PHILIPS LX3700D/21S
Service Manual

11-25

11-25

In normal mode when Tuned is going �High� the channel data should be transmitted to the synthesizer to protect the receiver in case of hang-up situations.
3740
+5V

F740
6751
F740

+10V

3766 820R

F741

7750 PIC12C508A 7 6 5 4

DA CL

3750 1K0 3749

F742

3753 4u7 35V

F742

8 3 2754

1K0

F741

POWERSAVE MUTE
6710 BAV70

STEREO

TUNED

3 2

GP0 CTRL GP1 T0CKI MCLR VPP OSC2 OSC1 CLKIN GP<0:5>

10 5

Muting The mute of the receiver is controlled by the IF receiver part but can be overiden by the microcontroller. The mute action initiated by the microcontroller is necessary during channel switching and in the standby mode. Muting has priority on all other main tasks. The hardware Mute is the result of an AND function between the �Tuned� and �Stereo� information. The Tuned information can be read by the microcontroller ( pin 2). The same pin (pin 2) has to be put in output mode to activate the microcontroller initiated Mute. This Mute must be used during the frequency setting and during the standby mode. Powersave mode
MUTE
CL36532008_086.eps 290403

DC-references and supply: +/- 15 Vdc preamp supply: The supply for the preamp is made by using a derived +/-15 Vdc from main power supply +/- 29.5 Vdc. Doing so assures a good symmetrical start-up on the power lines of the preamp, this suppresses possible plops.This supply is 15V for all operating conditions, except power save standby.

+/- 29.5 Vdc main supply: Will be switched off when the unit goes into power save-mode. See circuitry around 7107 and 7106. + 10Vdc receiver supply: Is always present, receiver stays always active Note that all supplies have the same ground reference.

100K BZX384-C5V1

BAS316

Mute circuitry: In normal operating circumstances, the voltage on the- �mode� pin of the amplifier IC7101 will be 4V5. This is the MUTE_AMPn signal.
+10V +10V

7 2

9 4 1K0

6752

F743
F743

8 1

F744
F744

+5V
3798 22K

6109

1765 SKR 14 12
11

3149
3150 100K MUTE_AMPn 3155 2K2

6110
2K2 LTL-1CHGE
F124 7109 BC847B 7110 BC847B STBY_OUT

13

{POWERSAVE,MUTE}

Figure 1-26 Microcontroller functions

BZX79-C5V1 3147 MUST BE BZX79-C5V

The main supply can be switched off with the �powersave� control line to reduce the current consumption. The microcontroller is always powered by the power supply. All other electronics can be put into powersave mode. After approx. 10 minutes of no �Tuned� signal the receiver goes into powersave mode. Once in powersave mode, the receiver is operated in �listen-sleep� mode to reduce the average current consumption. Power supply The board is having a low drop voltage regulator 7790, which has an output voltage of 8 Vdc. The 5 V supply for the micro controller is extracted from the 10 Vdc input supply via a zenerdiode 6751. The 5 Vdc supply of the synthesizer is extracted from transistor 7606. The powersave signal is also provided to the connector for the amplifier and for AV via the amplifierboard the SMPS is controlled.

6 1

+10V 3151 47K

6100 3133 47K BAS316 7104 BC847B

F127

MUTE_RX

7112 BC847B 3153 10K +10V +10V

Frequency setting Frequency setting is necessary when the 4-position slide switch is changed. In an internal look-up table the 4 required frequencies for the local oscillator are stored. The output towards the synthesiser chip in the frontend is in I²C form. The synthesizer is the only device on the bus. During frequency setting the Mute is active. Scanning of the channel switch should occur within every 250 milliseconds in any mode.

6101

3138

3140

2K2

3141 22K STANDBY 6105 BAS316 3142 10K 3143 47K 7107 BC847B

7106 BC847B

The AV-version of RX Amplifier board
3146 MUTE_WIRED

General: The amplifier module is intended to deliver 2 x 50 Watts into 8 ohm speakers. Speakers are connected through �easy-fit� connectors. See amplifier blockdiagram.
W
AUDIO OUTPUT AMPLIFIER +10V

10K

7108 BC847B

10u

BZX79-C2V7 BAS316

16V

2152

560K

6106 6103

10K 3148

OPTION

CL36532008_108.eps 290403

+ Analog sensitivity 1.4Vrms 7100-D,7100-A F111

1106 1 2 3 4 5 6 7

3144 F135 F137 F138 F139 +10V F140 F142 F144 3117 (active high) MUTE POWERSAFE (active high) sensitivity 2.5Vrms L R

7101 TDA8920 Input

+ Power

Figure 1-28 Mute ampn circuit
5104,2122 Driver F113 F112 1100 4 3 2 1 8 Ohm/50W 8 Ohm/50W

F114

Input

Driver

F115 F117

This signal is coming from zener 6101 via diode 6100. Transistor 7104 and 7107 are not saturated at that moment. When the receiver generates a �mute� (MUTE_RX = 4Vdc on pin 6 of connector 1106) then 7104 saturates, diode 6100 blocks and the level on pin 6 -of IC 7101 becomes 2V1. The signal is now formed by zener 6106 via diode 6103. All DC references stay as they were; the class D keeps on oscillating, the led stays green but no sound is produced on the outputs. The control line STBY_OUT (connector 1107-pin 3) to the power supply stays low. When the receiver goes into powersavemode (= after 10 minutes no signal from the AV set), STANDBY signal is high; then the circuitry around 7107 pulls down the mode line of the amplifier to nearly 0V via the MUTE_AMPn signal. (Note that the mute line from the receiver is also high under this condition). The amplifier is completely in standby mode, the oscillator in amplifier IC 7101 stops and all internal references are disabled. The led red will be on, while green is off. At the same moment transistor 7106 is not saturated anymore and the control line towards the switched mode power-supply becomes high. This switches off the main +/- 29.5Vdc supply and the whole unit comes in a real power save mode. 7112 helps to pull down the
6108 3135 BAS316 560K 3129 2K2 6107 BAS316

mute line of the amplifier-chip 7101 as fast as possible to avoid plops at this transition. When the receiver detects a valid signal from the AV set, this power-save-line becomes continuously low, and after a small time (2152, 3143, 3147), 7104 is off. At the same moment the mute line becomes low and the amplifier is enabled again. Also the control line (connector 1107-pin 3) to the power supply becomes low, thus starting up the main +/- 29.5 Vdc supply Amplifier The amplifier TDA8920TH operates on +/-29.5 Vdc and can deliver 2 x 50 Watts into 8 ohm loads. Using the very efficient class D - technology, it minimizes the dissipation. The class - D chip runs on a ± 300kHz oscillator, therefore a 12dB / octave output filter is needed (coil 5104 and 5105, and capacitor 2122 and 2125). Input signals are 180° phase shifted by 7100-C and 7100-D, ( the effect - speakers have to be in phase with left and right main speakers, otherwise bass reproduction will be poor) Input signals are filtered in the two-section high pass filter around 7100-B and 7100-A. The � 3 dB point is somewhere around 30Hz. Input sensitivity of the amplifier for maximum output: typical 1.4V rms

3126 7104 MUTE CONTROL

7100-C,7100-B Temperature protection 6100 6101 C5V1 7105,7108 WIRED MUTE DRiVER 7107 POWER SAFE CONTROL 6106 C2V7 7110 +29,5V "+Power" "ON" LED DRIVER F124 GREEN 6109 6103 MUTE_AMPn F127 Mode mute OSC

5105,2125

- Power

- Analog

WIRED AUDIO IN (3,5MM stereo jack)

1109

F120

1 3 2 5 R L F122

F121 F125 MUTE WIRED F110 F128

7109 "STANDBY" LED DRIVER F123 RED 6110

7106 STANDBY DRIVER

1104 1 From SMPS Conn. J2 2 3 4 F134 F136 F129

+ Analog +15V

+10V -15V F141 - Analog F119 -29,5V "-Power" 1 2 3

Standby out

F143 F145

1107 From SMPS Conn. J3

update mdi 13-03-03

Figure 1-27 Block diagram amplifier The crossover of the built-in high pass � filter will be around 30Hz. This eliminates sub-bass info going to the surround speakers. The amplifier uses �class D� amplifier-chip TDA8920. Additionally, the module is featured with a 2-colour indicator, green indicates the active state while red is standby. There is also an on-board 10 Vdc supply conditioning, specially intended for the TX receiver.

2K2 LTL-1CHPE
F123