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KT-990D
CIRCUIT DESCRIPTION
Function of components
Tuner unit (XO05-3420-1 1)
Use/Function
Operation/Condition/Interchangeability
FM IF amplifier
Miner
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FM OSC (TUNED) buffer
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OSC buffer
Q10
AM power switch
Power switch for AM circuitry.
FM/AM
power control
When the base is 'H"' (set by 5V from the microprocessor), Q10
is turned ON setting the AM mode.
Qi2=14
| PLL Woop Titer
ae ric a
RNG EC
Q15,16
DIS/DIR switching
Goes ON when the input is "H". Turns Q17 and Q18 ON.
Q17,18
DIS/DIR switching
Driver. Q17 is ON for DIS and Q78
is ON for DIR.
Q19~21
WIDE/NARROW
switching
When the input to Q19
is "H", Q20 is turned ON (Wide).
Q22
STOP control
When the output from IC8 (2/2) is "L'', Q22 is turned ON and
the STOP signal goes "L".
Q23
STOP SENSE switching
SENSE is High when the input is "H".
Q24,25
REC CAL control
REC CAL is set when the input to Q24 is "H".
Components
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Q4,5
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Q26
AM switching
Switches the AM signal.
Q27
REC CAL switching
Switches REC CAL.
Q28
Forced Mono control
Forced Mono mode is set when the input is
"'H
Q34
Auto quieting control
Automatically controls the SUB demodulation level during the
small antenna input operation.
Q35
38kHz sine wave generator amplifier | Using the tuning circuit (88kHz) of LC as the load, turns the
rectangular wave into a sine wave.
Sends the 38kHz
signal from the tank circuit to the SUB
demodulator at a low impedance.
Used as the load resistance to IC18
Performs current regulating operation together with Q37.
Used as the load resistance to IC 18.
Performs current regulating operation together with Q39.
Constant-current load (GND side).
Goes ON in Narrow mode to control the separation (Narrow).
Q36
38kHz buffer amplifier
Current
mirror
constant-current
circuit
Q43
Q44
SUB signal demodulation switching | OFF in Stereo mode, ON is Mono mode
Q51,52
OUTPUT muting
Used for muting the output signal.
053,54
Muting control
Muting is activated when the base of Q54 is "'L".
Gain switching
Q58.59
Regulator
For +28V Tr.
}asos"
Regulator
For +5V PLL, prescaler IC
Regulator
—17.5V for FL.
O55
Regulator
Main 15V output.
Q56,57
Regulator
—13V output
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