Philips LC03E Service Manual page 109

Circuit Descriptions, Abbreviation List, and IC Data Sheets
9.8.1
Introduction
All sets contain one of ITT's Multistandard Sound Processing
ICs for sound decoding:
•
MSP3410 (or 3411): Multi System (incl. NICAM) decoding
for Europe and AP (Virtual Dolby).
•
MSP3421 (or 3421): BTSC decoding for NAFTA and
LATAM (Virtual Dolby).
This IC takes care of the main FM, AM and NICAM sound
decoding.
The analogue input and output sections of MSP offer wide
range of switching facilities such that it is possible to distribute
all possible source signals (internal and external) to the desired
output channels (main, headphone or SCART outputs).
All MSP versions contain digital audio processing, used for the
basic left/right stereo sound, such as bass, treble, balance,
incredible sound and spatial and source selection (SIF-signal,
EXT1 or EXT2).
In addition to that, the MSP34x1 versions are also able to
perform Virtual Dolby, a Dolby approved sound mode for
surround sound reproduction with left/right speakers only.
9.8.2
Source Selection
Table 9-1 MSP Overview
Micronas IC System
MSP3410G Multi-system No
MSP3411G Multi-system Yes
MSP3420G BTSC
MSP3421G BTSC
The above-mentioned Micronas ICs are all having four pairs (L/
R) of SCART audio inputs. The fourth input pair (AV4) is used
as audio-in (input cinches located at the Scaler board) for PC
and HD modes.
To get a constant level output if the Tuner is selected, the
SCART1 output (Tuner at any time) has to be fed back to the
input selector and selected as input for the MSP (SCART1
input).
9.8.3
Audio decoding
At the input, a choice can be made between two IF-signals; SIF
and SIFM.
The selected signal is fed to the AGC. After this, an ADC
converts the IF-signal to digital.
This digital signal can be processed by two demodulation
channels. The first one is able to handle FM and NICAM
signals. The second one can handle FM and AM signals.
Each channel contains a mixer to shift the incoming signal in
the frequency domain. This shift is determined by the value of
a DCO (Digital Controlled Oscillator).
After the down-mix, the signal is fed, via a filter, to a
discriminator. From here the AM, FM or NICAM demodulation
can be performed.
Both channels contain an 'automatic carrier mute' function,
which automatically mutes the output of the analogue section
when no carrier is detected.
After demodulation, the FM-signals are subjected to a de-
emphasis operation. After that, the matrix of the stereo system
is applied.
9.8.4
Audio Processing
The sound processing is completely done by the MSP34xx:
•
Volume control is done by the user via the SOUND menu.
•
Tone control in 'Stereo' sets is done via the BASS/
TREBLE control.
•
Headphone control in 'Stereo'-sets is done via the
loudspeaker output of the amplifier. In 'Virtual Dolby'-sets,
Virtual Dolby Region
Europe/AP
Europe/AP
No Nafta/Latam
Yes Nafta/Latam
LC03E
the MSP has a separate Headphone output so separate
sound control is possible.
•
Mute control can be done in different ways:
–
System muting. System muting is implemented for
"special events" such as channel/source change event,
loss of identification signal, on/off of set, during search
and auto store/program, sound mode change. This
muting is transparent to the user. Audio output should
be muted before the above "special events" occurred,
to prevent problems such as audible plop. Muting is
done via the SOUND-ENABLE line (active "low")
connected to the amplifier-IC and coming from the
Painter.
–
Headphone status mute. A headphone status is
available to detect the presence of the headphone and
mute the main speakers if the headphone is detected.
The microprocessor will read the HP-SIDE-DETECT
status.
–
User muting. This is a mute option available to the
user. The user select the MUTE option on the remote
control to switched off/on the sound output to the main
loudspeaker and the subwoofer.
Automatic Volume Levelling (AVL)
One of the features of the MSP-family is AVL. If used, it limits
the big volume differences in the broadcast between e.g. news
transmissions and commercials or within a movie.
To be able to get a Dolby approval (for the Virtual Dolby sets),
the AVL feature must be switchable. Therefore, the AVL
feature is customer switchable via the menu.
9.8.5
Audio Amplification (Diagram A9)
Some specifications:
•
15" and 17" models: 2 x 3 W with power amplifier
AN7522N.
•
23" models: 2 x 5 W with power amplifier AN5277N.
•
All models are equipped with a subwoofer output.
The audio output stage is built around IC7731, which is a
balanced amplifier, and is located on the TV board. It uses an
monolithic integrated power amplifier IC, the AN5277. The gain
of the amplifier is constant. This means that volume control has
to be done via the MSP.
The supply voltage is 12 V/24 V depended on screen size,
generated by the power supply via L5733
The AN5277 delivers an output of 2 x 10 W_RMS to two full
range speakers. A subwoofer is not implemented.
Headphone Amplifier
The headphone outputs are from the same audio power
amplifier. The headphone jack will disconnect the audio output
to the speakers when a headphone plug is inserted. Hence, the
speakers are muted if a headphone is connected.
Protection
This two resistors are to limit the audio output to HP.
9.8.6
Audio: Lip Sync
A "lip sync" circuit with an 80 ms audio delay is added, in order
to synchronise with video delay due to the complexity of the
display processing. See table:
Table 9-2 Lip sync overview
Speaker Monitor
Input out(delay) out(delay)
AV1 AV1 (80 ms) AV1 (80 ms) RF (none) AV1 (80 ms)
AV2 AV2 (80 ms) AV2 (80 ms) RF (none) RF (none)
AV3 AV3 (80 ms) AV3 (80 ms) RF (none) AV3 (80 ms)
9. EN 109
SCART1 SCART2
out(delay) out(delay)