Kenwood TK-3148 Service Manual page 18

TK-3148
● FFSK
The FFSK input signal from the IF IC is amplified by IC300
(1/ 2) and goes to pin 5 of IC500. The signal is demodulated by
FFSK demodulator in IC500. The demodulated data goes to
the CPU for processing.
8. Power Supply Circuit
Battery +B is supplied via a 3A fuse from the battery terminal
connected to the TX-RX unit. After passing through the power
switch, power supply (SB) is applied to the three AVRs. IC5
supplies 5V (5M) to the control circuit, and IC9 supplies 5V
(5C) to common circuits. IC6 supplies to the TX circuit, the RX
circuit and common circuits of needless save mode. During
transmission, 5TC becomes Low and Q405 is turned ON to
supply 5V (5T) to the TX circuit. During reception, 5RC becomes
Low and Q404 is turned ON to supply 5V (5R) to the RX Circuit.
The power supply voltage monitor IC (IC404) monitors
power supply voltage (SB). If the voltage falls (less than 5V),
the VOUT port goes "LOW" level, the CPU INT port also goes
"LOW" level, and the CPU stops.
18
CIRCUIT DESCRIPTION /
IC500
AF IC
IC300
IC306
AMP
LPF
IC301
DTMF
DECODE
IC500
OSC1
XOUT
PD
Fig. 12 Decode / 图 12 解码
F400
+B
SB D405
ON/OFF
VOL
Fig. 13 Power supply circuit / 图 13 电源电路
电路说明
FFSK
●
来自于中频芯片的 FFSK 输入信号被 IC300（1/2）放大，然后
进入 IC500 的管脚 5。此信号被 IC500 中的 FFSK 解调器解调。已
解调的数据进入 CPU 执行操作。
IC303 IC201
BPF BPF
3
HSD
23
LSD
IN
IN
IC307
CPU
DCK,SD,STD
11
IC312
8．电源电路
经由来自于连接到 TX-RX 单元的电池端点的 3A 保险丝提供
电池＋ B。 通过电源开关后，电源 （SB）向 3 个 AVRs 提供电压。
IC5向控制电路提供5V （5M） 电压， IC9向共用电路提供5V （5C）
电压。IC6 向 TX 电路，RX 电路和共用电路的保存模式提供电
压。在发送过程中，5TC 变为低电平，且 Q405 接通并向 TX 电
路提供5V （5T） 电压。 在接收过程中， 5RC变为低电平， 且Q404
接通并向 RX 电路提供 5V（5R）电压。
电源电压监测 IC（IC404）监测电源电压（SB） 。如果电压下
降（低于 5V） ，则 VOUT 端口变为"低"电平，CPU INT 端口
也变为"低"电平，CPU 停止运行。
RF power amp (Q103 and Q106)
14
IC401 VCC
10
IC400 RESET
IC309
CPU
71
INT
IC404
IC403
5C
CE
Q405
IC402
5T
CE
5TC
Q404
5R
5RC
5CNS