Distortion; Balance Adjustment For The Pre-Amp. Outputs; Adjustment Of The Equalization Coils L1 And L2; Control Of The Recording Curves - TANDBERG 12 Service Manual

5 . 7 . 1 2 D i s t o r t i o n
C o n n e c t t h e t e s t e q u i p m e n t t o t h e t a p e r e c o r d e r a s
d e s c r i b e d u n d e r p a r a . 5 . 7 . I .
Set the function selector switches to REC position
( s t e r e o r e c o r d ) . C o n n e c t t h e a u d i o g e n e r a t o r t o t h e
H I G H L E V E L i n p u t s c h . I a n d c h . 2 a n d a d i u s t t h e
frequency to 400 c/s. Set the volume controls to
p o s i t i o n 3 a n d a d i u s t t h e a u d i o g e n e r a t o r u n t i l t h e
e l e c t r o n i c b e a m i n d i c a t o r s a r e c l o s i n g , a n d m a k e a
r e c o r d i n g f o r a b o u t 2 m i n . R e w i n d t h e t a p e a n d p l a y
i t b a c k i n s t e r e o .
T h e d i s t o r t i o n s h o u l d b e l e s s t h a n 3 - 5 % . l f t h e d i s -
tortion is above these tolerances the record current
m u s t b e r e a d i u s t e d .
Note: lf the record current is readiusted it will affect
t h e b i a s a n d t h e o s c i l l a t o r f r e q u e n c y , r e c h e c k
t h e r e f o r e b o t h t h e b i a s s e t t i n q a n d t h e o s c i l l a -
tor frequency.
5.7.13 Balance adiuslment for the pre-amp. outputs
Use a full track recorded tape 250 c/s (Tandberg test
t a p e n o . 3 ) . S e t t h e t a p e r e c o r d e r i n s t e r e o p l a y b a c k
mode. Connect a VTVM to both pre-amplifier outputs.
A d i u s t R 2 0 u n t i l b o f h V T V M h a v e t h e s a m e r e a d i n g .
5.7.14 Adiuslmeni of the equalization coils
L l a n d L 2
C o n n e c t t h e a u d i o g e n e r a t o r t o t h e H I G H L E V E L i n p u t s
c h . I a n d c h . 2 a n d s e t t h e f r e q u e n c y t o f :
I 8 0 0 0 c / s .
Set ihe speed selector switch to position 71/z i.p.s.
A d j u s t L l - c h . 1 ( 1 2 - c h . 2 ) t o m a x . d e f l e c t i o n o n t h e
e l e c t r o n i c b e a m i n d i c a t o r s .
5.7.15 Control of lhe recording curves
C o n n e c t t h e a u d i o g e n e r a t o r t o t h e H I G H L E V E L i n -
p u t s c h . I a n d c h . 2 . A V T V M i s c o n n e c t e d p a r a l l e l t o
1 0 0 o h m s r e s i s t o r s i n s e r i e s w i l h e a c h r e c o r d / p l a y -
b a c k h e a d ( c h . I a n d c h . 2 ) t o g r o u n d ( r e d a n d b l u e
w i r e s ) r e f . a d i u s t m e n t o f t h e r e c o r d c u r r e n t . S e t t h e
t a p e r e c o r d e r i n s t e r e o r e c o r d i n g a n d s w i t c h t h e
FM MX-filter ro OFF.
S h o r i c i r c u i t t h e s e c o n d a r y w i n d i n g o f t h e o s c i l l a t o r
t r a n s f o r m e r T 3 ( T l o n t h e t w o - t r a c k v e r s i o n ) .
T u n e t h e g e n e r a t o r t o 4 0 0 c / s a n d a d i u s t t h e o u l p u t
l e v e l f r o m t h e g e n e r a t o r 2 0 d B b e l o w m a x . r e c o r d i n g
l e v e l . C h e c k t h e f r e q u e n c y r e s p o n s e a c c o r d i n g i o
f i g . 4 3 .
T h e t o l e r a n c e s s h o u l d b e l e s s t h a n + 2 . 5 d B f o r a l l
frequencies. The difference in level between the two
c h a n n e l s s h o u l d b e l e s s t h a n 3 d B f o r a l l f r e o u e n c i e s .
Check the frequency response for all these speeds.
fil
4
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38
F i g . 5 4 . F r o n t v i e w o f t h e l o p e r e c o r d e r .