Sony KP 48S70, Training Manual

Page: 63 / 101

xxi
VERTICAL DEFLECTION
Vertical Drive
IC301 Y/C Jungle contains a vertical oscillator whose frequency is deter-
mined by C323 which is connected to IC301/33. This oscillator is used to
create the drive signal for vertical deflection. It free-runs at approximately
60Hz to maintain a raster under no signal conditions. When a video signal
is present it is locked to the video’s vertical sync pulse which is input at
IC301/43.
IC301 Y/C Jungle uses the vertical oscillator to generate two vertical drive
signals which are output at pins 29 and 30. These signals are sawtooth
waves and are 180 degrees out of phase. They are shown in Figures 1
and 2. These signals are then input to IC1501 V Out where they are am-
plified and output to the vertical yokes. You also notice that IC301 pins 29
and 30 are input to the Vertical Zooming Amp IC1502. There they are
multiplied with a sample of the ABL signal. This is done to compensate for
vertical size changes due to lack of high voltage regulation. The outputs
from IC1502 are then summed with the vertical drive signals at Vertical
Output IC1501/1 and 7. The vertical drive signal output from pin 5 is about
55Vp-p. This is possible because IC1501 contains a voltage boost circuit.
IC1501/3 is used as a flyback supply and boost the positive supply on the
output to 45V. A sample of this pulse is used to create VP. The output
signal swings from -10V to 45V. The vertical drive signal is then sent
through L1501 to the three deflection coils via CN1501.The coils are con-
nected in series. The return path to ground for the signal is through TH1501,
R1501 and R1518. The return signal also applies negative feedback to
the input via C1524, C1502 and R1506.
Protection
Since a loss of vertical deflection will damage the CRTs, protection is pro-
vided in the event of deflection loss. Since there is no return of VP to the
Y/C Jungle we need another way to blank the set if we lose vertical deflec-
tion. Since the VP pulse does go back to System Control IC001 to control
data timing this line is used. When the VP pulse is not present at IC001
the data and clock signals between System Control and the Y/C Jungle
are incorrect. Any time there is no communication on the data bus be-
tween System Control IC001 and the Y/C Jungle IC301, System Control
cycles the power relay line pin 62 OFF and ON. Therefore any failure that
causes loss of Vertical deflection will cause the set to continuously power
OFF and ON.