RCA HDLP50W 151 - AUDIO SWITCHING OVERVIEW - AUDIO PROCESSING - VIDEO SWITCHING
AUDIO SECTION
The A/V In/Out circuit board is broken down into it’s two
(2) basic functions; these are audio switching and video switching. The audio
switching circuitry for the external audio inputs are located on the A/V In/Out
module. Source selection for DVI audio and the analog external audio inputs
including FAV audio jacks is provided by the audio switching IC U26901. The
audio switching is controlled via the I2C RUN 1 bus from the DM2CR module. Also
the DM2CR module performs demodulation of the audio from off-air sources (NTSC
and ATSC). These off air base band audio sources from the DM2CR are routed
through the A/V In/Out circuit board to the Audio board for final processing.
The external audio input jacks are located on the A/V In/Out circuit board. L/R
inputs include audio from Aux1, Aux2, Aux3, Aux4 and DVI. The Front Audio Video
(FAV) panel has one set of L/R audio jacks that is applied to the switching IC U26901.
The selected base band audio signal output from U26901 is looped through the
DM2CR module and back to the A/V In/Out CBA where it then sent to the audio
processing circuit board. The FAV
Headphone L/R audio from the Audio board is simply routed through the A/V
In/Out board to the FAV. When the DVI
audio input is selected it is routed to the DM2CR for decoding into analog
audio and is then routed back through the I/V In/Out CBA and on to the Audio
circuit board for final processing. Power supplies for the A/V In/Out board
include the +12VR, +12VS and +5Vr and is supplied by the AC In CBA.
AV IN/OUT CBA [SERVICE POSITION]
AUDIO PROCESSING
All of the audio circuitry is located on three
assemblies. The audio switching and the
audio jacks are located on the A/V In/Out CBA. The DM2CR module performs demodulation of the audio from off-air
sources (NTSC and ATSC). The Audio
circuit board performs the base-band audio processing such as volume control,
graphic equalizer, sub-woofer output, and power amplification along with speaker
switching. The audio circuit board also contains the SRS and Tru-Surround feature
processing circuitry.
The analogue audio from the DM2CR is routed back to the A/V
IN/OUT board where it is cabled to the Audio board. There it is input
to a differential amplifier, U11551. This amp is used to eliminate
ground loops caused by
the long cable routing. The output of U11551 is fed to the input of the
SRS/FOCUS processing
blocks, U11701 & U11702, and directly to one input of
the audio processor, U11801. The processor selects one of three inputs, the
direct signal (no SRS) from U11551, Regular SRS or Tru-Surround from U11701 or SRS/FOCUS
from a combination of U11701 and U11702.
The analogue input for the SRS/Tru-Surround circuit is taken
off the output of the amplifier, U11551. These produce two signals, which are
sent to inputs on the audio processing IC, U11801, along with the direct
signal. The processor IC selects which
input signal is required for the customer-selected mode. The first block, composed of IC U11701, performs either Regular SRS or
Tru-Surround. The second block,
composed of IC U11702 performs “Focus” mode.
Using the midpoint of the output of the SRS block and placing it in
Regular mode select regular SRS mode. Focus
is always on but its output isn’t selected. SRS Focus mode is composed of
Regular SRS plus Focus. The SRS block
is placed in Regular mode and the Focus output is also selected.
Placing the SRS block in Tru-Surround mode and
using its output select tru-Surround mode. The audio processor (U11801) has
three input signals applied to the selector, direct audio from U11551, SRS from
U11701 and Focus from U11702. After the signal is selected in the processor, volume
control is applied. The DLP system does not have a separate tone control
function but a 7-band graphic equalizer is available. After the equalizer, L
and R signals are summed and split off to form two signal paths. The summation
stage output signals are run through a high pass filter for the main channels,
and a matching low pass filter for the sub-woofer The main volume therefore
controls the sub-woofer volume, but a fader is provided in the sub-woofer path
(accessed by the “Sub-woofer Level” menu) so that it’s level may be adjusted
relative to the main channels. Three analogue outputs from the processor provide
the Left, Right, and sub-woofer signals.
The PA_L and PA_R audio signals from the audio processor are
routed to three circuit areas, first to U11460, which drives the Hi-Fi Output
jacks located on the Audio module, second to the main power amplifier, U11901
and third to the headphone amplifier, U11490.
The output of U11490 is routed through the A/V IN/OUT module
to the headphone jack, which is located on the FAV module. The sub-woofer output
from the processor is routed to connector, J11801. The sub-woofer amplifier
module plugs into this connector. Also present on the connector are two control
lines that sense the presence of the sub-woofer option and turn the amplifier
and power supply off and on.
As mentioned previously the Audio module also
contains a bus expander,11501, that is connected to the system microcomputer in
DM2CR via the I2C bus. The bus expander on the Audio Module uses its ports to
select the following functions, FAV Speaker Mute, Sub-Woofer Control, Sub-Woofer
Detect and Power Amp Mute.
AUDIO PROCESSING CBA [SERVICE POSITION]
VIDEO SWITCHING
The A/V In/Out circuit board is broken down into it’s two
(2) basic functions, video switching and audio switching. The A/V In/Out circuit board has external input jacks that accepts four Composite Video (CV),
two S-Video, two component video (YPrPb) and one DVI digital video. The video
inputs on the A/V In/Out board can be either 1H NTSC, 2H NTSC or 2.14H NTSC. The Front A/V (FAV) panel has
one component video input as well as a S-Video connector which is routed
through the A/V In/Out CBA.
The A/V In/Out CBA also has a DVI input. DVI
(Digital Video Interface) combined with HDCP (Hi-Bandwidth Digital Copy
Protection) creates a new uncompressed protected digital interface (called
DVI-HDTV) for hooking an HD Monitor to a Video Source (for example, a set-top
box or DVD player). This interface is not only uncompressed, but it is also
high speed (3.96 GB/s) making it a perfect solution when the best picture
quality and minimal signal loss are required.
A/V IN/OUT CBA [SERVICE POSITION]
The DVI receiver IC U22201 decodes the DVI video
and then outputs RGB with horizontal and vertical sync. This signal is then
applied to U28901 for switching and matrix conversion to YPrPb. This YPrPb
video is then routed directly to the Formatter circuit board. The switching for NTSC/1H sources (composite,
S-Video, and component) is provided by IC U26901 for rear input jacks and the
FAV jacks. All video switching IC’s are monitored and controlled via the I2C
bus.
A frame comb filter is provided to optimally
comb any composite source into an S-Video (Y/C) output source which is routed
back into U26901. All composite and luma inputs to U26901 have sync detectors
that are readable via the I2C bus which
allows for automatic source detection. Source selection for HD/2H/2.14H sources
(component and DVI) are provided for rear inputs (2 component and 1 DVI) with
the IC U28901. This IC is a 4-input video switch with signal format detection.
