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6. Video section.
The internal block diagram only for the video processing is shown in Fig. 13.
Chroma
Output Stage
3% Color gain
Control
R222
Q201
Amp
Blanking
Pulse
Composite
Video input
Pulse
G
Clam
Brightness
Control
O +12V
Fig. 13. Video section block diagram.
(1) Inverter amplifier.
The composite video signal with negative going sync is applied to Pin 39 (inverter amp) of IC501 through
Z201,Z202:(sound carrier trap), from Pin 22 of IC101. Z201 is a ceramic filter which reduce 5.5MHz beat
and 2202 is a ceramic filter which reduce 6.5MHz beat in the picture.
L202 and Z201 form a series resonant circuit tuned to 5.5MHz,6.5MHz. The trap is in shunt with the
output (load), furthermore the trap is pratically a short circuit at series resonance.
As a
result, the 6.5MHz intercarrier
sound is removed
from the composite video signal. The frequency
spectrum of this trap output is shown in Fig 14.
L201
Response
aes ;
| Equivalent
jcircuit of
I
2201
Iceramic filter
I
I
|
|
I
11
|
|
!
5.5MHz
6.5MHz
}
L
Fig 14. ceramic filter.
Pin 39 is the input terminal, and the operating bias is derived from the DC component of the PIF output.
The input dynamic range of Pin 39 is 2.0V to 6.5V typ. Pin 39 is also the input terminal of the contrast
amplifier. The output terminal of the inverter amplifier is Pin 40, and the output circuit is emitter follower
construction to increase the driving capability. This inverted video output signal is
split into two paths,
one to the sync seperator (R226, R227, R218, C254, C205, C206, D202, Pin 37), and the other to the
chroma bandpass amplifier (Pin 5) through a chroma signal taking out circuit (R205, R204, R290, C204,
C202, L202). The typical gain of the inverter amplifier is 3.5dB.
31
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