Servo Circuits - Kenwood DP-1100 B Service Manual

DP-11D0BI I

1-2 Servo circuits

1-2-1 F o c u s s e r v o circuit
T h e f o c u s error (FE) s i g n a l , g e n e r a t e d in t h e m e c h a n i s m PCB,
is f e d into pin 8 of C N 6 o n t h e servo PCB, T h i s signal is used
in m a k i n g signal DOK w h i c h t h e p r e s e n c e or a b s e n c e of t h e
disc is j u d g e d w h e n t h e tray is c l o s e d .
W i t h a disc present, " L " signal DOK is o u t p u t f r o m pin 1 of
C N 2 t o pin 2 7 of IC15 o n t h e p r o c e s s PCB ( X 3 2 ) .
On t h e o t h e r h a n d , w h e n t h e RF signal f r o m the p i c k u p is i n ­
p u t t o pin 2 0 of I C 1 5 , pin 1 2 (FOK) of IC16 is at - 1 2 V a n d
Q 2 t u r n s OFF. Signal FE t h r o u g h f o c u s gain
p o t e n t i o m e t e r V R 1 is a m p l i f i e d in IC1 ( 1 / 2 ) a n d i n p u t t o IC2
( 1 / 2 ) via t h e phase c o r r e c t i o n CR c i r c u i t . T h e n , t h e signal
p o w e r - a m p l i f i e d in IC2 ( 1 / 2 ) drives t h e p i c k u p a c t u a t o r coil t o
f o r m a servo l o o p i n c l u d i n g t h e optical p i c k u p by w h i c h the
laser b e a m is a l w a y s f o c u s e d exactly o n t h e disc pit surface ir­
respective of t h e a m o u n t of disc w a r p , e t c .
D u r i n g light e m i s s i o n of t h e laser d i o d e , the gate of FET Q 4
c o n n e c t e d t o t h e LDC line is " L " so t h a t IC2 ( 1 / 2 ) p e r f o r m s
n o r m a l a m p l i f i c a t i o n . In a d d i t i o n , t h e gate of Q6 c o n n e c t e d t o
t h e FOK line is at — 1 2 V w h e n
T h e r e f o r e , Q 6 t u r n s OFF a n d a m p l i f i c a t i o n is possible in the
l o o p c o n n e c t i n g IC1 a n d I C 2 , w h e r e t h e f o c u s servo w o r k s .
1 - 2 - 2 T r a c k i n g s e r v o circuit
Signals S1 (A + B) a n d S2 (C + D ) , p r o d u c e d by t h e pre­
a m p l i f i e r o n t h e m e c h a n i s m PCB, are f e d into pins 6 a n d 7 of
c o n n e c t o r C N 6 . These signals are partially a m p l i f i e d by a
3-stage a m p l i f i e r of inverter IC5 t o g e n e r a t e the t r a c k i n g error
s i g n a l , t h e n w a v e f o r m - s h a p e d by IC7 a n d i n p u t t o TS1 a n d
T S 2 of I C 1 5 .
T h e t r a c k i n g error signal is g e n e r a t e d in IC15 a n d o u t p u t f r o m
TEOP a n d T E O N . T h i s signal w o r k s as the t r a c k i n g servo
s i g n a l .
On t h e o t h e r h a n d , signals S1 a n d S2 are c o m b i n e d via R 1 0 0
a n d R 1 0 1 t o e x t r a c t m u s i c signal. T h e c o m b i n e d signal is i n ­
p u t t o IC6 w h i c h acts as an amplifier like IC5. After 1 st stage-
a m p l i f i c a t i o n , it is f u r t h e r 2-stage a m p l i f i e d t h r o u g h t h e EFM
test p o i n t via t h e s e c o n d - s t a g e
c o n t r o l l e d by DSV a n d is i n p u t t o pin 17 (EFM I) of I C 1 5 .
T h e t r a c k i n g error signals o u t p u t f r o m pins 3 a n d 4 of IC15
(TEOP a n d TEON) are c o m b i n e d in IC12 ( 1 / 2 ) . T h e c o m b i n e d
o u t p u t (TE) is p h a s e - i n v e r t e d in I C 1 4 ( 1 / 2 ) a n d i n p u t via
t r a c k i n g g a i n t r i m m i n g p o t e n t i o m e t e r V R 2 t o pin 6 of IC1
( 2 / 2 ) in w h i c h it is p h a s e - c o r r e c t e d a n d a m p l i f i e d .
Further, o u t p u t of IC1 ( 2 / 2 ) is p o w e r - a m p l i f i e d in IC2 ( 2 / 2 ) ,
Q 1 0 a n d Q 1 1 . A m p l i f i e d TE signal drives t h e p i c k u p a c t u a t o r
coil t o f o r m a t r a c k i n g servo by w h i c h t h e laser b e a m s p o t
f o l l o w s e x a c t l y t h e pit s e q u e n c e o n t h e disc.
34
1. CIRCUIT DESCRIPTION
a d j u s t m e n t
RF signal is p r o v i d e d .
amplifier w h i c h is bias-
1 - 2 - 3 D S V circuit ( I C 8 ( 1 / 2 ) a n d I C 1 5 D L S 1 a n d 2)
Pits are m a d e o n a disc in s u c h a w a y t h a t the s u m of " H "
d u r a t i o n s is equal t o t h a t of " L " d u r a t i o n s i.e. DSV (Digital
S u m Value) is z e r o . T h u s , this c i r c u i t c o n t r o l s the amplifier
bias so t h a t t h e data o n the disc is identical t o t h a t read by t h e
player, t h e r e b y d e c r e a s i n g error.
1 - 2 - 4 Envelope detection
T h e signal f r o m pin 4 of IC6 is f u r t h e r a m p l i f i e d a n d applied t o
the base of Q 2 1 . T h e variation in a m p l i t u d e of the DC c o m p o ­
nent, t h a t is e q u i v a l e n t t o t h e a m p l i t u d e of the EFM signal
w a v e , a p p e a r s in the e m i t t e r of Q 2 1 . This DC c o m p o n e n t is
a m p l i f i e d o n l y in l o w f r e q u e n c y by IC8 ( 1 / 2 ) a n d applied t o
the gate of AGC FET Q 3 3 , t h u s r e d u c i n g the c h a n g e in EFM
signal. In a d d i t i o n , t h e EFM signal is l e v e l - c o m p a r e d in IC10
( 1 / 2 ) . T h e n " L " at pin 1 of IC10 ( 1 / 2 ) i n f o r m s t o pins 2 0
(RFOK) of IC15 o n SERVO ( x 2 9 ) PCB a n d 2 9 (RFOK) of
IC15 o n t h e p r o c e s s ( X 3 2 ) PCB t h r o u g h pin 1 of C N 7 t h a t t h e
EFM signal is p r o v i d e d .
In a d d i t i o n , t h e EFM signal is also applied t o IC10 ( 2 / 2 ) via
diode D 1 9 f o r l e v e l - c o m p a r i n g . T h e n , it is o u t p u t f r o m pin 8
as signal RFES. T h i s signal is used in d r o p o u t c o n t r o l o n play
or used in t h e kick p r o c e s s i n g c i r c u i t at kick of m o t o r .
1 - 2 - 5 Pickup carry motor driver
A s play a d v a n c e s t r a c i n g the disc pit s e q u e n c e by t h e p i c k u p ,
a positive offset v o l t a g e a p p e a r s at t h e o u t p u t of t r a c k i n g coil
driver pin 8 of IC2 ( 2 / 2 ) by the t r a c k i n g servo f u n c t i o n . Since
the h i g h - f r e q u e n c y c o m p o n e n t , w h i c h is also c o n t a i n e d in t h e
t r a c k i n g driver o u t p u t besides the
necessary f o r d r i v i n g t h e p i c k u p c a r r y m o t o r , it is e l i m i n a t e d
by an LPF a m p l i f i e r of IC3 ( 2 / 2 ) . Further, this o u t p u t is p o w e r -
a m p l i f i e d in IC4 ( 2 / 2 ) t o drive t h e p i c k u p carry m o t o r .
In a d d i t i o n , Q 1 4 is ON t o avoid a p p l i c a t i o n of the t r a c k i n g ser­
v o o u t p u t signal d u r i n g m o d e s o t h e r t h a n play. Signal PUFB,
w h i c h is e n t e r e d t o t h e i n p u t of the p o w e r amplifier (pin 3 of
IC4 ( 2 / 2 ) ) , is used in kick o p e r a t i o n or fast m o v e m e n t of the
p i c k u p .
1 - 2 - 6 D i s c motor driver
W h e n pin 15 (MSP) of IC15 o n the servo PCB e m i t s an " H "
signal a c c o r d i n g t o t h e CPU c o m m a n d , the gate of Q 1 7
b e c o m e s " L " a n d Q 1 7 t u r n s OFF. Disc m o t o r driver IC4
( 1 / 2 ) c a n a m p l i f y signal AFC e m i t t e d f r o m IC8 o n the process
PCB due t o start t h e disc m o t o r . Due t o shorten t h e start t i m e
or t h e s t o p t i m e , a c i r c u i t c o n s i s t i n g of Q 1 9 , C 3 6 , Q 1 8 a n d
R 9 4 applies positive or negative pulse t o the pin 7 of IC4
( 1 / 2 ) . (Positive pulse at m o t o r ' s start Negative
m o t o r ' s s t o p ) .
offset v o l t a g e , is u n ­
pulse at