Kenwood NX-740H Service Manual page 16

2.4.7 Power Supply Circuit
• When the power switch on the display unit is pressed, the power port on the display unit which is connected pin 140 (POWKEY),
goes low, then pin88 (SBC) goes high, Q718 turns on, SB SW (Q719) turns on and power (SB) is supplied to the transceiver.
• When the DC power supplied to the transceiver, the voltage regulator IC (IC720&IC718) and supply into the MCU VDD and reset
voltage detect IC (IC723). IC723 will generate signal (RESET) into the reset terminal on the MCU (IC714) to carry out a power on
reset.
• When the DC power voltage deceases from normal voltage, the INT voltage detector IC (IC722) will set to high on MCU port 141
(BATT_INT). If B line becomes less than about 8.5V, MCU will send the backup data to EEPROM (IC716) and go into STOP mode.
This circuit has an overvoltage protection circuit. If a DC voltage of 18V or higher is applied to the base of Q712, this voltage turns
Q712 on and sets port 141 (BATT_INT) to low. As a result port 88 (SBC) is low, and turns Q719 and Q720 (SB) off.
2.5 SEMICONDUCTOR DATA
2.5.1 MCU: 2F405ZGT6KFKA (TX-RX unit IC714)
Pin Port Name I/O
No.
1 LEDI O LED Data
2 LECE O LED Enable
3 LECL O LED Clock
4 LELH O LED Latch
5 LERE O LED Reset
6 VBAT - 3.3V
7 ACR_SW O ACR switch for HSDO(D/A) port
8 NC I No connection
9 NC I No connection
10 I2CDT I/O Function P8I/O Expander I2C Data
11 I2CCK I/O Function P7I/O Expander I2C Data
12 EVOL_DACCE O Function P6CE for EVOL
13 EVOL_SCLK O Function P5CLK for EVOL
14 EVOL_DATA O Function P4DATA for EVOL
15 /INT15P I/O Function P3I/O Expander Interrupt
16 VSS - GND
17 VDD - 33MD
18 BEEP O Beep for Side Tone
19 NC I No connection
1-16 (No.RA010<Rev.001>)
SB
Q706
IGN
SW
SBC
IC714
33MA
MCU
33MD
BATT
POWKEY
BATT_INT
POWER
SW
Fig.16 Power supply circuit
Function
Q719
SW
Q718
SW
IC720
AVR
IC718
IC721
AVR
AVR
Q712
SW
IC723
AVR
IC722
AVR
Pin Port Name
No.
20 PCBVER
21 IFDET
22 DISC_DC
(optional)
23 XIN
24 NC
25 RESET
26 LSDI
27 HSDI
28 TEMP_1
29 TEMP_2
30 VDD
31 VSSA
32 VREF+
33 VDDA
34 TEST_TX
35 TEST_RX
36 FNC_1(TXD0)
37 FNC_2(RXD0) I/O Function P2(RXD)
38 VSS
B
D715
I/O Function
I PCB version identification
I IFDET for ACR improvement
I for Discriminator DC Level
Adjustment
I Crystal (19.2MHz)
I No connection
I MCU Reset pin
I Low-Speed Data Input
I High-Speed Data Input
I Temperature 1
I Temperature 2
- 33MD
- GND
- 33MA
- 33MA
I/O UART_TX for Debug
I/O UART_RX for Debug
I/O Function P1(TXD)
- GND