Toshiba TW40F80 - Manual (Page 49)

49
4-3. Main/Sub Screen Superimposing Section
In normal mode (with only the main screen picture displayed),
the YS signal voltage always goes low and the Y, I and Q
signals from the digital unit are developed at pins 15, 4 and
14 of QY48.
The Y, I and Q signals for the main/sub screens superim-
posed are developed at pins Y05, Y06 and Y04 of PY01 and
then supplied to the receive circuit.
The Y, I and Q signals for the main/sub screens superim-
posed inside the receive circuit are entered to pins 53, 51 and
52 of Q501 (TA1222N) and then fed to CRT. The video
signal is processed in Q501 without distinguishing the sig-
nals for main and sub screens, so the high picture quality can
be obtained equally for both the screens.
CY231
CY230
CY232
CY239
CY240
CY238
Y
I
Q
YS
YD
ID
QD
SCP
3
2
1
4
Clump capacitor
Clump capacitor
3
9
1
4
8
2
Analog
SW
5 6 13
QY46
TC74HC4066AF
Analog
SW
QY47
TC74HC4066AF
5 6 13
3
9
1
4
8
2
Waveform
shape
Clump
pulse
Constant voltage
source E
From Sub screen process section
Signal reception circuit
Signal reception circuit
QY48 MC74HC4053
1 IY (Y IN)
3 IZ (I IN)
13 IX (Q IN)
11 A
10 B
9 C
2 OY (Y IN)
5 OZ (I IN)
12 OX (Q IN)
15 Y COM (Y OUT)
4 Z -COM (I OUT)
14 X-COM (Q OUT)
Y05
Y06
Y04
53
51
52
43
42
41
R
G
B
Y
I
Q
YOUT
I
Q
PY01
Q501
To CRT
Main/Sub picture
superimpose
PY02
TA1222N
Fig. 6-4 Main/Sub screen superimposing section
The main/sub screen superimposing section is shown in Fig.
6-4.
The sub screen Y, I and Q signals sent from the sub screen
process section and the main screen Y, I and Q signals sent
from the digital unit through the receive circuit and etnered
pins 3, 2, and 1 of PY02 are clamped at a same electrical
potential and the former are fed to pins 1, 3, 13 and the latter
fed to pins 2, 5 and 12 of QY48.
The clamp circuit contains a clamp pulse waveshaping SCP
at pin 4 of PY02, analog switches for ever-voltage source E,
QY46 and QY47 and clamp capacitors CY230 ~ CY232,
CY238 ~ CY240.
QY48 is an analog switch to feed the Y, I and Q signals for
either sub screen or main screen to pins 15, 4 and 14 by the
YS signal voltage fed to pins 9, 10 and 11. When the YS
signal develops high, QY48 selects the signals for the sub
screen and when low, QY48 selects the signals for the main
screen. Consequently, the signals for both the main and sub
screens are superimposed each other.