Horizontal Position Ci Rcuit; Horizontal Blanking Circuit; Pwm Signal Generator - Tatung OMNISCAN SERIES Service Manual

3.19 HORIZONTAL POSITION {RASTER)CIRCUIT
(Reter to circuit. diagram Fig-19)
Adjuft~.r~tal
raster centering' is achieve using
complementary voltage derived from secondary
winding T201 and network D206-D207-L202.
The raster's horizontal position is achieved by
selecting P202, P203, P204 on either end of the
connector, the DC voltage (lOY) produced across
R224, R225 introduces a DC element to the current in
L404 and the yoke assembly. The background raster
should be centralized with respect to the edges to the
bezel during the set up procedure.
RASTER'S HORIZONTAL POSITION CIRCUIT Fig-19
P40:; TO
P20~/'204
r:r ":1
't
0
SF.'-E(;T~~
I'"
(0;,
I
N
4 III
W 0
o.
M . RAS T F.P.
pos
IT I
os
3.20 HORIZONTAL BLANKING CIRCUIT
(Refer to circuit diagram Fig-20)
The flyback pulse on secondary winding pin 4 of
T 401 (Horizontal output transformer) not only provides
the raster width control signal but also combined with
the vertical blanking signal via 0321-0324-0322-
0323 to produce a composite blanking signal for the
video amplifier.
HORIZONTAL BLANKING CIRCUIT Fig-20
,..----...4
24V
JR365
10
r----+
! 12'N
TEST TEST
CONDITION POINT
Fh=31KHz Gl
G2
"~22
;C!6
Q
5R
I '
H/V
. .., r--i>
BL ANK I NG
~ ,..~
@
~~40
OU1 PUT
,
J.
. .
0323 16~V
TO P904
An:.,
V.8lAN!<ING
INPUT
TEST POINT NAME
H PULSE
H BLANKING
Gl 42 Vpp
I
I
1
I I I
I
I !
I i I I
I
!
I i
I
I
I
I
!
tL~-: I I
I I
I
i
I
I
j
I
I
i
I I
i
I
LL.! I I
I
I I I
I
I
LU
I I I I I I
G2 23 Vpp
I
~L,
.~
-
r-
,--
!
..
- --
.- -
FF
-
G3 23 Vpp
3.21 PWM SIGNAL GENERATOR
(Reter to circuit diagram Fig-21)
A square waveform signal is fed to 0602 via C600-
R631, a ramp Signal is generated by C603 with the
peaks being clipped to 12V by 0605. In order for the
system to function correctly, the slope of the PWM
reference signal is modified by 0601-0600.
The ramp signal is fed to pin 3 of 0606a and pin 5 of
o
606b, and used as the reference signal for the
Pulse Modulation Comparator in the horizontal and
G3 H & V BLANKING OUTPUT HV. control circuit.
=
3-17
=