Sansui SR 7090 Service Manual

Page 1

1. BLOCK DIAGRAM

1) SR-737/SR-7090
Fig. 1-1 If" l
I MOTOR :
I
I ' FG SERVO CIRCUIT
I l r' --------- - " I I - - " - 'l
I SPEED ' ' SPEED PROPO- 53E AJGEENCY VOLTAGE I CONTROL '
I SENSER I I TIDIIAL PULSE CONVERTER COMPARATOR I I CIRCUIT :
I. _______ .I I. _ _ _. ______________ - _. J I I
_ _ _ _CB. ELL _S.E_BILO.CBQULT_ _I I I
{- I I ELECTRONIC I
1/4 DEMULTIPLI- PHASE I BRAKE I
I CATION COMPARATOR L _ J
I I -----
' I
' I
: CR GENERATOR :
L. _______________ J
IOTDR CONTROL CIRCUIT
Fig. 1-2 ." """""""""""""""""""""""""""""" I Ls-I--Ls-3 POSIIIDN SENSEPCOIL
I T'- 5 IBM; LSHC-g ORIva COIL
' - - - - I -.; IA IL
I 3 3 3 3 3 s : '
FG SERVO CIRCUIT 5 i I
. E i E
0 I I I
,- E i E
LEONE E I I L. ..... Ina:
's'p'E'EEI' TRANSISTOR I "1' I
SENSIR ......................................... .I
i I ..
I PLI. Hrs; ' r
5 83:50? 0 DIVIDER AND PIIAsE COTTPARATDRITTSTTSDIO)
. M , . V-
'I , ............... EEEEESEBIDEDchiC: ii: ............. I

oy.v

CR GENERATOR
FREQUENCY I D J

SST/1:869 PHASE COMPARAIO
5 OUIPUI ADJ m
SJIII'OII I
M 45.90:; 5

PLL SPEED SELECTOR SW J

L ......................................................

SR-737, SR-7090 Main Circuit

The electronic circuitry in this set is two servo circuits and a motor

control circuit.

This set employs both the F-G servo system and PLL servo system

by which rotation fluctuation is always locked in the reference
The servo circuit employs the PLL servo system and the speed signal.
control system (frequency-generator servo) together.

Page 2

2) SR-535/SR-509O

Proportional voltage
by motor rotation

Reference Voltage
voltage comparator
009

007

Generator Coils
Ln-1 , Ln-2, Ln-3

Befilar windings

Drivin Coils
Lm-1,-,ng2 Lin-3

001, 04
002. 05
003. w

Switching
circuit

Current si nal
generated y
position sensor

Position
Sensor

2. OPERATIONS 0F ELECTRIC CIRCUIT

A.SR-535/SR-5090

D.D. Motor of this direct-drive player system is DC blushless servo
motor having 20-pole on interior surface of the rotor magnet and
30 slots for winding stator coils, which ensure the performance
for extremely less wow-flutter and overload fluctuation. Namely,
driving operations of this 0.0. Motor connected with V.G (Voltage
Generator) servo circuit board are as follows.

Generator coils, Ln-i , Ln-2 and Ln-3 oscillate voltage pr0portiona|
by rotation speed of the motor. Voltage comparator compares the
voltage induced by rotation speed with reference voltage,5.l volts,
from printed circuit board, 5-0015. Control circuit, 008, restricts
current of driving coils by control signal occurred in the voltage
comparator, 009.

When this current flows by turn into one of three driving coils,
Lm-l, Lm-2 and Lm-3, the motor rotation speed varies to the
current proportionally. And, the induced voltage of three genera-
tor coils change proportionally by changing motor rotation speed.
ln other words, voltage comparator compares the voltage propor-
tional by rotation speed induced in generator coils with reference
voltage, 5.1 V,asa result, control voltage appears at one of collec-
tors of 009.This control voltage is provided for the purpose of
obtaining an accurate rotation speed of the motor free from load-
fluctuation of motor revolution.

As mentioned above, the motor is blushless outer rotor motor and
this outer rotor on interior surface is magnetized in order of
N-S-N-S poles regularly. The induced current by the rotor-turn
flows into one of driving coils. Namely, very weak high-frequency
signal, 83 kHz generated by oscillator coil, LOi, and capacitor,
CO7, adds to three position sensors. This sensor detects the turning
angle of rotor, and it generates current signal corresponding to
rotation angle which operates for switching circuits, 001, 002,
003, 004, 005 & 006, then it flows into Lm-l , Lm-2 and Lm-3
by turn, resultly, the current drives turntable (platter) to obtain
an accurate normal speed rotation.

Voltage Comparator

® iReference voltage 5.1 V

IProportional voltage
from generator coils
by rotatoin speed of
motor

© : Control voltage