Kenwood NX-840, Service Manual

Page: 16 / 54

1-16 (No.RA011<Rev.001>)
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.
Fig.16 Power supply circuit
2.5 SEMICONDUCTOR DATA
2.5.1 MCU: 2F405ZGT6KFKA (TX-RX unit IC714)
Q706
SW
Q719
SW
Q718
SW
IC721
AVR
D715
B
IC723
AVR
IC720
AVR
SBC
IGN
R898
R899
R969
R970
BATT_INT
33MD
33MA
BATT
IC714
MCU
POWER
SW
POWKEY
RESET
IC722
AVR
Q712
SW
SB
IGN
IC718
AVR
Pin
No. Port Name I/O Function
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
20 PCBVER I PCB version identification
21 IFDET I IFDET for ACR improvement
22 DISC_DC
(optional) I for Discriminator DC Level
Adjustment
23 XIN I Crystal (19.2MHz)
24 NC I No connection
25 RESET I MCU Reset pin
26 LSDI I Low-Speed Data Input
27 HSDI I High-Speed Data Input
28 TEMP_1 I Temperature 1
29 TEMP_2 I Temperature 2
30 VDD - 33MD
31 VSSA - GND
32 VREF+ - 33MA
33 VDDA - 33MA
34 TEST_TX I/O UART_TX for Debug
35 TEST_RX I/O UART_RX for Debug
36 FNC_1(TXD0) I/O Function P1(TXD)
37 FNC_2(RXD0) I/O Function P2(RXD)
38 VSS - GND
Pin
No. Port Name I/O Function