Kenwood DP-1100 B Service Manual page 39

1 - 5 - 4 F O C U S S E A R C H O P E R A T I O N
W h e n a disc is set a n d the tray is c l o s e d , a signal of 2 Hz
is o u t p u t m a x i m u m f o u r t i m e s to pin 3 6 of m i c r o p r o c e s s o r
IC15 ( T M P 4 7 4 0 N ) . This signal c o n f i r m s that the disc has
been p r o p e r l y set a n d prepares for f o c u s servo o p e r a t i o n .
The f o c u s servo m a i n t a i n s a c o n s t a n t position of the pick­
u p lens against the disc so t h a t the size of the f o c u s e d laser
s p o t is kept c o n s t a n t as a result. If the distance b e t w e e n
the p i c k u p a n d the disc is t o o far or t o o c l o s e , a proper size
of the laser s p o t c a n n o t be o b t a i n e d o n the disc s u r f a c e , in
a n o t h e r w o r d s , n o t properly f o c u s e d .
Disc
- L a s e r Beam
Lens
Pickup
4 2
D P - 1 1 0 0 B I] D P - 1 1 0 0 B II
1. CIRCUIT DESCRIPTION
Fig. 1-5-4-1
3. A proper size of the laser s p o t is p r o v i d e d o n t h e disc sur­
f a c e by m o v i n g the p i c k u p lens u p a n d d o w n using the
2 Hz signal. This is called f o c u s search o p e r a t i o n . O n c e it
is f o c u s e d , the search signal is d i s c o n t i n u e d .
4 . T h e o u t p u t signal f r o m pin 3 6 of m i c r o p r o c e s s o r IC15 is
applied t o pin 4 of f o c u s coil drive a m p IC2 ( 1 / 2 ) via R 1 4 ,
R17 a n d R 1 8 . (The f o c u s coil m o v e s t h e p i c k u p lens up
a n d d o w n . ) Its o u t p u t a p p e a r s at pin 2 a n d is applied
across the f o c u s coil t o m o v e t h e lens u p a n d d o w n .
5. C5 in the a b o v e s c h e m a t i c d i a g r a m c u t s off t h e DC c o m ­
p o n e n t of the signal a n d R 6 , C 4 , R 1 4 a n d C 6 f o r m a LPF
to eliminate f r e q u e n c y c o m p o n e n t s h i g h e r t h a n 2 Hz.
6. The phase c o m p e n s a t i o n c i r c u i t ( c o m p e n s a t e s the fre­
q u e n c y characteristic a n d phase charateristic of the
p i c k u p ) in the a b o v e d i a g r a m is for t h e f o c u s servo pur­
pose. Refer to f o c u s servo o p e r a t i o n ( 1 - 5 - 7 ) .
F i g . 1 - 5 - 4 - 2 Operation Timing of F o c u s S e a r c h