Sony DTV-01, Manual

Page: 92 / 132

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3. Connect the ohmmeter positive lead to the DRAIN.
If the device is good you will get a resistance reading of about 400-1k
ohms.
Driver PWM stage
The purpose of this stage is to make and regulate the driver’s drain volt-
age (Q4011) using a processed PWM signal. In addition, the supply volt-
age can be increased to widen the picture to fill the screen. The higher
drive voltage causes a larger signal that drives the output transistor harder.
The increased collector current cause more yoke current to create a larger
magnetic field to increase deflection and picture width.
This is series of processing steps that is used to make and control the
PWM signal:
P W M S t a g e
D e v ic e I n p u t O u t p u t P u r p o s e
Q 4 0 2 8 ,
C 4 0 0 6 C N 1 3 0 4 / 1 0
P o s it iv e p u ls e
a t t h e H . d r iv e
f r e q u e n c y I C 4 0 0 4 / 5 -
R a m p
v o lt a g e M a k e s a r a m p
v o lt a g e b y c h a r g in g
C 4 0 0 6 . D is c h a r g e s
w it h C N 1 3 0 4 / 1 0
p u ls e .
I C 4 0 0 4
c o m p a r a t o r R a m p v o lt a g e -
p in 5
D C v o lt a g e –
p in 6
I C 4 0 0 4 / 2 -
P o s it iv e
p u ls e D C v o lt a g e in p u t
c o n t r o ls p u ls e w id t h
( P W M ) .
Q 4 0 2 8 ,
Q 4 0 0 3 P o s it iv e p u ls e A m p lif ie d
p u ls e V o lt a g e / C u r r e n t
a m p .
D 4 0 0 2 ,
L 4 0 0 1 ,
C 4 0 0 3 . P W M s ig n a l D C v o lt a g e D a m p e r a n d lo w
p a s s f ilt e r .
I C 4 0 0 6 / p in s
1 - 3 S a m p le d D C
f r o m v o lt a g e
d iv id e r R 4 0 0 8 ,
R 4 0 1 1 , R 4 0 1 2
t o I C 4 0 0 6 / p in 3 . I C 4 0 0 6 / p in
1 – D C
v o lt a g e . D C r e g u la t io n .
Q 4 0 0 7 ,
I C 4 0 0 6 / p in s
5 - 7 . C N 4 0 0 7 / p in 1 0
5 V = w id e
0 V = N o r m a l
p ic t u r e w id t h .
I C 4 0 0 6 / p in
7 – D C
v o lt a g e . P u ls e w id t h c o n t r o l
In the previous stage a positive pulse is made and enters this stage from
CN1304/pin 10. This pulse resets a ramp that is applied to IC4004. IC4004
makes another pulse from this ramp and the DC voltage at pin 4. Pin 4’s
DC voltage is not fixed. It comes from the main micro IC3251/pin 55 via
IC4006.
When a wide width picture is called for, a low DC voltage from IC3251/pin
55 is applied to Q4007. The high output at its collector is input to buffer
IC4006/pin 5. Then IC4006 amplifies and inverts this voltage. The low
voltage that is output IC4006/pin 1 is applied to comparator IC4004/pin 4 to
change the pulse width.
As a result, the lower voltage at IC4004/pin 4 produces a wider positive
output pulse at IC4004/pin 2. Q4028 and Q4003 amplify the output pulse.
The pulse is low pass filtered into a DC voltage to become the supply
voltage for the horizontal driver device
A wider positive pulse produces a higher DC supply voltage. The higher
voltage increases the horizontal driver’s amplification, resulting in an in-
creased picture width.