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Video Output
The video output stage utilizes the parts listed below to produce and
control the picture:
F i n a l P a r t s i n t h e V i d e o O u t p u t S t a g e
P a r t
L o c a t i o n
Y / C J u n g l e
M a i n A
b o a r d
I C 3 0 1
C R T A m p I C 7 0 1
C
b o a r d
P i c t u r e t u b e
F r o n t c a b i n e t
b e z e l
Video signal Path
Y/C Jungle IC301
Within Y/C Jungle IC301, the input signal is selected, processed and
converted to RGB. The RGB signal undergoes some final processing
before leaving the Jungle IC301.
L a t e r P r o c e s s i n g I n t e r n a l t o I C 3 0 1
P r o c e s s i n g
O p e r a t i o n
S t a g e
O S D
M i x e r
T h e O S D
c h a r a c t e r s r e p l a c e
t h e R G B
s i g n a l .
B l a n k i n g
U s e s A B L s i g n a l f r o m
F B T t o r e d u c e R G B
v o l t a g e .
B l a n k ( g n d ) t h e R G B
s i g n a l a n d i n s t r u c t s I C 0 0 1 t o
s h u t o f f t h e T V
g r o u n d a t I C 3 0 1 / p i n 1 8 .
G a i n C o n t r o l
T h e g a i n a n d l e v e l o f t h e
R G B
s i g n a l s i s s e t b y I
c o m m u n i c a t i o n s d a t a ( S D A )
b e f o r e o u t p u t .
c a t h o d e c u r r e n t ( I K )
f e e d b a c k i s u s e d t o m a i n t a i n
R G B l e v e l s .
P u r p o s e
S e p a r a t e s v i d e o i n t o Y &
c o m p o n e n t s w h e n t h e r e i s n o
e x t e r n a l c o m b f i l t e r .
U s e s t h e Y
( B & W ) s i g n a l t o a d j u s t
t h e R G B
o u t p u t v o l t a g e l e v e l .
S e p a r a t e s t h e C
i n p u t i n t o R G B
v o l t a g e s .
A d j u s t s R G B d r i v e l e v e l s t o
m a i n t a i n p r e s e t c a t h o d e c u r r e n t .
R e q . I K f e e d b a c k s i g n a l .
A m p l i f i e s t h e R G B
d r i v e s i g n a l
P r o d u c e a c o l o r p i c t u r e .
P u r p o s e
I n s e r t O S D
o r C C
c h a r a c t e r s i n t o t h e
p i c t u r e .
t h e
U s e s F B T h i g h
d r i v e
v o l t a g e t o l i m i t t h e
b r i g h t n e s s o f t h e
p i c t u r e .
O u t p u t
E x c e s s i v e F B T
i f t h e r e i s a
v o l t a g e o r B + c u r r e n t
w i l l c a u s e I C 3 0 1 / p i n
1 8 t o b e g r o u n d e d .
I C 3 0 1 i n f o r m s I C 0 0 1
t o p r o t e c t t h e T V b y
t u r n i n g t h e T V
M a i n t a i n s g o o d w h i t e
2
C
b a l a n c e .
P i c t u r e t u b e
73
Video Buffers
These three buffer transistors provide current drive to sink the current
from IC701. A short in one of these transistors would stop that color (and
activate blanking via the IK circuit). An open transistor will cause that
color to go to a high brightness (with retrace lines).
CRT Amplifier
This IC package amplifies the RGB signal from the buffers to a sufficient
C
voltage to drive the cathodes of the picture tube.
Cathode Current Adjusting (IK) Circuit
Concept
As the picture tube ages, the electron output of the three cathode struc-
tures will no longer be the same. The cathode current (IK) circuit moni-
tors the current of each cathode and adjusts the electronic drive signal
level to compensate for the differences due to aging. As the tube is
being used, normal wear causes the cathodes to decrease in output at
different rates. When one cathode has dropped in output below the
others, white color no longer appears white. White balance is now "off".
Increasing one of the R, G or B drive signal levels to the deficient cath-
ode increases that cathode's electron emission so its output will be like
the others. The picture quality can be automatically maintained with this
circuit.
Circuitry
The automatic cathode current adjusting circuit keeps the video and OSD
blanked until the AKB circuit has finished. The Y/C Jungle IC301 gener-
ates the cathode drive pulse to begin the IK circuit operation. Three
horizontal lines in the vertical interval of the field above the picture are
used to test each cathode, one at a time.
ON, starting with the Red output at pin 22. After the first pulse at pin 22,
IC301/pin 23 sends a 10usec pulse to turn on the green cathode for the
entire horizontal line. After the pulse at IC301/pin 23 returns LOW, pin
O F F .
24 outputs the last pulse to turn on the blue cathode. These 10usec.
width positive drive pulses are buffered by Q392-Q394 and amplified by
IC701 to be applied to the picture tube cathodes.
Each cathode is driven full
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