Kenwood 144MHz FM TRANSCEIVER K2E Service Manual page 11

Voltage Detection Circuit
Various voltages are input to the A/D port of the MPU (IC8)
for processing.
Battery voltage is divided with resistors (R240, R241) and
enters the BATT terminal (pin 52) of the MPU.
Battery voltage is used for battery meter indication during
transmission or for alert tone processing when an abnormal
power supply voltage (approx. 16.5 V or higher) is applied.
Squelch voltage becomes DC voltage by detecting changes
in noise voltage in the FM IC (IC3), and the signal is used for
squelch control.
The S meter voltage is output from the RSSI pin of the FM
IC to control S meter display.
Detection of thermistor voltage (temperature) in the Ni-MH
battery during charging, detection of remote microphone key
pressing and VOX voltage monitoring are performed through
each A/D port of the MPU.
Battery Save Circuit
If there is no signal (squelch off, scan off or no key operation)
for longer than 10 seconds, the transceiver will enter the
battery save mode.
Battery save operation is performed by controlling Q57 with
an output signal from the 5C (SAVE) terminal (pin 15) of the
MPU.
The 5C ON/OFF cycle ratio during battery saving can be set
from a transceiver menu.
5MS
Q41
37
5MS
5C (SAVE)
15
IC8
MPU
Fig. 12 Battery save circuit
CIRCUIT DESCRIPTION
5C
5M
Q57
TH-K2AT/K2E/K2ET
LED Drive Circuit
The LCD and key illumination LEDs are lighted by controlling
Q51 for the LCD and Q50 for keys according to the output
voltage from the AF/LAMP AVR (Q37).
The BUSY and TX illumination LEDs are lighted by controlling
Q47.
D33 Q37
B
Q38
D48
AF AMP
D49
D41
BUSY LED
5C
D40
TX LED
Fig. 13 LED drive circuit
Q51
D42 D42 D42 D44 D46
D43 D43 D43 D47
Q50
56
LAMP
IC8
MPU
99
RX LED
Q47
R227
R226
5T
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