Kenwood TK-2140, Руководство по обслуживанию

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TK-2140
7
CIRCUIT DESCRIPTION
Center Frequency Nominal 455kHz
Band Width
6dB Min.
±
4.5kHz
40dB Max.
±
10.0kHz
Stop Band Attenuation
±
100kHz Min. 25.0dB
Ripple Within 455
±
3.0kHz Max. 1.5dB
Insertion Loss at 455 kHz Max. 6.0dB
Table 2 Ceramic filter (L72-0996-05): CF201
signal is routed to the audio circuit.
3-3. Wide/Narrow changeover circuit
Narrow and Wide settings can be made for each channel
by switching the ceramic filters CF200 (Wide), CF201 (Narrow).
The WIDE (high level) and NARROW (low level) data is
output from IC311.
Regardless of NARROW or WIDE band selection, signals
always pass through the filter, CF200.
When the WIDE band is selected, Q201 is turned ON, then
D202 and D203 are turned OFF.
So, the signal does not pass through the filter CF201. When
the NARROW band is selected, Q201 is turned OFF, then D202
and D203 are turned ON. So, the signal passes through the
filters, CF200 and CF201.
Q503 turns on/off with the Wide/Narrow data and the IC200
detector output level is changed to maintain a constant output
level during wide or narrow signals.
Q201
IC200
Q503
AFOUT
5R
R213 R210
CF201
CF200
D202 D203
R208 R216
R211
C206
C210
MIXOUT
AFOUT
QUAD IFOUT
IFIN
C221
R255
R221
CD200
R264
R256
W/N
5CNS
R222
Fig. 3 Wide/Narrow changeover circuit
3-4. Audio amplifier circuit
The demodulated signal from IC200 goes through the mute
switch (Q204) and is amplified by IC300 (2/2), high-pass filtered,
low-pass filtered, high-pass filtered, band-eliminate filtered, and
de-emphasized by IC500.
The signal then goes through an AF amplifier IC305 (2/2),
an electronic volume control (IC307), and an AF switch (Q308
is on), and is routed to audio power amplifier (IC313), where it
is amplified and output to the internal speaker.
The audio mute signal (AM1) from the shift register becomes
Low in the standby and Q302, Q303 which are power supply
circuit for IC313 turn off. Also, IC500 is set to the power down
mode according to data from microprocessor, and the AF signal
is muted. When the audio is output, AM1 becomes High to
turn Q302, Q303 ON, and voltage is supplied to power terminal
VP of IC313. Also, IC500 is canceled out of the power down
mode.
The speaker is switched by the logic of speaker switching
terminal SSW on the universal connector. When SP-MIC is
not attached, the logic of SSW becomes High and SW (Q308)
is turned ON, and the AF signal is input to both amplifiers of
IC313.
When SP-MIC is attached, SSW is connected to GND at
inside of SP-MIC. For this reason, Q308 is turned OFF, and
the AF signal is input only to amplifier for EXT SP of IC313.
Change of INT/EXT SP refer to Fig. 4.
AM1 SSW VC1 VC2 SP
H H H L INT
H L L H EXT
L H L L MUTE
L L L L MUTE
Fig. 4 Audio amplifier circuit
SW
IC313
2
8
AM1
AF
SSW
INT.SP
EXT.SP
Q303
Q302
SB
VP 5
VC1
VC2
Q307
Q305