Kenwood UBZ-LJ8 Service Manual page 6

UBZ-LJ8
■ Power Supply Circuit
The battery voltage directly supplies RF final amplifier (Q8)
and AF amplifier (IC203) through AVR (Q216).
IC207 supplies 3V voltage to MPU, EEPROM and power
key.
Switch Q211 delivers 3V supply 3MS to base band IC,
MIC amplifier and VOX circuit when necessary.
Switch Q215 delivers 3V supply 3C to VCO and PLL circuit
during receiving, transmitting or standby.
Switch Q212 delivers 3V supply 3R to FM IC, Mixer, RX
amplifier and IF amplifier during receiving or standby.
Switch Q210 delivers 3V supply 3T to TX amplifier Q14,
Q7, TX/RX switch and the power control circuit of Q8.
■ CTCSS Circuit
The tone frequency is generated by MPU (pin 57). This
PWM signal becomes a sinusoidal waveform after passing
through a RC low pass network. It will mix with voice signal
from base band IC and becomes modulation signal for VCO.
During receiving, the QT signal received from FM IC will
go through the base band IC so that signal with less than
6
CIRCUIT DESCRIPTION
Internal MIC
PTT
3MS
IC208
MIC
MPU
3
REM
R295
SP/MIC DET
AFO
Fig. 13 Speaker, microphone jack and Remote control circuit
D11
1
BUSY
2
RSSI
57
CTCSS OUT
64
CTCSS IN
Batt
Q216
IC208
MPU
AF IN SP
10
SP AMP
Q220
Fig. 14 CTCSS circuit
If there is no incoming signal or key press after 5 second,
unit will enter its power save mode. In power save mode, 3C
and 3R will be turned on and off respectively for power sav-
ing.
■ Remote Control Circuit
The voltage at the MPU REM (pin 3) will be converted into
a digital signal to carry out remote operation according to the
predetermined voltages level.
The REM pin is set to about 3V by pull up resistor. When
remote control switch is pressed, the voltage divided by the
resistor in series with the pull up resistor will generate a volt-
age for MPU to recognize the operation.
(SMC-34 remote control speaker microphone)
ø3.5
ø2.5
300Hz will be output via IC209 pin 21. Next, it will pass
through the low pass filter (IC211) so as to eliminate un-
wanted noise. Then the filtered tone will be passed to the pin
64 of MPU where the digital filter inside the MPU will detect
the tone. If the tone is matched, MPU will turn on the
speaker.
3R
7
FILOUT
Q13 IC2
FM IC
12
RSSI
AFOUT
1 5 21
IC209
IC211
Base
LPF
band IC
IC203
AF AMP
RC LPF
R273 R272
External MIC
External SP
Mixer RX AMP
9
23
7
TX AMP
VCO