Kenwood TH-K2AT Service Manual page 11

Voltage Detection Circuit
Various voltages are input to the A/D port of the M PU (IC8)
for processing.
Battery voltage is divided w ith resistors (R240, R241) and
enters the BATT terminal (pin 52) of the M PU.
Battery voltage is used for battery meter indication during
transmission or for alert tone processing w hen an abnormal
pow er 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-M H
battery during charging, detection of remote microphone key
pressing and VOX voltage monitoring are performed through
each A/D port of the M PU.
Battery Save Circuit
If there is no signal (squelch off, scan off or no key operation)
for longer than 10 seconds, the transceiver w ill enter the
battery save mode.
Battery save operation is performed by controlling Q57 w ith
an output signal from the 5C (SAVE) terminal (pin 15) of the
M PU.
The 5C ON/OFF cycle ratio during battery saving can be set
from a transceiver menu.
5M S
Q41
37
5M S
5C (SAVE)
15
IC8
M PU
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/LAM P AVR (Q37).
The BUSY and TX illumination LEDs are lighted by controlling
Q47.
D33 Q37
B
Q38
D48
AF AM P
D49
D41
BUSY LED
5C
D40
TX LED
Fig. 13 LED drive circuit
Q51
D46
D42 D42 D42 D44
D43 D43 D43 D47
Q50
56
LAM P
IC8
M PU
99
RX LED
Q47
R227
R226
5T
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