Philips LX3700D Service Manual page 85

+5V
F740
+10V 3766
F740
820R
7750
F741
PIC12C508A
DA
F741
1K0
7
F742 GP0 CTRL
6
3750
CL GP1
5
F742 T0CKI
1K0
4
MCLR
3749 VPP
3
OSC2
2
POWERSAVE OSC1
STEREO TUNED CLKIN
GP<0:5>
F743
MUTE 6710 F744
BAV70
F743
F744
+5V
3798
22K
1765
SKR
14
12
13
11
{POWERSAVE,MUTE}
Figure 1-26 Microcontroller functions
Frequency setting
Frequency setting is necessary when the 4-position slide switch
is changed. In an internal look-up table the 4 required frequen-
cies 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.
The AV-version of RX Amplifier board
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
7100-D,7100-A
3144
sensitivity 1.4Vrms
1106
F135
1 R
F137
2
F138
L
3
F139
4
+10V
3117 3126
F140
5
7104
(active high)
F142
6 MUTE
MUTE
F144
7 POWERSAFE CONTROL
(active high)
sensitivity 2.5Vrms
7105,7108 7107
F120
1109
1
WIRED POWER
WIRED
F121
R
3 MUTE SAFE
AUDIO
F125
IN DRiVER CONTROL
2 L
(3,5MM
5
F122
stereo MUTE WIRED
jack)
F110
+29,5V "+Power"
7106
F128
+ Analog
1104 STANDBY
F129 DRIVER
1
+15V
2
From
SMPS
3
Conn. J2 +10V
F134
4
-15V
F141
F136
F143
- Analog
F119
1 2
-29,5V "-Power"
From SMPS Conn. J3
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.
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.
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" informa-
tion. 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
The main supply can be switched off with the "powersave"
control line to reduce the current consumption. The
MUTE
microcontroller is always powered by the power supply. All
other electronics can be put into powersave mode.
CL36532008_086.eps
290403
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.
+ Analog + Power
7101
TDA8920
5104,2122
Input Driver
F111
F112
Input Driver
F114
F117
7100-C,7100-B 5105,2125
Temperature
protection
6100
F127
Mode
OSC - Power
mute
6101
C5V1
MUTE_AMPn
- Analog
6103
6106
C2V7
7110 7109
"ON" "STANDBY"
LED LED
DRIVER DRIVER
F124 F123
6109 6110
GREEN RED
Standby out
F145
3
1107
update mdi 13-03-03
Figure 1-27 Block diagram amplifier
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.
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.
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.
MUTE_RX
STANDBY
MUTE_WIRED
1100
F113
4
8 Ohm/50W
3
F115 This signal is coming from zener 6101 via diode 6100.
2
8 Ohm/50W
Transistor 7104 and 7107 are not saturated at that moment.
1
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 condi-
tion).
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
11-25
+/- 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.
+10V
6100 F127
BAS316
3133
7104
BC847B
47K
BC847B
+10V
3141
22K
6105
3142 3143
7107
BC847B
BAS316 10K 47K
3146
7108
BC847B
10K
OPTION
Figure 1-28 Mute ampn circuit
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
+10V +10V
F123
F124
3150
7109
BC847B
100K
3151
7110
BC847B
47K
MUTE_AMPn
7112
3153
10K
+10V
3155
STBY_OUT
2K2
7106
BC847B
CL36532008_108.eps
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