Philips Streamium MX6000i, Руководство по обслуживанию

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10-2 10-2
Block diagram and Operation
• Clock oscillator
The clock frequency is generated around IC7600. Using 2 extra transistors (7602 and 7608) and 2 ceramic resonators it can
be operated at 2 frequencies: 602.7kHz and 700kHz. The frequency is selected by the signal “FREQ_HOP” coming from
connector 1302 pin 9.
When FREQ_HOP is low, the output of 7600-1 will be high. This switches transistor 7602 on, and connects resonator 1600
(602.7kHz) to inverter 7600-3. Similarly, when FREQ_HOP is high, resonator 1601 is connected to 7600-3.
The output frequency is divided by two by IC7607, resulting in 301.35kHz or 350kHz.
The purpose of a selectable clock frequency is related to the disturbance of the tuner which is built-in together with this
amplifier. In MW, the software of the set microprocessor will select the other clock frequency in case the amplifier clock
interfers with the tuned station.
• Class-D amplifier TDA8920 and low-pass filter
The TDA8920 is a two channel audio power amplifier using class-D technology. The audio input signal is converted into a
digital Pulse Width Modulated (PWM) signal via an analog input stage and PWM modulator. It is then fed to the power stage
which outputs a high power PWM signal which switches between the main supply lines.
The TDA8920 is followed by a 2nd-order low-pass filter. It has a cut-off frequency around 50kHz and converts the PWM signal
into analog audio signal across the loudspeaker.
The TDA8920 has a temperature protection and a current limiter built-in. Furthermore, via the mode input, the IC can be put in
active-, mute- and standby mode.
- Active mode (amplifier fully operational) with output signal.
- Mute mode; the amplifiers are operational, but the audio signal is muted.
- Standby mode; with a very low supply current, the output stage is switched off.
• DC-detection
The DC-detection circuit monitors all 6 outputs for DC. Whenever one or more outputs contain DC for more than 1 second, the
circuit will be activated. A positive voltage will activate transistor 7710 and pin 10 of connector 1302 will be pulled down. In
case of a negative voltage, transistor 7716 will be activated, which in turn activates 7710. The set microprocessor will take
further action.
Exploded View
MECHANICAL PARTS LIST & SCREWS
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8
4822 492 11735 SPRING, TRANSISTOR
9 – D2.3 x 8
Note: Only the parts mentioned in this list are normal service spare parts.
3104 217 07180 bl110
clock
generator
output 1
output 2
output 3
output 4
output 5
output 6
input 1
input 2
input 3
input 4
input 5
input 6
freq_hop
301.35 / 350 kHz
DC
detection
err
temp
NTC
TDA8920
TDA8920
TDA8920
output 1
input 1
TDA8920
SINGLE ENDED 6 x 75W BRIDGE 3 x 100W
+
-
input 2
TDA8920
+
-
input 3
TDA8920
+
-
clock
generator
freq_hop
301.35 / 350 kHz
DC
detection
err
temp
NTC
output 2
output 3