
fed back from each sensor is sent to this MPU as parallel
data, converted into serial data, and sent to the servo CPU
on SS-52 board.
An EEPROMs (IC101) save the servo- and DT-related
adjustment data.
(2) Tape transport system motor drive
The drum motor, capstan motor, supply reel motor, and
take-up reel motor that constitute the tape transport system
require a high-precision control. Therefore, motor drivers
for these motors receive the control signals that are sent
from SS-52 board by PWM signals and perform the analog
drive control by switching drivers.
That is, the chopper type switching regulator (drive voltage
generator circuit) that uses a PWM power controller IC
converts the voltage of +18 V supplied from the power
supply block into the voltage proportional to the control
signal from SS-52 board to control the motor speed.
Take the case of the drum motor driver so as to describe
the theory of the switching regulator. The "DRUM PWM"
control signal from SS-52 board is sent to a low-pass filter
to produce a DC signal and compared with the voltage that
is fed back from the output side of the regulator in the input
DVW-A500P/500P
stage of an operational amplifier (IC112). As the result, a
PWM pulse whose pulse width varies depending on the
difference voltage (error voltage) is output from IC112. This
pulse drives the gate of a switching FET (Q110) via IC8.
When Q110 is OFF, the current flows continuously through
a flywheel diode (D104) into the inductor to charge the
capacitor, by the current energy holding effect of inductor.
The balanced output voltage value varies with the modula-
tion ratio of a PWM pulse and the capacity of an output
current. However, the modulation ratio of the PWM pulse is
controlled so that the output voltage becomes a control
target value by feeding an output voltage back to IC112.
The basic operation of the switching regulator is as de-
scribed above. Since the drum motor is a three-phase
brushless motor, a three-phase switching circuit that
supplies a current to each winding according to the three-
phase control signal (output signal of Hall device amplifier)
from the drum is provided after the switching regulator.
The capstan motor incorporates a three-phase switching
circuit. The rotating direction of the capstan motor is
directly switched by the "CAPSTAN MOTOR DIR" signal
that is sent from SS-52 board via DR-307 board. There-
fore, the capstan motor operates by only sending a drive
voltage from DR-307 board.
The switching regulator uses an output current detection
voltage for a fed back voltage and functions as a current
control type regulator.
The reel motor driver is a dual switching regulator in which
switching regulators are connected to both terminals of a
DC motor. This reel motor driver feeds back the detection
voltage of an output current occurring due to the voltage
difference at both terminals to control each output voltage.
In each switching converter that constitutes this regulator, a
switching FET that makes a complementary pair with a
drive switching FET is used instead of the flywheel diode.
(3) Loading system motor driver
For the motors in the loarding system, there are a loarding
motor (threading motor), position motor (reel shift motor),
and cassette compatment motor (up/down motor). These
motor are DC motors and are driven by two-way switch
driver ICs. This IC can select four states (forward rotation,
reverse rotation, short-brake, and open) by two control
lines.
The switching converter controlled by the "LOADING PWM"
pulse from SS-52 board is used in the driver power source
for the loading motor, so can also control the rotation torque
of the loarding motor.
3-63 (b) 3-59
DR-307 DR-307
3-63 (b) 3-59