Integrated Circuits - Zenith H27G48S Service Manual

SIGNALS
Three types of signals, ATSC, NTSC and
SVGA, are processed in the set. The
ATSC signals are down converted to NTSC
signals and it are processed as com-
posite video signals. The input pin,
of the A/V Switch is the pin 15.
•CV RF: The IF section sends the com-
posite video to the ICM2900 A/V switch
(CXA2089Q, I2C bus supported) at pin
47.
•CV-2: Fed from the rear jack pack to
the A/V switch at input pin 8.
•CV-4: This input, called Camport, is
fed to the A/V switch via pin 23.
•Y1-IN: This is the luminance input of
the Y/C (super video) connector and is
fed to the A/V switch through pin 3.
•C1-IN: This is the chroma part of the
Y/C (super video) connector and is fed
to the A/V switch through pin 5.
All of these signals must be input to
the A/V switch with a loaded 75ohms @ 1
V p-p level. The microprocessor se-
lects the signal through the I2C bus.
Switched composite video is sent to
the pin 53 of ICM2001 IC Micronas. This
IC has internally a 4H 3L comb filter
used to separate the luminance and
chroma components. Switched luminance
and chrominance signals are sent to
pin 55 and 56 of the ICM2001.

INTEGRATED CIRCUITS

ICM2001 (VSP9405B, I2C bus supported)
is a SCANRATE CONVERTER including CHROMA
DECODER. Package is a QFP80.. It re-
ceives luminance and chroma signals plus
composite video signal and decodes them
to YUV video with synchrony. The dia-
gram shows the connections of the lu-
minance signal to the synchrony in-
puts. This is because the chip extracts
the horizontal and vertical sync pulses
from the luminance composite sync. All
output signals are up converted to
37.9Khz
The YUV – H, V sync signals from the
ICM2001 are fed to the ICM2700 at pin
4(IN3_H) and pin 5 (IN3_V). The ICM2700
(CXA2151, I2C bus supported) is a multi-
scan and incorporates four system video
switch including H, V sync signal pro-
cessing. It has sync signal automatic
identification circuit with fixed mode.
Also, receives the H, V SYNC –SCAN (comes
from SCAN CARD) at pins 36 (IN1_H/L1)
3828VD0171G
SERVICING
and 37 (IN1_V/L2) and the H, V SYNC –
FRONT (comes from front jack pack) at
pins 44 (IN2_H/L1) and 45 (IN2_V/L2)
to be switched in itself. The ICM2200
(CXA2150Q, I2C bus supported) is a bi-
polar IC which integrates base band Y/
C signal processing, RGB processing,
Horizontal sync signal processing that
support 37.9Khz. The output of the
ICM2200 is three lines of video (RGB)
and two lines of sync (HV). The RGB
lines are connected to the ICM2702
(BA7657F) together with external RGB
computer signals come from ICM2701
(BA7657F) are switched to video output
board.
VIDEO OUTPUT BOARD
The Video Output Board is composite by
one 160Mhz Video pre-amplifier IC, three
monolithic power amplifier ICs (one for
each color signal) and one Spot Killer
circuit.
The Video pre-amplifier IC5101 receives
the RGB OSD, Fast Blanking OSD, Clock
and Data signals from the main board
through CN9C3 12-pins connector. The
main RGB signals are carried in to the
video module through the CN9C2 8-pins
connector. The ABL, CLAMP and Horizon-
tal Fly Back signals are feed to the
pre-amplifier IC through the CN9C4, 4-
pins connector.
The power supply is 8V DC –5%, +10%.
The pin 7 is the power supply for the
input stage and the pins 21,18 and 15
are the power supplies for the RGB out-
put stages.
The main functions of this IC are, Main
picture Contrast and Brightness con-
trol, OSD Contrast control, RGB Cutoff
and RGB Gain adjustments and ABL con-
trol.
The RGB input signals are capacitive
coupled by CM5109, CM5110 and CM5111
4700pF smd capacitors and actively
clamped to the internal reference black
level during signal black level. The
Input signal amplitude is 0.7V (black
to white) and should not exceed 1V. The
coupling capacitors
Also functions as storage capacitors
between clamping pulses. Very small
input currents will discharge the cou-
pling capacitors resulting in black
output signals for missing input clamp-
ing pulses. (Pin 5 CL1).
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DIGITAL FCS - SERVICING