Philips LX3950W/01 Service Manual Download Page 71

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11-21

SUPPLY

UNIT

14VDC

1100

F001

7100

1125

WIRED

AUDIO

(3,5MM

stereo

jack)

1110

"ON"

LED

DRIVER

5115

1120

5120

+12V

update mdi 14-03-03

7140

6140

SCL

SDA

SCL

SDA

I C

Control

Channel

Switch

Selection

1130

7145

+5V

F022

Audio
Detector

+5V

From
LX3750W

5100

3102
3103

3104
3105

3148

560k

3152

330k

3109

3110

3112

3111

7115

NJM4560M

Audio Notch

Filter

L4931CDT120

HT7550

7105

+12V

+5V

TRANSMITTER INTERFACE

7130,7101,6130

Power Supply

PIC12C508A

4 positions

F002

F008

F007

F003

F004

F005

F006

F010

F009

F011

F012

F013

F014

F019

F020

F016

F017

F021

F018

TRIG

F015

3126

3125

1.8

Circuit descriptions

The Circuit description of the wireless surround system.
The complete Wireless surround system consists of:
transmitter part Tx: interface-board and transmitter board
receiver part RX: receiver board, amplifier board and
SMPSupply part

Loudspeaker boxes, per equipment defined.
The interface board can be part of a TV set (EM6E-chassis)
or a separate board in the transimitter part in case of the AV
Entertainment (DVD-receiver) application.
transmitter and receiver are described as one system,
amplifier board is per application (TV or AV) adapted.

1.8.1.

Transmitter Interface board:

General

The transmitter interface (TX-interface) is intended to deliver all
necessary audio and I²C control signals to the transmitter. The
interface is capable to deliver the specific I²C protocols for the
selection of the 4 channels, the power-up and power down
sequence. Also an audio detector and a led control circuit is on
the board, all controlled by the processor. The used
microcontroller is a PIC12C508A. There is only one software
version, which can handle automatically the 2 possible TX
frequencies (864 and 914 MHz) in AV application. For TV
application the interface function is integrated in the corre-
sponding TV set and controls via I²C commands the 2
frequences (433 and 864 MHz).
Besides the I²C, all audioconditiong is done by a dual opamp
NJM4560M.
A 23 kHz pilot notch filter is formed by both coils 5115 and
5120, this to avoid interference with the used pilot of the TX.
The AV interface transmitter combination has always to be
used with the recommended mains power adaptor of 14Vdc/
150mA. (There is a EUR, UK and USA version)
Input / output - sense. :
Full modulation of the TX transmitter: on both right and left out
(pin 1 and 3 of connector 1120), 0.42V rms (or 1.1653V peak
to peak), this means for the AV interface: 20 Vrms input on right
and left input. For TV 3V rms input on right and left input.
Start modulation:
At power-up: auto start of the interface and TX transmitter for at
least 4 minutes; when no audio on one of the inputs >0.1 V for
a period of 4 minutes then the Processor shuts down the
modulation of the TX transmitter (LED off)
Tx in off mode: (TX transmitter powered, no modulation and
LED off) Start of the modulation and LED on by applying
minimum 0.1Vrms on left or right input

Frequency response: Response is flat (+/- 1.5dB) between
100Hz and 15kHz for both channels
One channel-input is built up by using an audiotrafo to make
the coupling towards source (LX3750 Home cinema DVD
player with incorporated class D amplifiers) This causes a
difference in f-response especially for low frequencies below
100Hz for left and right channel, however not audible in its
application.
Input impedance: < 1 K ohm
Led-functionality: built in led indication: Red = ON, power on,
transmitter active
Red = OFF, power on, no modulation

Audio-input section:

The right audio input channel is different from the left input:
left uses a low cost audio transfo, since there has to be a
complete separation between the left and right speaker outs
of the DVD player LX3750. Of course this gives a small
difference in frequency response, but absolutely not audible
in its application. Pin 4 is connected straight to one output
pin of the DVD speaker out: this to have a “reference -
ground”. Input impedance for both channels is always below
1Khz, making the unit immune for all kinds of interferences
on the speaker lines. The rather high input levels (up to 20V
rms /each channel) are conditioned and brought to a level of
nominal 0.42 Vrms on pin 1 and 3 of 1120. This 0.42 Vrms
gives 50Khz FM deviation in the transmitter.
Extra protection is established by the fast diodes 6142 and
6144. DC-reference is made by 3115-3116 and 2116. A
23Khz notch filter 5115 / 5120 is built in to avoid interfer-
ences with the used pilot frequency of the transmitter.

Audio detector:

A part of the audio info is fed to the audio detector built up around
7101-A and 7101-B. Basically it’s a two-stage amplifier with a
very high gain factor (3135/3133 and 3136/3134). A square signal
has to be found on the output of 7101-A. This block-wave is fed
to the rectifier/ integrator around 6130. In normal operation 7135
is always conducting, pulling down the level on the trig-input of
the microprocessor 7145. As long this input is low the connected
transmitter is enabled by the microprocessor. When no audio
input, the trig input comes high (5V), and the internal timer of the
processor counts down till 4 minutes have past away. After this
four minutes (approx.) the transmitter will be disabled = no
modulation and red led off.
A very low audio input “trigs” the processor and the transmitter
starts up again. (Led = red). Four-channel selection is done by 2
lines (LSB - MSB) on the processor.

Power supply:

The unit operates on a 14 Vdc mains power adaptor: 12Vdc,
mainly for the transmitter, is furnished by 7100 -L4931CDT120,
which is a low drop regulator. The 5 Vdc for the PIC is made by
the HT7550 low power regulator.

1.8.2.

Wireless System

GENERAL INTRODUCTION

The wireless system is intended for stereo sound in the range
from 20 Hz to 20 kHz.
It can be used for normal L/R stereo sound or for the surround
channels in Dolby systems.
The system has an analogue sound processing system
(companding – expanding) and uses synthesised tuning at both
the transmitter and receiver side. There are frequency executions

available in different frequency bands: 433 MHz (some EU),
864 MHz (EU) and 914 MHz (US).
In each particular frequency band, there is a choice between 4
different channels or frequencies.

SYSTEM CONSIDERATIONS

The Wireless system uses a very high performance audio
processing that allows up to 100 dB dynamic range to be
transmitted over a classic analogue link. Through the
companding effect at the transmitter (reducing the dynamic
range by a factor of 2 in dB) and by an expanding effect in the
receiver (increasing the dynamic range by a factor of 2 in dB).
In addition the system has the possibility to maintain the high S/
N up to low RX fieldstrengths by applying sliding stereo (this
means reducing the stereo effect at low signal fieldstrengths)
Pre-emphasis (at TX) / de-emphasis (at RX) technique is
with15 µS time constance.
Since the signal processing is analogue, there is a low latency
in the system of < 15 µS between input TX and output RX.
The receiver part has a power save mode that will be initiated
automatically when no signal to reduce power consumption.
The system uses normal FM modulation / demodulation and
also uses the Zenith stereo principle. However, the frequencies
used are different in this respect: Subcarrier freq. = 3 * 15625
Hz = 46.875 kHz (chosen because interference zero-beats with
the TV line freq). Consequently the pilot freq. is 23.4375 kHz
(half of subcarrier).