Teac MV1421, Руководство по обслуживанию

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D u rin g th e m e a s urin g lin e s R G B o u t w ill su p p ly 4 V p u ls e s to th e vid e o o u tp u t s ta g e s.
T h e T D A 8 3 7 4 w a its u ntil th e bla ck c u rre n t fee d b a c k in p u t (pin 18 ) e xc e e d s 2 0 0 , w h ic h in d ica te s th a t
th e p ictu re tu b e w arm -u p .
T h e n th e b la c k c u rre n t sta biliz a tio n circ u it is a c tiv e .
A fte r a w a itin g tim e o f a b o u t 1 .0 s e c, th e b la n kin g o f R G B o u t is re le a s ed .
7-8. Tuning
T h e A F C in fo rm a tio n o f th e T D A 8 3 7 4 is n o t a v a ila b le as an a n a lo g u e v o lta g e .
A u to m a tic fo llow in g (= fre q u en c y tra c kin g, A F C ) c a n b e d o n e via th e IIC b u s b y so ftw a re .
T h e T D A 8 3 7 4 A F C w in d o w is typ ica lly 8 0 k H z w id e .
T h is v a lu e is m a d e h ig h e r th a n the 6 2 .5 k H z tu n in g s tep , to p re ve n t a n au to m a tic fo llo w in g lo o p fro m
c o ntin u o u sly a d ap tin g th e tu n in g fre q u e n cy.
W ith th is A F C w in d o w ( 4 0 kH z ) th e m a xim u m tu n in g erro r is le s s tha n 6 2 .5 k H z .
F o r h ig h sp e e d se a rch -tun u n g -a lg o rith m s ,th e A F C w in d o w c a n b e w ide n e d to 24 0 k H z via b it A F W .
7-9. TDA8395 SECAM DECODER
T h e T D A 8 3 9 5 is a n a lig n m e n t-fre e S E C A M c olo u r d e co d e r, inc lu d in g a c lo ch e filte r, d e m o d u la to r a n d
lin e id e n tifica tio n c ircu it.
T h e clo c h e filte r is a g y ra to r-c a p a cito r typ e .
Its fre q u e n cy is ca lib ra te d in th e v e rtic a l re tra c e p e rio d .
T h e ca lib ra tio n re fe re n ce (p in 1 ) is o b ta in e d fro m th e T D A 8 3 7 4 c o lo u r X -ta l o s c illa to r.(p in 3 3 ).
P in 7 is a d e c o up lin g fo r th e c lo c h e re fe re n ce .
T h e vo lta g e c h an g e a t th is p in d u e to le a ka g e cu rre n ts s h o u ld b e lo w e r th a n 1 0 m V, d u rin g fie ld s c an ,
re su ltin g in a c a p a cito r if m in im a l 1 00 n F.
P in 8 is th e re fe re n c e c a p a cito r fo r th e P L L .
T h e vo lta g e va ria tion d u rin g fie ld sca n a t th is p in s h o u ld b e lo w e r th a n 2m V, re su ltin g in a c ap a c itor of 2 2 0 n F.
T h e sa n d c as tle in p u t (p in 1 5 ) is c o n ne c ted to T D A 8 3 7 4 p in 4 1 a n d is u s e d fo r g e n era tio n o f th e b la n kin g
p e rio d s a n d p ro vid e s c lo c k in fo rm a tio n fo r th e id e ntifica tio n c ircu it.
T h e C V B S s o u rc e se le c t o u tp u t (T D A 8 3 7 4 p in 3 8 ) s u p p lie s S E C A M c h ro m a to p in 16 o f th e T D A 8 3 9 5 .
T h is is d em o d u la te d b y a P L L d e m o d u la to r, th a t u se s th e re fe re n c e fre q u e n cy at p in 1 a n d a b a n d g a p
re fe re n ce to ob ta in th e d e s ired d e m o d u la tio n c ha ra c te ris tic .
If th e d ig ita l lin e id e n tific a tio n in th e T D A 83 9 5 d e te c ts S E C A M , p in 1 w ill s in k a c u rre n t o f 1 5 0 ß À o u t of
T D A 8 3 7 4 S E C A M ref p in 3 3 .
W h e n th e T D A 8 3 7 4 h a s n ot d e te cte d PA L o r N T S C , w ill re sp o n d b y in c re a s in g th e v o lta g e a t pin 33 fro m
1 .5 V to 5 V. N ow th e T D A 8 3 7 4 c o lo u r d iffe re n ce o u tp u ts p in 3 0 a n d 2 9 are m a d e h ig h -o h m ic a n d th e
T D A 8 3 9 5 o u tp u t p in 9 a n d 1 0 a re s w itc h e d o n .
T h e s e o u tp u ts w ill be d is co n n e c te d a n d h ig h -o h m ic w he n n o S E C A M is d e te cte d fo r tw o fra m e p e rio d s ,
th e d e co d e r w ill b e in itia liz e d b e fo re try in g a g a in .