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1. Video System
1- 1 Video amplifier circuit
The analog video RGB signals are input from pins 1, 2 and 3 of 0-SUB 15-pin connector, and they
are controlled by voltages at pins 1, 4, 8, 12 and 14 of CN-C1 connector. The video gain is adjusted
with VR701 to VR703 so that 40Vp-p is obtained with Contrast Control in MAX position, or 10Vp-p
in MIN position when 0.7Vp-p is input.
1-2 Synchronous separating circuit
In the case of CSNC. ON GREEN analog signal, the GREEN signal is input to CN-C1 pin 3, then
only sync. signal is taken out by the circuit consisting of 0822 and 0812 to 0814. In this case,
IC802 pin 6 is "L'', and 0815 and 0817 are in O F F state.
The sync. signal is input to IC802 pin 12 to generate the clamp pulses. On the other hand, it passes
through 0816 and 0818, and is output as horizontal sync. signal. Then, horizontal component is
removed by RC integration circuit consisting o
0819 to 0821 to output vertical sync.
in ON state, 0816 collector goes low.
1-3 Clamp
circuit
The clamp circuit, which determines
on the
H.
SYNC. signal. The clamp pulses are input to IC701 pin 15. The clamp pulse circuit
changes the phase of pulses to be generated depending on SYNC. ON GREEN signal or
SEPARATE signal.
•
In the case of SYNC. ON GREEN signal
H.
SYNC. signal is input to pin
result, the phase is delayed.
f
•
In the case o
SEPARATE signal
The pin
12
goes low, and negative H. SYNC. signal is input to IC802 pin
same phase are output
1-4
Brightness
and contrast control circuits
The brightness control varies
varies SUB
BR IGHT
terminals (pins
base voltage of
0706,
then the voltage of
gain becomes larger
as
1-5 Automatic brightness limiter (ABL)
The ABL circuit works when CRT anode current exceeds about 300µA. when anode current is
below 300µA, the voltage of CN-C5 pin 7 is clamped to 12.6V by 0711. When anode current
exceeds 300µA. the voltage of CN-C5 pin 7 drops. Then, 0708 and 0707 are turned on, and IC701
pin 14 potential drops. Consequently, the video output becomes smaller.
CIRCUIT DESCRIPTION
f
R836, R837, C807 and C808, then passes through
signal.
In the case of SEPARATE signal, 0815 and 0817 are
a
black level of video signal, generates clamp pulses based
12.
The 0803 base goes low and IC802 pin 11 goes high. As a
from pin 9.
of CRT.
voltnge
G1 Grid
19, 24
and 29) of
I C701
pin
14
IC701 pin
voltage is higher.
14
circuit
-31-
11.
Then, pulses of
Also, in order to attain white balance, it
IC701.
For the contrast, VA? A 1 varies the
vnries. As a result, the video gain varies. The
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