Kenwood TH-D72A Service Manual page 11

8. Control System
8-1. RESET, BACKUP circuit
When the supplied +B voltage falls, and the 33M voltage
is detected to be lower than the threshold voltage of the
RESET IC (IC726), the connected Main MCU (IC737) detects
this with the interrupt terminal (/RST), backs up the data to
the EEPROM ICs (IC730,IC731), and turns off the power.
8-2. LCD, LED, KEY circuit
The LCD Display is controlled by the driver built into the
Main MCU (IC737). The contrast is adjusted by the regulator
IC (IC701), similarly controlled by the LCDCNT signal from
the Main MCU (IC737).
On the other hand, the LEDs (D710~715, D718~724) for
the LCD and 16 KEY backlight are lit by the LAMP B power
supply through the DC switches (Q721, Q722). The port of
the Main MCU (IC737) corresponding to the 16 KEY is com-
posed of a 5x5 matrix and detects a pressed KEY by scan-
ning in the software.
LAMP B
Q722
PC
port
J702
COM
port
CIRCUIT DESCRIPTION
Q721 Backlight
LED
DC
SW
DC Regulator
SW
IC
IC703
J703
IC736
Vbus
SW
USB
driver
IC710
Q704
DC
33C
SW
IC709
TXD
IC702
SW IC
RS232C
RXD
driver
SW IC
IC708
Figure 7 Control circuit
TH-D72A/D72E
8-3. INT-GPS control
The GPS unit installed in the equipment communicates
directly with the Main MCU (IC737) and is controlled. The in-
ternal GPS power supply changes with the DC switch (Q701)
controlled by the Main MCU (IC737).
8-4. RTC function
The RTC IC (IC717) that operates with the lithium battery
has a clock function.
8-5. PC port
It corresponds to the connection to the external instru-
ment (PC) through the USB connector.
8-6. COM port
To correspond to the connection with the external GPS
equipment, it communicates by switching ICs (IC708,
IC709) by the Main MCU (IC737) / TNC MCU (IC727) and
the RS232C driver IC (IC702).
LCD
LCD
V cont
IC701
LAMP
Vbus_USB
IC737
Main
232B_S
MCU
VGPS
TXD_COM
GP_PS
SKY_SW
GP_ON
TXD_IGPS
RXD_COM RXD_IGPS
IC727
TXD_EGPS
TNC
RXD_EGPS
MCU
IC726
/RST
RESET
33M
IC
IC730,IC731
EEPROM
IC717 X701
RTC IC
33C
DC
Q701
SW
INT_GPS
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