Teac MV1421, Service Manual

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7-12. Horizontal deflection
T h e circ u it co n ta in s H d rive , line o u tp u t tra n s fo rm e r.
T h e H d rive p ulse s fro m th e T D A 8 3 7 4 a re a m p lifie d in th e ho riz o n ta l d rive circ u it, to g e t s ufficie n t b a s e
d rive cu rre n t fo r th e h ig h v o lta ge s w itc hin g tra n s isto r Q 4 0 2 .
D u rin g th e h o riz o n ta l s ca n pe rio d (= 5 2 ) Q 4 0 2 w ill co n d u c t, a n d a sa w to o th c u rre n t flo w s fro m + 1 23 V
th ro u g h th e p rim a ry w in d in g o f th e F B T to g ro u n d .
A fte r th is tim e Q 4 0 2 is s w itc h e d -o ff a n d th e e n e rgy sto re d in th e F B T d u rin g th e s ca n p e rio d w ill b e
tra n s fo rm e d to th e flyb a c k c a pa c ito r C 40 6 , C 4 1 6 .
T h is e n e rg y tra n s fe r w ill ta k e p la c e in a c o sin e s h ap e b e ca u s e th e p rim a ry o f th e F B T a n d C 4 0 6 ,
4 1 6 fro m a re s o n a n t circ u it.
T h e tim e th e e n erg y is tra n sfe re d fro m F B T to C 4 06 ,4 1 6 a n d b a c k to th e F B T, is c a lle d th e flyb a c k tim e
a n d w ill ta k e p la c e in a b o u t 1 2 .
T h e fly b a ck p e a k v o lta g e is a b o u t 8 tim e s th e sc a n v o lta g e .
In se rie s w ith the h o rizo n ta l d e fle ctio n c o il th e re is a (d a m pe d ) lin e a rity c o rre c to r c o il.
D u rin g th e sc a n th e re is s o m e lo s s in th e re s ista n ce o f th e de fle c tio n c o il.
In th e first p a rt of a lin e th e line a rity co rre c to r s to re s s o m e e n e rg y in a p e rm an e n t m a g ne t u n til it is s a tu ra te d.
T h is im p rov e s the lin e a rity o f th e h o rizo n ta l s c a n s pe e d .
T h e re q u ire d S -c o rrec tio n fo r th e p ic tu re tu b e c a n b e a d ju ste d w ith th e va lu e o f C 4 1 5 .
T h e be a m c u rre n t lim itin g in fo rm a tio n is d e riv e d fro m the fo o t o f th e H .V w in d in g o f th e F B T.
T h is is co n n e c te d v ia re s is to r to + 8 V.
A s th e b e a m c u rre n t in c re a s e , th e v o lta ge o n lin e b e a m c u rre n t d e c re a s e s.
B e a m c u rre n t is d a m p e d b y a in te g ra tio n filte r be fo re it is fe d b ac k to T D A 83 7 4 p in 2 2 .
T h e T D A 8 3 7 4 w ill d e cre a s e th e co n tra s t(a n d e v e n tu a lly th e b rig h tn es s )to lim it the a ve ra g e b e a m c urre n t.
7-13. Video amplifiers
T h re e T D A 6 1 06 Q in te g ra te d vid eo a m p lifie rs d rive ca th od e o f th e p ictu re tu b e d ire c tly.
T h e y a re p ro te c te d a ga ins t C R T fla s h o ve r d is c h a rg e s a n d E S D (e lec tro sta tic d isc h a rg e ).
T h e th re e v id e o a m p lifie rs, h a v e a b e am c u rre n t o u tp u t I b la c k, u s e d b y th e T D A 83 7 4 b la ck c u rre n t lo o p
to co n trol the b la c k le ve l o n th e c a th o d e s.
T h e ou tp u ts c a n b e co n n e c te d to g e th e r b e c a us e th e b la c k c u rre n t lo o p s e q u e n tia lly c o n tro ls th e b la c k
le v e l fo r e a ch ca th o d e.
T h e am p lifica tio n o f th e T D A 6 1 0 6 Q is se t b y th e re sisto rs b e tw ee n p in 3 a n d 9 a n d b etw e e n p in 3
(n e g ativ e -in p u t) a n d th e T D A 83 7 4 o u tp u t.
T h e re a re n o a lig n m e n t a n y m o re o n th e C P T p an e l, b e c a u se o f th e a u to m a tic b la ck c u rre n t s ta b iliza tio n
a n d b e c a u se th e w h ite p o in t a d ju s tm e n t c a n b e do n e in th e T D A 83 7 4 via IIC b u s .