Hitachi CP2896TA, Руководство по обслуживанию

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21
OPTIONS
Active Subwoofer
Comb Filter
CF700
SVM module
Audio Feature
AR700
Audio Feature AR701
Adjustable Audio TA700
Scart 3 + VGA-audio TA710
Scart 3 TA711
Picture in Picture PP700 / 710
Active Subwoofer
General
The active subwoofer system provides a clear improve-
ment in stereo sound. The system consists of active filters,
power amplifiers, a subwoofer, and stereo speakers. The
active subwoofer stage is designed to be used with an in-
ternal subwoofer box and stereo speakers in the TV set or
with small external front speakers.
Functional description
The left and right stereo channels are already added to-
gether in the sound processor MSP3410D. The sound proc-
essor also includes the required lowpass filters for the
subwoofer channel and highpass filters for the loudspeaker
channels.
The signal is taken from sound processor pin 31 and fed
onward to the high pass filter (40 Hz), consisting of transis-
tor ta6 and associated components.
The filtered signal is then fed to the audio power amplifier,
ICa4. The amplifier can be muted by pulling pin 2 low. The
mute control signal is taken from microcontroller (pin 51)
via transistors ta10, ta4 and ta5. This mute function mutes
each of the audio power amplifiers in the set. However,
the subwoofer amplifier can also be muted separately. This
can be done via the audio processor. A high level on pin 5
drives transistor ta5 to conduct, which just mutes the
subwoofer amplifier. Due to the resistor network ra106,
ra105 and ra14, the central mute will be not activated in
this case.
The amplifier operates in a bridge configuration. The out-
puts are internally inverse feedback connected to the in-
puts of each other. The amplified, phase opposition sig-
nals are output from pins 4 and 6 to the subwoofer speaker.
Comb Filter module, CF700
General
The basic function of the comb filter is to separate the lu-
minance (Y) and chrominance (C) signals from the CVBS
signal. The device minimizes problems caused during Y /
C separation such as dot-crawl and cross colour interfer-
ence. In addition, it allows the input video signal to have
an extended frequency bandwidth. This is carried out us-
ing a clock frequency of four times the colour subcarrier
frequency. The filter is capable of handling signals accord-
ing to the PAL and NTSC 3.58 standards. The module con-
tains two ICs, the multiplexer circuit, icc1 and the comb
filter circuit, icc2.
Functional description
Depending on the standard, the module either bypasses
or filters the input signal as follows:
PAL and NTSC 3.58
The signal is fed to comb filter IC and separated
for Y and C signals
NTSC 4.43 and SECAM
The signal is fed to comb filter IC, but it is not sepa-
rated
S-VHS The signal is bypassed in the multiplexer IC
The standard is identified in the colour decoder Icd1. The
standard information is input to the microcontroller via the
IIC-bus and back to the colour decoder again. The infor-
mation is output from pin 23 to comb filter module pin 1,
from pin 16 to module pin 2, and from pin 15 to module
pin 13.
Module pin 1 controls the multiplexer to bypass the video
signal (“L”) or to feed the signal to the comb filter IC (“H”).
When pin 1 is high, it inputs the colour subcarrier frequency
(Fsc) to an internal clock generator of the comb filter IC.
Module pin 2 defines the comb filtering method, PAL (“L”)
or NTSC 3.58 (“H”).
Module pin 13 drives the comb filter IC to be in comb filter-
ing mode (“H”), at which time the IC performs Y / C sepa-
ration. Or to be in a bypass mode (“L”), whereat the signal
is not separated, but fed only via an internal delay stage.
In addition, pin 13 informs the colour decoder the exist-
ence of the module by transistor tc3 (base-collector joint).
Depending on which standard is in use, the logical high /
low level combinations are as follows:
Standard module module module
pin 1 pin 2 pin 13
PAL “H“ + 4.43 “L” “H“
NTSC 3.58 “H“ + 3.58 “H“ “H“
NTSC 4.43 “H“ + 4.43 “L” “L”
SECAM “H“ + 4.28 “L” “L”
S-VHS “L” “L” “L”