Sony CTV-25R1 Manual page 81

Troubleshooting
The IK circuit may keep the set in blanking because:
•
The picture tube is old and the amplitude of the IK feedback pulses is
too low to permit automatic cathode adjustment
•
One or more of the IK pulses is not output to the CRT
•
One or more of the IK pulses is not returned to the Jungle IC301/pin
21.
Turning up the screen control will permit you to see if a color is missing. If
there is a color missing, the problem is between the Jungle IC and the
picture tube cathodes.
If all three colors are present, the defect is in the IK return/feedback line
between IC701/pin 5 and Jungle IC301/pin 21. While the unit is in blank-
ing, use your scope to look for the three positive IK pulses from the Jungle
IC301/pin 22-24 back to pin 21.
77
C o m p o n e n t S ig n a l I n
I C 3 0 1 / p i n s
2 2 , 2 3 , 2 4
Q 3 9 2 - Q 3 9 4
I C 7 0 1 P o s it iv e p u ls e s
B la n k e d P ix . =
3 . 2 V p - p . I K
p u l s e + 0 . 2 V p -
p o f r e s id u a l
h o r iz . p u l s e s a t
t h e b o t t o m .
N o r m a l p ix . =
2 V p - p
I C 7 0 1 P o s it iv e p u ls e s
B la n k e d P ix . =
3 . 2 V p - p . I K
p u l s e + 0 . 2 V p -
p o f r e s id u a l
h o r iz . p u l s e s a t
t h e b o t t o m .
N o r m a l P ix . =
2 V p - p
Q 3 0 1 , Q 3 0 2 I n p u t s a m e a s
I C 7 0 1 / p i n 5 .
I C 3 0 1 / p i n S a m e a s
2 1 Q 3 0 1 / C
( O u t p u t )
I K S I G N A L P A T H
S ig n a l O u t
P o s it iv e p u ls e D r i v e t h e
p ic t u r e t u b e
B la n k e d P ix . =
c a t h o d e d u r in g
3 . 6 V p - p . I K s i g n a l.
t h e t e s t
N o r m a l P ix . - 2 V p - p
in t e r v a l.
S a m e a s a b o v e . B u ffe r s .
P in s 7 - 9 : N e g . A m p lify t h e
p u l s e s 3 . 2 V p - p IK t e s t
s ig n a l a n d
B la n k e d P ix . =
0 . 2 V p - p
1 8 0 V p - p I K p u ls e s .
h o r iz o n t a l
N o r m a l P ix . = s ig n a l t o t h e
p ic t u r e t u b e .
1 8 0 V p - p o f R , G , o r
B s ig n a l w it h a
1 2 0 V p - p I K n e g .
p u l s e .
P in 5 : S u p p ly a
c o m p o s i t e
B la n k e d P ix . = 3 V p -
R G B o u t p u t
p h o r iz o n t a l p u ls e s
s ig n a l a t p in 5
w it h a 0 . 7 V p - p
t o m o n it o r in g
p o s it iv e I K s ig n a l.
c a t h o d e
N o r m a l P ix . =
c u r r e n t
3 . 5 V p - p R G B
s ig n a l w it h 1 1 0 V p - p
p o s it iv e I K s ig n a l
O u t p u t Q 3 0 1 / C C lip t h e lo w e r
p o r t io n o f t h e
B la n k e d P ix . =
w a v e f o r m .
0 . 4 V p - p o f h o r iz
L im it t h e
s ig n a l w it h a 0 . 1 V p -
a m p lit u d e o f
p p o s it iv e I K p u ls e .
t h e o v e r a ll
N o r m a l P ix . =
s ig n a l.
1 . 5 V p - p R G B
s ig n a l w it h a 0 . 2
p o s it iv e I K p u ls e .
E x t r a c t IK
p u l s e s a n d u s e
t h e m t o a d ju s t
R G B le v e ls
a n d u n b la n k
t h e v id e o .
P u r p o s e