Sony DVW-A500P Maintenance Manual page 115
Digital videocassette recorder
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Also See for DVW-A500P:
- Maintenance manual (524 pages) ,
- Manuel de fonctionnement (164 pages) ,
- User manual (157 pages)
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[CIRCUIT DESCRIPTION OF DR-200 BOARD]
DR-200 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-200 board also mounts
the REC/PB amplifier of a CTL signal.
The configuration of DR-200 board is summarized as
described below.
. Four-bit MPU (IC3) 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 (IC3) and sent to
each block on DR-200 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.
Two EEPROMs (IC10 and IC25) save the servo- and DT-
related adjustment data under the same contents and back
up it mutually.
(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
(IC39) to produce a DC signal and compared with the
voltage that is fed back from the output side of the regulator
in the input stage of a PWM power controller (IC700). As
DVW-A500P/500P
the result, a PWM pulse whose pulse width varies depend-
ing on the difference voltage (error voltage) is output from
IC700. This pulse drives the gate of a switching FET
(Q106) via IC8. When Q106 is OFF, the current flows
continuously through a flywheel diode (D102) into the
inductor to charge the capacitor, by the current energy
holding effect of inductor. The balanced output voltage
value varies with the modulation 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 IC700.
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-200 board. There-
fore, the capstan motor operates by only sending a drive
voltage from DR-200 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.
The PWM power controller outputs an in-phase PWM pulse
from pins 8 and 11, fluctuates the voltages at both terminals
in the opposite directon according to the duty cycle ratio of
the PWM pulse, and drives the motor differentially. 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 (a)
3-63
DR-200
DR-200
3-63 (a)
3-63
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