Sony UP-960, Service Manual

Page: 34 / 94

4-4 UP-960(UC)
UP-960CE(CE)
4-1. VIDEO CIRCUIT
4-1-1. Input Trap Filter Circuit
The composite video signal is inputted to MA-91 board from BNC connector (CN1-VIDEO IN). 75 ohm termination is
turned ON/OFF by dip switch (S501 pin 1). After that, it is divided three signal systems via input buffer, the signal passed
through trap filter (FL1) for NTSC, the signal passed through trap filter (FL2) for PAL, no processed signal is inputted to
the analog switch (IC1 pins 1, 3 and 5). Selection of signal is performed by system control (IC505) and inputted to the
video amplifier 1 (IC2 pins 15 and 16).
4-1-2. Sharpness, AGC Circuit and C-SYNC Signal
The signal from analog switch (IC1) is divided two systems, one is inputted to the video amplifier 1 (IC2 pins 15 and 16),
another is inputted to the peak detection circuit for AGC. Sharpness is switched Soft and Hard by changing the voltage that
is inputted to the video amplifier 1 (IC2 pin 13). The voltage is switched by analog switch (IC5) and controlled by system
control (IC505). AGC is performed by using contrast amplifier in the video amplifier 1 (IC2). When setting AGC to ON,
the voltage is peak voltage of input video signal that is obtained by peak detection circuit (Q13, Q14, IC4), when setting
AGC to OFF, the reference voltage is outputted from analog switch (IC5) by controlling system control (IC505), both
voltages are fed back to video amplifier 1 (IC2 pin 11) and controls gain of amplifier. C-SYNC signal is outputted from
video amplifier 1 (IC2 pin 3). Peak detection circuit for AGC is also used this C-SYNC signal.
Peak Detection Circuit
4-1-3. Brightness, Contrast Control and A/D Conversion
The video signal outputted from video amplifier 1 (IC2 pin 10) is inputted to video amplifier 2 (IC6 pin 16) via low pass
filter (Q6, Q7). The voltages obtained by each volume on the front panel are inputted to video amplifier 2 (IC6 pins 4 and
6). And BRIGHTNESS and CONTRAST adjustments are performed according to this voltages. After that, adjusted signal
outputted from video amplifier 2 (IC6 pin 9) is converted to digital signal at A/D converter (IC7) and it is stored to the
memory.
C-SYNC
VIDEO
Q11, Q12
Q13
Q14
IC2
RV2 RV3
GAIN ADJUSTMENT
IC5-
!=
CLAMP
PULSE
GENERATOR
PEDESTAL
CLAMP
INTEGRATION
CIRCUIT
VIDEO
AMP