Kenwood DP-1100 B Service Manual page 40

1 - 5 - 5 D I S C D E T E C T I O N O P E R A T I O N & R E V E R S E - R E V O L U T I O N P R E V E N T I O N C I R C U I T F O R D I S C M O T O R
1 . A n RF signal is p r o d u c e d by a d d i n g o u t p u t signals S i
( A + A ) a n d S ( A + A ) f r o m the 4 - d e v i s i o n p h o t o d e t e c -
1 3 2 2 4
tor t h r o u g h R 1 0 1 a n d R 1 0 0 a n d a m p l i f i e d t o an a d e q u a t e
level. It is t h e n e n v e l o p e d e t e c t e d by Q 2 1 . The d e t e c t e d
signal is a p p l i e d t o pin 3 of IC10 ( 1 / 2 ) . On the other h a n d ,
a signal of reference level ( a b o u t 0 . 8 V ) , w h i c h is divided
by resistors, is f e d to pin 4 of IC10 ( 1 / 2 ) . The d e t e c t e d
signal a n d r e f e r e n c e level is c o m p a r e d a n d o u t p u t to pin 2 .
T h a t is, w h e n t h e e n v e l o p e of RF signal is over 0 . 8 V , " L "
( a b o u t 0 V) o u t p u t results a n d w h e n it is less t h a n 0 . 8 V ,
" H " ( a b o u t 5 V) results.
2 . The t i m e c o n s t a n t for transition t o " H " signal or t o " L "
signal is different. T h e t i m e c o n s t a n t for transition to " H "
is d e t e r m i n e d by C 5 4 a n d R 1 4 9 , a n d the t i m e c o n s t a n t
for it t o " L " is d e t e r m i n e d by C 5 4 a n d R 1 4 0 . T h e t i m e
c o n s t a n t for " H " is a b o u t 1 0 0 0 t i m e s larger t h a n that for
" L " . This prevents the o u t p u t f r o m a c c i d e n t a l l y b e c o m i n g
" H " b e c a u s e of d r o p o u t s of RF signals c a u s e d by scrat­
c h e s or d u s t s . It also falls t o " L " q u i c k l y , w h e n RF signal
(RFOK Signal) is d e t e c t e d .
D P - 1 1 0 0 B II I D P - 1 1 0 0 B II
1. CIRCUIT DESCRIPTION
3 . The RFOK signal is to j u d g e the presense of RF signal as
e x p l a i n e d a b o v e , it results in " L " w h e n the RF signal is
present a n d it results in " H " w h e n n o t present. Both of the
MSP a n d RFOK signals are " H " , w h e n the disc m o t o r
starts r u n n i n g (initial start f r o m a c o m p l e t e s t o p state.)
Q 3 1 a n d Q 1 9 g o to OFF, w h i l e Q 1 8 is O N . This increases
a negative voltage at pin 8 of IC4 ( 1 / 2 ) , t h e r e b y p r e v e n ­
t i n g the disc m o t o r f r o m revolving in t h e reverse d i r e c t i o n .
Fig. 1 - 5 - 5
4 3