Icom IC-F70DS, Service Manual

4 - 5

BPF

From FM IF IC 
(IC3, pin 11)

To AF volume

From 
MIC amplifier
(IC203; FRONT UNIT)

To FM/PM SW 
(IC302, pin 5)

• DIGITAL MODE BLOCK DIAGRAM

DSP UNIT

AMP

AMP

Q303 

IC302 

RECEIVED SIGNAL 

FI1 

IC5 

IC8 

IC7

IC9 

IC9 

IC4 

IC302 

IC301 

A/D

LINER

CODEC

IC

LINER

CODEC

IC

BASE

BAND

IC

DIG/ANA

 SW

DSP

IC

MIC SW

LPF

TRANSMIT SIGNAL 

4-5 DIGITAL CIRCUIT (IC-F70DT/DS only)

• WHILE RECEIVING

A portion of the 2nd IF sigal from the limiter amplifier section 
in the FM IF IC (IC3) is output from pin 11 and is applied to 
the 2nd IF amplifier (Q303). The amplified 2nd IF signal is 
applied to the DSP UNIT via J2 (pin 11). 

The 2nd IF signal from the MAIN UNIT is passed through 
the ceramic BPF (DSP UNIT; FI1) to suppress heterodyne 
noise, and amplified again at the digital IF amplifier (DSP 
UNIT; IC5, pin 4). The amplified 2nd IF signal is applied to 
the A/D converter (DSP UNIT; IC8, pin 3) to be converted 
into digital IF data, then applied to the DSP IC (DSP UNIT; 
IC7). The DSP IC converts the digital IF into the digital audio 
signal.

The digital audio signal from the DSP IC are converted into 
analog audio signals at the LINER CODEC IC (IC9) and out-
put from pin 16. The audio signals from the LINER CODEC 
IC are applied to the MAIN UNIT via J1 (pin 22).

The audio signals from the DSP UNIT are applied to the 
base band IC (MAIN UNIT; IC301, pin 20) after being 
passed through the digital/analog switch (MAIN UNIT; IC302 ).

• WHILE TRANSMITTING

The microphone signals from the base band IC (IC301, pin 7) 
are applied to the DSP UNIT via J2 (pin 4).

The microphone signals from the MAIN UNIT are applied 
to the LINER CODEC IC (DSP UNIT; IC9, pin 2) to convert 
into the  digital audio signal.

The converted digital audio signal is processed by the DSP 
IC (DSP UNIT; IC7), and applied to the LINER CODEC IC 
(DSP UNIT; IC9) again. The signal from the LINER CODEC 
IC (IC9, pin 15) is passed through the LPFs (DSP UNIT; 
IC4, pins 3, 4, 5, 7) and applied to the MAIN UNIT via J1, 
and then passed through the microphone switch (MAIN 
UNIT; IC302, pins 3, 4), FM filter (R328, C335), FM/PM 
switch (IC302, pins 2, 15).

4-6 PORT ALLOCATIONS

4-6-1 CPU (IC307)

Pin 

number

Port 

name

Description

4–7

R1, R2,

R4, R8

Input ports for rotary selector (VR 
UNIT; S1).

10

SSO

Outputs serial data to the PLL IC (IC1, 
pin 15) and D/A converter (IC303, pin 8).

11

SCK

Outputs clock signal to the PLL IC (IC1 
pin 14) and D/A converter (IC303, pin 7), etc.

13

PLST

Outputs strobe signals to the PLL IC 
(IC1, pin 16).

15

DASW

Outputs control signal to the digital 
/analog switch (IC302).
 Low: 

While analog mode is selected.

16

TXC

Outputs the T5V switch (Q305) con-
trol signal.
 Low: 

During transmit.

17

TMUT

Outputs the ALC amplifi er (IC5) con-
trol signal.
 Low: 

During receive.

18

AFON

Outputs control signal for AF mute 
circuit (FRONT UNIT; IC205) and AF 
power amplifi er (FRONT UNIT; IC201).
 High: 

AF amplifi er (IC201) is activated.

19

NWC

Outputs wide/narrow switch (D13, 
D14) control signal. 
 High: 

When narrow mode is selected.

Pin 

number

Port 

name

Description

20

DDSD

Input port for serial data from the 
DTMF decoder IC (IC300, pin 9).

21

DDAC

Outputs clock signals to the DTMF 
decoder IC (IC300, pin 10).

26

R5C

Outputs R5V switch (Q306) control signal.
 High: 

While 

receiving.

27

S5C

Outputs S5V switch (Q304) control 
signal.
  High: In power save mode..

29

PTTO

Input port for optional unit.
 Low: 

Switch 

ON.

30

EM

Input port for the emegency switch 
(FRONT UNIT; S117).
 Low: 

While emegency switch is 
pushed.

32

RMUT

Input port for the AF mute signal from 
the optional unit via J1 or J2. 
 Low: 

While RX audio is muted.

33

MMUT

Input port for the microphone mute 
signal from the optional unit via J1 or 
J2. 
 Low: 

While microphone audio is 
muted.

34–36

OPT1–

OPT3

I/O ports for the connected optional 
unit to J1.