Kenwood TK-3230 Service Manual page 9

Control System
■ Reset Circuit
When a battery voltage is dropped, IC401 is detected
low voltage, and this detected signal input to IC403 for stop
the MCU function. IC400 is detected the reset voltage.
■ Battery Voltage Detection Circuit
The unit detects a low battery voltage and display the
BATT indicator on the LCD. The battery voltage is divided
and applied to the analog value input pin (BATT) of the MCU,
and converted to a digital signal.
■ Power Supply Circuit
The power supply voltage is maintained to 3.0V by the
series regulator (IC404). It is used as MCU power 3M, 3C,
3R and 3T.
The B (battery voltage) is supplied to the RF final
transistor Q104.
T h e t r a n s m i s s i o n p o w e r 3 T i s s u p p l i e d t o t h e
transmission output circuit when the MCU turns Q404 on
only in transmit mode.
The reception power 3R is provided to the receive and IF
circuits when the MCU turns Q406 on only in receive mode.
The transmission/reception power 3C is supplied to
the VCO and PLL circuits when the MCU turns Q405 on in
transmit and receive modes.
If no signal is received for 10 seconds, the MCU enters
the power save mode, and turns common power 3C and
reception power 3R on for one cycle and off for three cycles
according to the signals from the MCU to save the battery
power.
CIRCUIT DESCRIPTION
■ QT/DQT
• Encode (Transmit)
signal (IC403 pin 18 (TO)) goes to TCXO modulation and
VCO modulation (Through the VR300).
• Decode (Receive)
of IC301 is LPF for sub-audible frequency. This signal goes
to IC403 pin 77 (TI). IC403 is detected the QT or DQT.
QT/DQT signal is generated by MCU (IC403). Output
Detected AF signal go to IC300 and then IC301. Function
B
Power
SW
IC404
AVR
BATT
IC403
MCU
Fig. 9 Reset, Battery voltage detection and
Power supply circuits
18
TO LPF
IC403
MCU
IC301
77
TI LPF
Fig. 10 QT/DQT circuit
TK-3230
SB
3M
Q405
SW 3C
Q406
SW 3R
Q404
SW 3T
TCXO
VR300
VCO
TX AF
IC300 IC200
Baseband
IF IC
IC
9