Track Control; Adjustment Of The Output Level; Quiescent Current; The Bass Control - TANDBERG 12 Service Manual

5 . 6 T R A C K . C O N T R O I , . M O D E L . | 2 - 2
W I T H O U T TANDBERG TEST TAPES
5.6.t The erase head
T h e h e i g h t o f t h e e r a s e h e a d i s a l i g n e d b y t h e h e i g h t
a d [ u s t m e n t s c r e w s . R e f . f i g . l l . T h e t a p e s h a l l r u n
e q u i d i s t a n t f r o m t h e u p p e r a n d t h e l o w e r e d g e o f t h e
ferrile core.
F o r t h e a z i m u t h a n d l a t e r a l a l i q n m e n t s r e f . c h a p t e r
5 . 4 . 4 .
5.6.2 The record/playback head
T h e h e i g h t o f t h e r e c o r d / p l a y b a c k h e a d i s a l i g n e d b y
t h e h e i g h t a d l u s t m e n t s c r e w s r e f . f i g . I | . R e c o r d a
l 0 0 O c / s s i g n a l i n s t e r e o ( b o f h f u n c t i o n s e l e c t o r
switches are set to <RECORD> pos.), at maximum re-
cording level on a full track pre-recorded iape. Dip the
t a p e i n t h e M a g n a - S e e s o l u t i o n a n d c h e c k t h a t t h e
t r a c k s a r e d i s t r i b u t e d s y m m e t r i c a l a c r o s s t h e t a p e , a n d
that the pre-recorded zone remains in the center of
the erased zone. Readiust the erase and record heads,
if necessary.
F o r t h e a z i m u t h a n d t h e l a t e r a l a l i q n m e n l r e f . c h a p t e r
5 . 4 . 3 .
5.7 ELECTRICAT ADJUSTMENTS FOR TANDBERG
TAPE RECORDER MODETS I2_4 AND I2_2
5.7.1 Adiuslmenls of the power output amplifier
C o n n e c t t h e a u d i o g e n e r a t o r f o t h e H I G H L E V E L i n -
p u t c h . I ( c h . 2 ) a n d s e t t h e f r e q u e n c y t o 1 0 0 0 c / s .
A 4 ohms, l5 watfs load resistor is connected to the
e x t e r n a l o u t p u t t e r m i n a l s c h . I ( c h . 2 ) . C o n n e c t a
V T V M a n d a n o s c i l l o s c o p e p a r a l l e l t h e l o a d r e s i s t o r .
Set both funcfion selector switches to position AMP.
( s t e r e o a m p l i f i e r ) . T h e v o l u m e c o n t r o l s R l - c h . I a n d
R 2 - c h . 2 s h o u l d b e s e f t o m a x . a n d t h e s p e a k e r
selector to position EXT.
Set the bass controls and the treble controls lo zero.
5.7.2 Adlustmenl of the output level
I n c r e a s e t h e o u t p u t l e v e l f r o m t h e g e n e r a t o r u n t i i
c l i p p i n g o c c u r s o n t h e s c o p e . A d i u s t t h e p o t e n t i o -
m e t e r R 3 0 5 - c h . I ( R 4 0 5 - c h . 2 ) u n t i l s y m m e t r i c a l
c l i p p i n g o f t h e p o s i t i v e a n d t h e n e g a t i v e h a l f - p e r i o d s
i s o b t a i n e d .
Decrease the output level from the audio generator
u n t i l t h e c l i p p i n g d i s a p p e a r s . T h e V T V M s h o u l d t h e n
r e a d m i n . 6 , 3 v o l t s f o r b o t h c h a n n e l s ( c o r r e s p o n d s t o
i 0 w a t t s i n 4 o h m s ) . T h e t o l e r a n c e o f t h e o u l p u t l e v e l
b e t w e e n t h e t w o c h a n n e l s i s 2 d B .
5.7.3 Quiescenl currenl
S e t t h e v o l u m e c o n t r o l R l - c h . I a n d R 2 - c h . 2 t o
zero. Connect a mA-meier in series with * 27 volts
s u p p l y t o t h e p o w e r o u t p u t a m p l i f i e r f o r c h . i , r e d
w i r e ( c h . 2 r e d w i r e ) . A d i u s i R 3 l 0 - c h . I ( R 4 1 0 -
c h . 2 ) f o 3 5 m A .
5.7.4 Adiuslmenl of rhe FM MX-filter.
Connect the test equipment to the tape recorder as
d e s c r i b e d u n d e r o a r a . 5 . 7 . . | .
A d i u s r t h e o u t p u t o f 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
VTVM reads lV at ]000 c/s. Set the FM MX-filter
s w i t c h t o p o s i t i o n O N .
Set the generator to l9Kc/s and adiust L4 - ch. I (15
36
- c h . 2 ) t o m i n . d e f l e c t i o n o n i h e V T V M . T h e a t t e n u a -
t i o n b e t w e e n t h e s i g n a l l e v e l s a t 1 0 0 0 c / s a n d a t
l 9 K c / s s h o u l d b e m o r e t h a n 2 3 d B .
T h e a d j u s t m e n t p r o c e d u r e f o r a l i g n i n g t h e 3 3 , 3 k c / s
FM-MX filter is exactly lhe same as outlined for the
1 9 k c / s f i l t e r e x c e p t f o r t h e g e n e r a t o r f r e q u e n c y
w h i c h s h o u l d b e s e t r o 3 3 , 3 k c / s . T h e d i f f e r e n c e i n
s i g n a l l e v e l b e t w e e n I 0 0 0 c / s a n d 3 3 , 3 k c / s s h o u l d
b e m o r e t h a n I B d B .
5.7.5 Control of the frequency response in AMP.
position
Connect the test equipment to the tape recorder as
d e s c r i b e d u n d e r p a r a . 5 . 7 . . | . S e t f h e F M M X - f i l t e r
switch to position OFF. Adiust the output level of the
a u d i o g e n e r a t o r u n t i l t h e V T V M r e a d s 5 0 0 m V .
T h e f r e q u e n c y r e s p o n s e : t 2 d B 3 0 - 1 6 0 0 0 c / s .
5.7.6 The bass control
T h e a u d i o g e n e r a t o r i s s e t t o
. I 0 0 0 c / s .
T h e o u i p u t
l e v e l f r o m t h e g e n e r a t o r i s a d i u s t e d u n t i l t h e V T V M
reads 500 mV. Turn the bass control on the lape re-
corder up to max. (pos. 6). Reset the generator to
I00 c/s, the output level from the tape recorder
s h o u l d n o w i n c r e a s e a p p r o x . l 0 d B .
5.7.7 lhe lreble control
T h e a u d i o g e n e r a t o r i s s e t t o 1 0 0 0 c / s . T h e o u t p u t
l e v e l f r o m t h e g e n e r a t o r i s a d i u s t e d u n t i l t h e V T V M
r e a d s 5 0 0 m V . T u r n t h e t r e b l e c o n t r o l o n t h e t a p e r e -
corder down to min. (pos. 6). Reset the generator to
1 0 0 0 0 c / s , l h e o u t p u t l e v e l f r o m t h e t a p e r e c o r d e r
s h o u l d n o w d e c r e a s e a p p r o x . l 2 d B .
5,7.8 Adiuslment of the record current and the
electronic beam indicalor circuils
C o n n e c t i o n s :
C o n n e c f i h e a u d i o g e n e r a t o r f o t h e H I G H L E V E L i n p u t
c h . I ( c h . 2 ) .
C o n n e c t t h e V T V M t o t h e w i p e r o f t h e v o l u m e c o n t r o l
c h . I t e r m i n a l 2 4 k h . 2 t e r m i n a l 4 5 ) .
Set both function selector switches to position REC
(stereo record), and move the operating lever to the
position normal forward drive at the tape speed 7th
i . P ' s .
A 1 0 0 o h m s r e s i s l o r i s c o n n e c t e d i n s e r i e s w i t h t h e
u p p e r ( l o w e r ) r e c o r d / p l a y b a c k h e a d t o g r o u n d c h . I
( r e d w i r e c h . l , b l u e w i r e c h . 2 ) . S e f l h e v o l u m e c o n -
trols to the postion 3. Siop the oscillator by shortcir-
c u i t i n g f h e s e c o n d a r y w i n d i n g s o f t h e o s c i l l a t o r c o i l .
5.7.9 The electronic beam indicators
S e t t h e a u d i o g e n e r a t o r t o 1 0 0 0 c / s a n d a d i u s t t h e
output level from the generator until the VTVM reads
5 0 m V .
A d i u s t R 6 0 1 - c h . I ( R 6 0 5 -
c h . 2 ) 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 .
5.7.1O The record currenl
Connect the VTVM across the
.|00
ohms resistor in
s e r i e s w i t h t h e r e c o r d h e a d . A d i u s r R l 4 - c h . l ( R l 5
-
c h . 2 ) u n t i l i h e r e a d i n g o n t h e V T V M i s 1 3 m V .
( T h e r e a d i n g f o r t h e t w o - t r a c k m o d e l s h o u l d b e
l 8 m V . )
q
F
(