Panasonic Z8 / Chassis Service Manual / Other ▷ View online
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11.
AF Output Stage
The Z8 chassis uses two audio output ICs. TDA7253
is a mono audio amplifier and TDA7263 is the stereo
version. Both versions include internal muting, short
circuit protection and thermal overload protection.
is a mono audio amplifier and TDA7263 is the stereo
version. Both versions include internal muting, short
circuit protection and thermal overload protection.
11.1. Audio Output Devices
11.1.1. TDA7253
TDA7253 is a single output audio amplifier used on
mono models only. The amplitude controlled AF
signal is output from the audio out terminal pin 44 of
the UOC IC IC601. The AF signal is fed to the audio
output stage via C263 and R256. This capacitor may
be charged up very quickly as all control processes
together
mono models only. The amplitude controlled AF
signal is output from the audio out terminal pin 44 of
the UOC IC IC601. The AF signal is fed to the audio
output stage via C263 and R256. This capacitor may
be charged up very quickly as all control processes
together
with the baseband switch over are
processed in the UOC IC.
The AF signal is then input via pin 5 of the audio
output IC IC251. From here it is amplified and output
via pin 8. The AF signal is then fed via the headphone
terminal JK3101 to the internal speaker via connector
E7.
output IC IC251. From here it is amplified and output
via pin 8. The AF signal is then fed via the headphone
terminal JK3101 to the internal speaker via connector
E7.
11.1.2. TDA7263
TDA7263 is a dual output audio amplifier used on
stereo models only. Both amplitude controlled AF
signals are output from pins 24(R) and 25(L) of the
MSP IC2001. The signals are fed to the base of
transistors Q2001 and Q2002. The transistors are
used for impedance matching in order that the
interference on the audio lines between the MSP
IC2001 and the audio output IC IC251 is kept at a
minimum.
stereo models only. Both amplitude controlled AF
signals are output from pins 24(R) and 25(L) of the
MSP IC2001. The signals are fed to the base of
transistors Q2001 and Q2002. The transistors are
used for impedance matching in order that the
interference on the audio lines between the MSP
IC2001 and the audio output IC IC251 is kept at a
minimum.
The left audio signal is fed via transistor Q2002,
R2001, C266 and R261 before being applied to the
audio output IC IC251 pin 1. The right audio signal is
fed via transistor Q2001, R2002, C263 and R256
before being applied to the audio output IC IC251 pin
5. These capacitors may be charged up very quickly
as all control processes (volume, balance) together
with the baseband switch over are processed in the
MSP IC2001.
R2001, C266 and R261 before being applied to the
audio output IC IC251 pin 1. The right audio signal is
fed via transistor Q2001, R2002, C263 and R256
before being applied to the audio output IC IC251 pin
5. These capacitors may be charged up very quickly
as all control processes (volume, balance) together
with the baseband switch over are processed in the
MSP IC2001.
The AF signals input via pins 1 (L) and pin 5 (R) of the
audio output IC IC251,.are then amplified and output
via pins 8 (Rout) and 10 (Lout). Both AF signals are
audio output IC IC251,.are then amplified and output
via pins 8 (Rout) and 10 (Lout). Both AF signals are
fed via the headphone terminal JK3101 to the internal
speakers via connectors E6 and E7.
speakers via connectors E6 and E7.
11.2. Mute Functions
11.2.1. POP Mute
At pin 3 of IC251, a muting transistor Q255 is used to
prevent the internal amplifiers producing POP at
switch Off times. This is achieved by muting the
internal audio amplifiers during these periods.
prevent the internal amplifiers producing POP at
switch Off times. This is achieved by muting the
internal audio amplifiers during these periods.
The POP mute control is input at pin 3 of the audio
output IC IC251. Transistor Q255 provides the
switching of the mute function via R241. The control
signal that causes switching of Q255 is provided by
the POP mute control transistor Q253, which is used
to prevent POP during switch Off times. The base of
Q253 is held high via resistor R262 which is fed from
the standby rectifier output D1201.
output IC IC251. Transistor Q255 provides the
switching of the mute function via R241. The control
signal that causes switching of Q255 is provided by
the POP mute control transistor Q253, which is used
to prevent POP during switch Off times. The base of
Q253 is held high via resistor R262 which is fed from
the standby rectifier output D1201.
At switch On, Q253 is non-conducting since the base
and emitter are near the same potential. Capacitor
C257 begins to charge towards the +8V supply at the
anode terminal of diode D260.
and emitter are near the same potential. Capacitor
C257 begins to charge towards the +8V supply at the
anode terminal of diode D260.
At
switch Off,
transistor
Q253
base voltage
decreases, causing Q253 to switch On. This is due to
the charge held by capacitor C257, which is
prevented from discharging into the decreasing
supply line by diode D260. C257 now begins to
discharge via the collector / emitter junction of Q253.
The increased voltage present at the potential divider
R264 and R268 causes transistor Q255 to switch On.
This in turn, causes pin 3 of IC251 to be pulled Low,
resulting in the audio signals of IC251 being muted.
the charge held by capacitor C257, which is
prevented from discharging into the decreasing
supply line by diode D260. C257 now begins to
discharge via the collector / emitter junction of Q253.
The increased voltage present at the potential divider
R264 and R268 causes transistor Q255 to switch On.
This in turn, causes pin 3 of IC251 to be pulled Low,
resulting in the audio signals of IC251 being muted.
11.2.2. Active Mute
The active mute control is input at pin 3 of the audio
output IC IC251. Transistor Q255 provides the
switching of the mute function via R241. The control
path is fed from the mute terminal of the UOC IC
IC601 pin 11, which is pulled Low during normal
operation, is biased by resistor R1141 to the 5V
standby supply. During channel change, tuning and
muting operations, the Low level output from pin 11 is
disabled. This causes the voltage at the base of
transistor Q255 to increase, switching Q255 On. This
results in pin 3 of IC251 being pulled Low, resulting in
the audio output being muted.
output IC IC251. Transistor Q255 provides the
switching of the mute function via R241. The control
path is fed from the mute terminal of the UOC IC
IC601 pin 11, which is pulled Low during normal
operation, is biased by resistor R1141 to the 5V
standby supply. During channel change, tuning and
muting operations, the Low level output from pin 11 is
disabled. This causes the voltage at the base of
transistor Q255 to increase, switching Q255 On. This
results in pin 3 of IC251 being pulled Low, resulting in
the audio output being muted.
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12.
Appendices
12.1. SECAM AM Demodulator
French SECAM mono models require an additional
switching IC to process mono SIF signals. IC201
TDA9830 is a TV sound AM demodulator and audio
source switch.
switching IC to process mono SIF signals. IC201
TDA9830 is a TV sound AM demodulator and audio
source switch.
The SIF signal used for AM mono operation is fed
from the tuner via the IF processing stage (discussed
in section 4.4.2.) and fed via the IF inputs at pins 1 and
16 of the AM demodulator / audio switch IC201.
from the tuner via the IF processing stage (discussed
in section 4.4.2.) and fed via the IF inputs at pins 1 and
16 of the AM demodulator / audio switch IC201.
IC201 performs demodulation by passing the signal
through
through
its
internal
processing
stages.
The
demodulated signal is output at the AM out terminal
at pin 6 of IC201, and is fed back into pin 7 of IC201
at pin 6 of IC201, and is fed back into pin 7 of IC201
via decoupling capacitor C214, where the switch is
held permanently On by pin 9 being inactive.
Capacitor C214 is used to prevent any effects of
switching on the input stage.
held permanently On by pin 9 being inactive.
Capacitor C214 is used to prevent any effects of
switching on the input stage.
The audio switch is an operational amplifier whose
output is determined by the mute control at pin 12 of
IC201. This is controlled by the presence of either
positive
output is determined by the mute control at pin 12 of
IC201. This is controlled by the presence of either
positive
(SECAM)
or
negative
(PAL/NTSC)
modulation, the trigger voltage being provided by the
NEG/POS control terminal fed from pin 7 of the UOC
IC IC601.
The audio signal path from the switch, output at pin
8 of IC201, is discussed in section 4.4.2.
NEG/POS control terminal fed from pin 7 of the UOC
IC IC601.
The audio signal path from the switch, output at pin
8 of IC201, is discussed in section 4.4.2.
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12.2. Monitor Output
The Z8 chassis may be used as a monitor for use in
specialised applications such as surveillance. The Z8
monitor differs from the TV such that it does not
require an RF transmission signal via the tuner since
all video inputs and outputs are routed via the AV
sockets. Therefore, the tuner and IF input stages are
omitted in the Z8 monitor.
specialised applications such as surveillance. The Z8
monitor differs from the TV such that it does not
require an RF transmission signal via the tuner since
all video inputs and outputs are routed via the AV
sockets. Therefore, the tuner and IF input stages are
omitted in the Z8 monitor.
The Monitor Output circuit is used to provide
impedance matching to and from external video input
sources via the AV sockets. This allows several
monitors to be connected in cascade.
impedance matching to and from external video input
sources via the AV sockets. This allows several
monitors to be connected in cascade.
The video signal is input via RCA video (located at the
front of the monitor) or pin 20 of the AV 21 pin scart.
From here the video signal input level and impedance
front of the monitor) or pin 20 of the AV 21 pin scart.
From here the video signal input level and impedance
are matched by the terminator resistor R3115 to
provide a 1V video input level. This video input is split
into two paths.
provide a 1V video input level. This video input is split
into two paths.
The first path sees the video signal being input via pin
42 of the UOC IC IC601 where processing is
performed as discussed in section 4.6.
42 of the UOC IC IC601 where processing is
performed as discussed in section 4.6.
The second path is fed via capacitor C3106 and
resistor R3113 to amplifier transistor Q3105. The
signal is then fed via resistor R3135 to matching
transistor Q3106. This provides the matching
necessary to output to an external video source.
From here the signal is fed to the video output path via
buffer transistor Q3104 as discussed in section 4.6.
The video signal is output via pin 19 of the 21 pin scart
socket (JK3102).
resistor R3113 to amplifier transistor Q3105. The
signal is then fed via resistor R3135 to matching
transistor Q3106. This provides the matching
necessary to output to an external video source.
From here the signal is fed to the video output path via
buffer transistor Q3104 as discussed in section 4.6.
The video signal is output via pin 19 of the 21 pin scart
socket (JK3102).
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Notes
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