Panasonic EURO 4 Chassis Technical Manual page 83

25.3. Power ON/OFF Mute
During switch ON/OFF times the audio signals are
muted to prevent POP. This muting is achieved at
switch ON by the muting circuit located on the
C-Board, At switch OFF the mute circuit located on
the E-Board is used.
The muting signal fed from the Power ON muting
circuit on the C-Board is used to mute all the audio
outputs on the C-Board and K-board. The need for
this additional switch ON muting circuit is due to the
fact that the dolby power supply powers up quicker
than the main power supply. This results in the
amplifier ICs on the C-Board being powered up
before the main power supply has become
established, which results in POP.
The mute circuit on the C-Board consists of
transistor Q2706. At switch ON the 12V line which is
fed to the base of Q2706
taken for the main power supply to become
established. However the dolby power supply feds a
+18V supply to the emitter of
transistor to conduct, this HIGH level is then fed via
D2719 to the muting transistors Q2703,
Q2705 which are connected to the audio input pin
pin 1 of the audio amplifier ICs.
This mute line is also fed via connector C2 via pin 6
and onto the K-Board K5 pin 6. Here the mute signal
is fed to the following muting transistors:
:
Q2429 located on the K-Board which is used to
control the muting of transistors
with super 3D bass), Q2424, Q2422. These muting
transistors thus mute the audio being fed to the C, S
and Super 3D Bass before being fed to the C-Board.
Q2429 also controls the switch ON mute of the
headphone amplifier and transistors Q2430, Q2431.
is at a LOW due to time
Q2706 causing the
Q2704 and
Q2427 (only models
:
Q2416 is also fed the switch ON mute signal,
which is then used to mute the L, R, C, and S signals
being fed to the phono outputs, this muting being
carried out by Q2417, Q2418, Q2419,
Q2421.
During switch OFF operations to control the muting
transistors and prevent POP, the main switch
ON/OFF mute circuit made up of
the E-Board is used. This mute control being fed via
connector E11 pin 1 to connector K2 pin1.
The operation of this mute circuit being described in
section 10.1.
25.4. Amplifier IC (TDA2030AV)
The TDA2030AV is a class AB amplifier using low
cost complementary
provides high output current and very low harmonic
and cross over distortion.
The device also incorporates a short circuit circuit
protection system which automatically limits the
dissipated power which is used to keep the working
point of the transistors with in their safe operating
range, a thermal shut-down system is also included.
The Centre, Surround and Super 3D Bass which are
fed to the C-Board are input via connector C2, where
these audio signals are then fed to pin 1 of their
respective IC TDA2030AV, for which there are three.
These three ICs being IC2702,
Here the audio signals are amplified and output via
pin 4 and fed to the external speaker terminal
JK2702.
Negative feedback is fed from the output pin 4 via
the feedback loop back to pin 2, this being used to
control the amplification factor.
The TDA2030AV which works on a split supply sees
-18V being input via pin 3 and +18V being input via
pin 5.
83
3DQDVRQLF
Q2420
Q2101 located on
pairs. The TDA2030AV
IC2703 and IC2704.
and