Circuit Description; Head Amplifier - Kenwood DP-1100 B Service Manual

S u b s e q u e n t t o " 1 - 2 H e a d a m p " , t h e servo PCB a n d t h e
p r o c e s s PCB are d e s c r i b e d in o r d e r a l o n g the RF signal f l o w .

1-1 Head amplifier

T h e f o u r signals f r o m t h e p i c k u p are i n p u t t o preamplifier IC
( Q 1 0 3 ) o n the m e c h a n i s m PCB.
1- 1-1 F o c u s b a l a n c e a n d S V C operation circuit ( Q 1 0 3 )
T h e internal b l o c k d i a g r a m of Q 1 0 3 is s h o w n in section
2 - 1 - 1 . T h r o u g h t h e resistors, c o n n e c t e d b e t w e e n pins 1 a n d
2 a n d b e t w e e n pins 15 a n d 16 of Q 1 0 3 ( T A 7 7 3 1 P ) , f o c u s
b a l a n c e a n d SVC o p e r a t i o n (described later) are p e r f o r m e d .
W e a k signal is a m p l i f i e d a n d o u t p u t t o servo PCB as S1 a n d
S 2 .
1-1-2 F o c u s error signal generation circuit ( Q 1 0 1 and Q 1 0 4 )
T h e FE amplifier a n d peak d e t e c t o r , c o n s i s t i n g of Q 1 0 1 a n d
Q 1 0 4 , is a c i r c u i t t o g e n e r a t e t h e f o c u s error signal. Peak
d e t e c t i o n is m a d e w i t h t h e B-E d i o d e characteristic of Q 1 0 4
a n d t h e CR t i m e c o n s t a n t of its e m i t t e r . T h e f o c u s error signal
is o b t a i n e d f r o m (C + D) - (A + B) o p e r a t i o n of the p i c k e d - u p
f o u r signals f r o m t h e p i c k u p by Q 1 0 1 .
1 - 1 - 3 S V C circuit operation ( Q 1 0 2 )
T h e servo c o n t r o l (SVC) is p e r f o r m e d by processor IC12 o n
the p r o c e s s PCB ( X 3 2 - 1 0 1 0 ) , w h e n t h e disc is e x c h a n g e d or

1. CIRCUIT DESCRIPTION

Fig. 1 - 1 - 3 S V C Circuit Operation
w h e n play m o d e is e n t e r e d f r o m s t o p m o d e . It c h e c k s t h e
n u m b e r of data errors to c o n t r o l c o n t r o l i n p u t s A , B, C a n d
INH of Q 1 0 2 o n t h e m e c h a n i s m PCB t o o b t a i n t h e o p t i m u m
p l a y b a c k .
T h e internal block d i a g r a m a n d t r u t h table of Q 1 0 2 is s h o w n
in Fig 2-1 C a n d D of s e c t i o n 2 - 1 - 2 . Inputs A , B, C a n d I N H ,
d e t e r m i n e w h i c h o u t p u t 0 t o 7 (bilateral s w i t c h s h o u l d be i n ­
ternally c o n n e c t e d w i t h C O M ) .
1 - 1 - 4 A P C (laser p o w e r control) circuit ( Q 1 0 5 , Q 1 0 6 a n d
Q 1 0 7 )
Q 1 0 5 , w h i c h is the laser O N / O F F s w i t c h , t u r n s O N w i t h " L "
signal LDC (J8-3P) f r o m the m i c r o p r o c e s s o r so t h a t t h e laser
d i o d e e m i t s light. T h i s laser d i o d e i n c o r p o r a t e s a light e m i s ­
sion m o n i t o r d i o d e . T h e n , APC o p e r a t i o n is p e r f o r m e d by us­
ing t h e m o n i t o r o u t p u t as t h e APC c o n t r o l i n p u t .
1-1-5 F G amplifier circuit ( Q 1 0 1 ( 2 / 2 ) , Q 1 0 8 a n d Q 1 0 9 )
FG signal is p r o d u c e d by Q 1 0 1 , Q 1 0 8 a n d Q 1 0 9 t o m o n i t o r
t h e rotation of t h e disc m o t o r . Q 1 0 1 p e r f o r m s a m p l i f i c a t i o n
a n d Q 1 0 8 , Q 1 0 9 a n d D 1 0 4 p e r f o r m w a v e f o r m s h a p i n g . For
a d j u s t m e n t of e a c h t r i m m i n g p o t e n t i o m e t e r , refer t o " A d j u s t ­
m e n t " o n page 1 6 5 .
D P - 1 1 0 0 B II
3 3