Kenwood TK-373G Service Manual

UHF FM TRANSCEIVER

TK-373G

SERVICE MANUAL

© 2002-1 PRINTED IN JAPAN

B51-8618-00 (S) 931

Knob (ENCODER)
(K29-5331-03)

Knob (VOLUME)
(K29-5332-03)

Button knob (PTT)
(K29-5334-13)

Button knob
(MONI/LAMP)
(K29-5333-13)

CONTENTS

GENERAL ......................................................................2

SYSTEM SET-UP .......................................................... 2

OPERATING FEATURES..............................................3

REALIGNMENT ............................................................. 7

DISASSEMBLY FOR REPAIR..................................... 10

CIRCUIT DESCRIPTION .............................................11

SEMICONDUCTOR DATA ..........................................15

DESCRIPTION OF COMPONENTS............................ 16

PARTS LIST.................................................................18

EXPLODED VIEW .......................................................25

PACKING .....................................................................26

Cabinet assy
(A02-3568-33)

Key top (4 keys)
(K29-9142-02)

ADJUSTMENT .............................................................27

PC BOARD VIEWS

DISPLAY UNIT (X54-3250-11)............................... 37

TX-RX UNIT (X57-650X-XX)..................................39

SCHEMATIC DIAGRAM .............................................. 45

BLOCK DIAGRAM ....................................................... 49

LEVEL DIAGRAM ........................................................ 51

KNB-14/KNB-15A (Ni-Cd BATTERY) ..........................52

KNB-20N (Ni-MH BATTERY)....................................... 52

KMC-17/KMC-21 (SPEAKER MICROPHONE)............53

SPECIFICATIONS ................................... BACK COVER

TK-373G

GENERAL / SYSTEM SET-UP

INTRODUCTION

SCOPE OF THIS MANUAL

This manual is intended for use by experienced technicians
familiar with similar types of commercial grade
communications equipment. It contains all required service
information for the equipment and is current as of the
publication date. Changes which may occur after publication
are covered by either Service Bulletins or Manual Revisions.
These are issued as required.

ORDERING REPLACEMENT PARTS

When ordering replacement parts or equipment
information, the full part identification number should be
included. This applies to all parts, components, kits, or chassis.
If the part number is not known, include the chassis or kit
number of which it is a part, and a sufficient description of the
required component for proper identification.

Unit

Model &

destination

TK-373G

TX-RX Unit Display Unit Frequency range Remarks

K X57-6500-10 450~470MHz IF1 : 49.95MHz

K2 X57-6500-11

X54-3250-11

470~490MHz LOC : 50.4MHz

PERSONNEL SAFETY

The following precautions are recommended for personnel

safety:

●

DO NOT transmit until all RF connectors are verified secure
and any open connectors are properly terminated.

●

SHUT OFF and DO NOT operate this equipment near
electrical blasting caps or in an explosive atmosphere.

●

This equipment should be serviced by a qualified technician only.

SERVICE

This radio is designed for easy servicing. Refer to the
schematic diagrams, printed circuit board views, and alignment
procedures contained within.

SYSTEM SET-UP

Merchandise received

License and frequency allocated by FCC

Choose the type of transceiver

Transceiver programming

Are you using the optional antenna?

NO

Are you using the speaker microphone?

NO

Delivery

Frequency range (MHz) RF power Type

TX/RX 450~470
TX/RX 470~490

A personal computer (IBM PC or compatible), programming interface (KPG-22),
and programming software (KPG-76D) are required for programming.
(The frequency, TX power HI/LOW, and signalling data are programmed for the transceiver.)

YES

YES

KRA-15

Whip antenna

(Option)

KMC-17 or KMC-21

Speaker microphone

(Option)

4.0W

4.0W

TK-373G K

TK-373G K2

2

OPERATING FEATURES

TK-373G

1. Operating Features

Antenna

ww

qq

w

q

ww

qq

rr

r

rr

tt

t

tt
yy

y

yy
uu

u

uu

The transceiver is shown with the optional KNB-14 battery pack.

qq

q Rotary encoder

qq

Your dealer can program the encoder as either
System Up/Down or Group Up/Down. Rotate to
select a system or group.

ww

w Transmit/ Battery low indicator

ww

This red LED lights during transmission. If
programmed by your dealer, when the batter y pack
power is low, the LED flashes during transmission.
Replace or recharge the battery pack at such a time.

ee

e Power switch/ Volume control

ee

Turn clockwise to switch ON the transceiver. Rotate
to adjust the volume. To switch OFF the transceiver,
turn counterclockwise fully.

rr

r PTT (Push-to-Talk) switch

rr

Press this switch, then speak into the microphone to
call a station.

tt

t Side 1 key

tt

This is a PF (Programmable Function) key.

yy

y Side 2 key

yy

This is a PF (Programmable Function) key.

uu

u A, B,

uu

∞∞

55

∞,

5 keys

∞∞

55

These are PF (Programmable Function) keys.

ii

i Speaker /Microphone jacks

ii

Connect an optional speaker/ microphone here.

oo

o Display

oo

Note: The PF keys are programmed with default functions:

•

Side 1 key: Lamp

•

Side 2 key: Squelch Off Momentary

•

A key: None

•

B key: None

∞∞

•

∞

key: Group Down

∞∞

55

•

5

key: Group Up

55

ee

e

ee

Speaker

Microphone

ii

i

ii

oo

o

oo

Display

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Programmable Auxiliary Functions

You can program the Side 1, Side 2, A, B,
with the functions listed below.

•Aux

• Display Character

• DTMF ID (BOT)

• DTMF ID (EOT)

• Group Down

• Group Up

• Home Group

• Key Lock

• Lamp

• Memory (RCL)

• Memory (RCL/STO)

• Memory (STO)

• Monitor Momentary

• Monitor Toggle

• None (No function)

• Redial

• RF Power Low

• Scan

• Scan Del/Add

• Scan Temporary Delete

• Squelch Off Momentary

• Squelch Off Toggle

• System Down

• System Up

• Telephone Disconnect

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sademmargorpsipuorgdetceles

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metsys

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55

5 keys

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3

TK-373G

OPERATING FEATURES

2. Programmable keys

The functions the FPU programs to the function keys are

described in the following sections.

1) AUX

If this key is pressed, a dot appears at the extreme right of
the LCD and AUX port which is inside of the transceiver
turns to the active level. If pressed again, the dot disappears
and the AUX ports turns to the deactive level.

2) Display character

This key switches the LCD display between the system/
group number and system/group name.

3) DTMF ID (Begin of TX)

Pressing this key in Conventional mode, automatically sends
the preset DTMF ID (Begin of TX).

4) DTMF ID (End of TX)

Pressing this key in Conventional mode, automatically sends
the preset DTMF ID (End of TX).

5) Group up/down

When the key is pressed each time, the group number to
be selected is incremented/decremented and repeats if held
for one second or longer.

6) Home group

Each pressing of the key selects a preset system/group.

12) RF power low

Used to temporarily switch transmission output to low power.
Turning the function on enables:

Hi→Low, Low→Low
Key states are backed up, except in the PC mode when
they are reset.

13) Scan

Pressing this key starts scanning. Pressing this key again
stops scanning.

14) Scan Del/Add

Used to select whether system scan routines are used during
system scan. Each pressing of the key (to ON) toggles
between lockout and lock. The scan routine is started when
on lock. The DEL indicator flashes when the system is on
lockout.

15) Scan temporary delete

This key is temporarily deleted a system being scanned. If
you press this key when scan is stopped (when a call is
being received from another station), the system is
temporarily deleted and scanning restarts.
This key operates even when “Scan Type” is set to “List
Type System Scan”.

16) Squelch off

Used to release signalling or squelch when operating in
conventional mode.

7) Key lock

Pressing this key causes the transceiver to accept entry of
only the [Monitor Toggle], [Key Lock], [PTT], [Lamp], [Monitor
Momentary], [Squelch off Momentary], and [Squelch off
Toggle] keys.

8) Lamp

This key illuminates the LCD and keys on the front panel.
When the key is pressed, the LED lamp goes on.
When it is released, the lamp goes off after about five
seconds. If any key is pressed while the LED lamp is on,
the lamp is kept on for five seconds.

9) Memory

This key allows DTMF memory data to be recalled; up to 32
memories each with a memory dial of up to 16 digits
and an A/N of up to 8 digits per memory.

10) None

An error operation beep sounds, and no action will occur.
Use this function when the transceiver is required to be
operated more simply.

11) Redial

Pressing this key when System/Group is shown, displays
the previously transmitted DTMF code. Pressing [PTT] at
this time, transmits the code that is currently displayed.

4

17) System up/down

When the key is pressed each time, the system number to
be selected is incremented/decremented and repeats if held
for one second or longer.

18) Telephone disconnect

Pressing this key ends an RIC connection (disconnects the
telephone line).

3. Scan Operating

1) System scan

System scan can be selected with the “Scan” key by

programming the scan feature. When the “Scan” key is pressed
and the “SCN”’ mark appears, scan mode in entered. Scanning
starts from the system following the currently displayed system.
When a call is received, scanning stops, and the system and
group are displayed.

When the system knob or programming key is touched

during scanning, the scan stops and the revert system or group
can be changed. Scanning resumes one second after the key
is released.

System Scan consists of the following 2 types.

●

Fix system scan

All the set systems except locked-out ones are scanned. If

the DEL/ADD feature is assigned to the programmable key, it
can be controlled from the front panel.

OPERATING FEATURES

TK-373G

●

List type system scan

A scan list can be set for each system.
The list to be scanned can be changed by changing the

display system

If many system have been set, the scan speed can be
increased by narrowing the systems to be scanned with scan
lists.

2) System lockout

The system lockout feature is used to lock systems out of
the scan sequence, and can be selected by programming in
the following two ways:

●

Fixed lockout

The system to be locked out is selected by programming.
When a locked system is selected, the Delete (
appears on the left of the SYSTEM indicator. The revert system
is scanned even if it is locked out. If there is a locked system,
the Delete (

●

User selectable lockout

If the scan lockout feature is programmed to a key, the user
can lock systems out of the scan sequence with the key. To
lock a system out of the scan sequence, press the key when
the system is displayed. The Delete (
on the left of the SYSTEM indicator.

To unlock a system, select the system and press the key.
The Delete (
has returned to the scan sequence. The revert system is
scanned even if it is locked out. If there a locked system, the
Delete (
are locked out, the scan stops and only the revert system is
received.

) indicator flashes during fixed scanning.

) indicator is displayed

) indicator disappears to indicate that the system

) indicator flashes during fixed scanning. If all systems

) indicator

3) Drop-out delay time (Scan resume time)

If a call is received during scan, the scan stops. The scan
resume time can be programmed as 0 to 300 seconds in one­second increments. The default value is 3 seconds.

4) Dwell time

The dwell time is the time after transmission ends until the
scan resumes in scan mode. It can be set 0 to 300 seconds by
programming. The default value is 3 seconds.

5) System/Group revert

System/Group revert can be programmed for one of the
following;

the drop out delay time, the system/group is assigned as the
new revert system/group.

●

Selected revert

If the system/group was changed while scanning, the newly

selected system/group.

●

Selected + talkback

If the system/group was changed while scanning, the newly
selected system/group. The transceiver “talkback” on the
current receive group.

6) Scan message wait

The time for staying with the home repeater that receives a
signal during system scan and monitoring data messages can
be programmed. If there is no signal from the home repeater,
the system is scanned for about 50ms. If there is a signal,
three data messages are monitored. Normally, three data
messages are monitored for each system, and it can be
increased in multiples of three data messages per line to up to
eight lines.

If the repeater data message indicates that there is no call,
data monitoring is terminated and the home repeater of the
next system is scanned.

7) Group scan operation

Group scan can be programmed for each group. In addition
to the ID codes of the selected group, the ID codes of the
other groups that are permitted for group scan are decoded.
(The two fixed ID and block decode codes are always decoded.)

If, during group scanning, a call is received with one of the
selectable group ID codes for which group scan is enabled,
the group display indicates the group number that the call came
in with. That group then becomes the new selected group.
Group scan resumes after the specified dropout delay time or
dwell time shared by the system scan elapses.

8) In Conventional system.

If QT or DQT is set for the group, the groups, including
signalling, are scanned.

In case of the priority group is set in conventional system, if
a group scan (including group scan during a system scan)
temporarily stops (receiving) in a group that does not have
priority, a look back is performed to the priority group. Look
back is performed according to the look back time A and B
settings. If a call is received on the priority group, reception
immediately switches to the priority group.

●

Last called revert

The system/group changes to the revert system or group

when a call is received with the system/group being scanned.

●

Last used revert

If a system/group call is received during scanning and the

PTT button is pressed for transmission and response within

4. Details of Features

1) Time-out timer

The time-out timer can be programmed in 15 seconds
increments from 15 seconds to 600. If the transmitter is keyed
continuously for longer than the programmed time, the
transmitter is disabled and a warning tone sounds while the

5

TK-373G

OPERATING FEATURES

PTT button is held down. The alert tone stops when the PTT
button is released.

2) PTT ID

PTT ID provides a DTMF ANI to be sent with the PTT button
every time it is used (Begin of TX ID at beginning of
transmission, End of TX ID at end of transmission, or both).

You can program the PTT ID as one of the followings.

Off, BOT (Begin of TX ID), EOT (End of PTT ID), BOTH.

You can program PTT ID “on” or “off” for each group.

The transceiver is capable of having ID. The format is DTMF.

The timing that the transceiver sends the ID is
programmable.

Begin of TX ID (BOT) :Begin of TX ID is sent at the

beginning of transmission.

End of TX ID (EOT) : End of TX ID is sent at the end of

transmission.

Both : Begin of TX ID is sent at the beginning of transmission

and End of TX ID is sent at the end of transmission.

There is also a "PTT ID" setting for each group.

3) Battery Warning

This transceiver has a battery warning feature. If low voltage
is detected during transmission, the transceiver warns you by
a flashing red "LED".

When the voltage is detected to be even lower during
transmission, the transceiver stops transmission and warns
you by a flashing red "LED" and a beep.

Please notice "indication" for the battery exchange, charging
time by flashing red LED and beep.

4) Radio password

When the password is set in the transceiver, user can not
use the transceiver unless enter the correct password.

This code can be up to 6 digits from 0 to 9 and input with
the keypad or selector, and “A” key.

5) Call indicator

The call indicator can be programmed for each group. In
trunked system, it can be set to respond to a selectable decode
ID or one of two fixed IDs, except block IDs. When a call is
received with a selectable decode ID, the call indicator flashes.
When a call is received with a fixed ID, the call indicator lights
continuously.

On a conventional system, the call indicator can be
programmed to light for each QT or DQT code. It keeps flashing
while a call is being received. It is turned off by pressing any
front panel key.

6) Free system ringback

This feature is available only when a telephone
interconnected ID code is selected. If a busy tone sounds when
the PTT button is pressed, the transceiver enters this mode
automatically.

When the PTT button is released, a beep sounds for 400ms

to indicate that the mode has been entered. If the scan is on, it
is resumed (the “SCN” mark goes on). When any repeater
becomes available, a ringing tone sounds and this mode ends.

The mode is terminated when the system, group, scan, PTT,

key is changed.

7) System search

This feature can be programmed to automatically access
other programmed systems when the selected system cannot
be accessed. If an intercept tone sounds when the PTT button
is pressed after setting the mode, the transceiver has entered
the mode.

If the group ID is a telephone interconnect ID, the transceiver
then attempts to access, in succession, other systems that
have a telephone interconnect ID in the revert group location.
If the group ID is a dispatch ID, the transceiver attempts to
access other systems that have a dispatch ID programmed in
the revert group location.

If there is no system to be accessed, an intercept tone
sounds, the mode is terminated, and the transceiver returns to
the first system. If the access is successful, the mode is
terminated, and the searched system becomes the new
selected system (If during scanning, the scan stops).

8) Transpond

This feature can be programmed to turn on and off for each
group. If the ID of the group for which transpond is enabled is
received, two data messages (transmit ID and turn-off code)
are automatically transmitted if the PTT button is not pressed
as a response within the time set (0 to 300 seconds in 1-second
increments). If the PTT button is pressed within the time, the
transpond is not preformed.

9) Transmit inhibit

The transceiver can be programmed with a transmit inhibit
block of ID codes. If an ID code within this block is decoded
the preset time before the PTT button is pressed, transmission
is inhibited. The BUSY indicator lights and a busy tone sounds
until the PTT button is released to indicate that transmission is
not possible (except clear-to talk mode).

Transmission with the group for which the encode ID is not
set is inhibited, and the busy tone is output while the PTT button
is held down, regardless of the clear-to -talk setting.

5. Audible user feedback tones

The transceiver outputs various combinations of tones to
notify the user of the transceiver operating state. The main
tones are listed below

The high tone is 1477Hz, the mid tone is 941Hz, and the
low tone is 770Hz.

• Power on tone

This tone is output when the transceiver is turned on. (The
high tone is output for 500ms.)

6

TK-373G

OPERATING FEATURES

• Alert tone

This tone is output when the transceiver is in TX inhibition
for TOT, battery warning and PLL unlocked. It is output until
the PTT button is released. (The 697Hz tone is output.)

• Busy Tone

In trunked mode the busy tone informs the user when the
repeater cannot be used (System busy or TX inhibit Status).

• Intercept tone

This tone indicates that the transceiver is out of range. It
indicates that the PTT button is pressed, and transmission has
started, but the repeater cannot be connected and talking is
not possible. It is output until the PTT button is released. (The
mid tone and low tone are output alternately in 200ms intervals.)

• Delay tone

This tone is output when the PTT button is pressed and the
repeater is accessed three times or more to indicate connection
with the repeater is delayed. This tone is the same as the busy
tone. (It is not output of CLEAT TO TALK has been set to
YES.)

• Proceed tone

This tone is output when the PTT button is pressed,
transmission starts, and the repeater is connected to indicate
that the user can talk if the Clear-to-talk function has been set.
(The high tone is output for 100ms.)

/ REALIGNMENT

REALIGNMENT

1. Modes

User mode

Panel test mode

PC mode

Firmware
programming mode

Clone mode

Mode Function

User mode For normal use.
Panel test mode Used by the dealer to check the

Panel tuning mode Used by the dealer to tune the radio.
PC mode Used for communication between the

Data programming Used to read and write frequency data
mode
PC test mode Used to check the radio using the PC.

Firmware program- Used when changing the main
ming mode program of the flash memory.
Clone mode Used to transfer programming data

Panel tuning mode

Data programming
mode

PC test mode

Checksum

fundamental characteristics.

radio and PC (IBM compatible).

and other features to and from the radio.

This feature is included in the FPU.
See panel tuning.

from one radio to another.

PC tuning mode

• Free system ringback mode tone, system search mode

tone

This tone indicates that the transceiver is free system
ringback mode or system search mode. (The low tone is output
for 400ms.)

• Ringing tone

This tone indicates that the transceiver can use the repeater
in free system ringback mode. (The mid tone and no tone are
output eight cycles alternately in 50ms intervals.)

2. How to Enter Each Mode

Mode Operation

User mode Power ON
Panel test mode
PC mode Received commands from PC
Panel tuning mode [Panel test mode]+[A]
Firmware programming mode

Clone mode [Side1]+[5]+Power ON

[∞]+Power ON (Two seconds)

[Side1]+[Side2]+Power ON
(Two seconds)

(Two seconds)

3. For the panel Test Mode

For the setting method, refer to ADJUSTMENT.

3-1. For the panel Tuning Mode

For the setting method, refer to ADJUSTMENT.

7

TK-373G

REALIGNMENT

4. Checksum

Executing this function, “-PC-” appears on the display of

TK-373G while calculating the checksum .

When the calculation is completed, the display returns to

normal and PC displays the checksum of the radio.

5. PC Mode

5-1. Preface

The TK-373G transceiver is programmed using a personal
computer, a programming interface (KPG-22) and
programming software (KPG-76D).

The programming software can be used with an IBM PC or
compatible. Figure 1 shows the setup of an IBM PC for
programming.

5-2. Connection procedure

1. Connect the TK-373G to the personal computer with the

interface cable.

2. When the POWER is switched on, user mode can be

entered immediately. When the PC sends a command, the
radio enters PC mode.
When data is transmitted from transceiver, the red LED blink.
When data is received by the transceiver, the green LED blinks.

IBM-PC

Notes:

• The data stored in the personal computer must match model
type when it is written into the flash memory.

• Change the TK-373G to PC mode, then attach the interface
cable.

5-3. KPG-22 description

(PC programming interface cable: Option)

The KPG-22 is required to interface the TK-373G to the
computer. It has a circuit in its D-subconnector (25-pin) case
that converts the RS-232C logic level to the TTL level.

The KPG-22 connects the SP/MIC connector of the TK­373G to the computers RS-232C serial port.

5-4. Programming software description

The KPG-76D programming disk is supplied in 3-1/2” disk
format. The software on this disk allows a user to program the TK­373G radios via a programming interface cable (KPG-22).

5-5. Programming with IBM PC

If data is transferred to the transceiver from an IBM PC with
the KPG-76D, the destination data (basic radio information)
for each set can be modified. Normally, it is not necessary to
modify the destination data because their values are
determined automatically when the frequency range (frequency
type) is set.

The values should be modified only if necessary. Data can
be programmed into the flash memory in RS-232C format via
the universal connector.

RF Power meter
or SSG

KPG-76D

6. Firmware Programming Mode

6-1. Preface

Flash memory is mounted on the TK-373G. This allows the
TK-373G to be upgraded when new features are released in
the future. (For details on how to obtain the firmware, contact
Customer Service.)

6-2. Connection procedure

Connect the TK-373G to the personal computer (IBM PC
or compatible) with the interface cable (KPG-22). (Connection
is the same as in the PC Mode.)

6-3. Programming

1. Start up the programming software (FPRO.EXE).

2. Set the communications speed (normally, 57600 bps) and

communications port in the Setup item.

8

KPG-22

+

SP

}

­+

MIC

}

-

Tuning cable
(E30-3216-05)

Gray
Gray/Black

1.5D-XV Lead wire
Gray-XV Shield wire

Fig. 1

3. Set the firmware to be updated by file name item.

4. Hold down the [Side1] and [Side2] switches on the TK-373G,
and press the power switch.
When the [Side1] and [Side2] switches are held down for
two seconds, "PROG 576" appears on the display and
the LED lights orange. When "PROG 576" is displayed,
release the switches.

5. Check the connection between the TK-373G and the
personal computer, and make sure that the TK-373G is in
Program mode.

6. Click “write” button in the window. A window opens on the
display to indicate the writing progress. When the TK-373G
begins to receive data, the LED lights green.

7. When data is received successfully, a checksum appears
on the display.

REALIGNMENT

TK-373G

8. If you want to continue programming other TK-373Gs,
repeat steps 4 to 7.

Notes:

●

This mode cannot be entered if the Firmware Programming
mode is set to Disable in the Programming software (KPG­76D).

●

When programming the firmware, it is recommend to copy
the data from the floppy disk to your hard disk before you
update the radio firmware.
Directly copying from the floppy disk to the radio may not
work because the access speed is too slow.

6-4. Function

1. If you press the [Side2] switch while "PROG XXX" is
displayed, the checksum is displayed. If you press the
[Side2] switch again (while the checksum is displayed),
"PROG XXX" is redisplayed.

2. A transmission speed can be selected by pressing the [Side1]
switch while "PROG XXX" is displayed.
19200 bps: The LED flashes green and red alternately.

38400 bps: The LED flashes orange.
57600 bps: The LED lights orange.

Cloning cable parts No.

E30-3410-05 (TK-373G → TK-373G)

PTT/RXD

φ

3.5

GND
REMOTE/TXD

φ

2.5

Cloning cable

Fig. 2

φ

2.5

φ

3.5

Note:

Normally, write in the high-speed mode.

7. Clone Mode

Programming data can be transferred from one radio to
another by connecting them via their SP/MIC connectors. The
operation is as follows (the transmit radio is the master and
the receive radio is the slave).

1. Turn the master TK-373G power ON with the [Side1]+[5]

key held down. The TK-373G displays "

2. Power on the slave TK-373G.

3. Connect the cloning cable to the SP/MIC connectors on

the master and slave.

4. Press the [A] key on the master while the master displays

"

CLONE ". The data of the master is sent to the slave.
While the slave is receiving the data, "-PC-" is displayed. When
cloning of data is completed, the master displays "END", and
the slave automatically operates in the User mode. The slave
can then be operated by the same program as the master.

5. The other slave can be continuously cloned. When the [A]
key on the master is pressed while the master displays
"END", the master displays "

CLONE ". Carry out the

operation in steps 2 to 4.

Note: You can clone the programmed data between the

transceiver frequency version must be same.
Use the new clonig cable for TK-372G/373G.
You cannot use the old cloning cable for TK-360/370.

CLONE ".

9

TK-373G

DISASSEMBLY FOR REPAIR

Separating the case assembly from the chassis.

1. Remove the two knobs z and three round units x.

2. Remove the two screws

3. Expand the right and left sides of the bottom of the case
assembly, lift the chassis, and remove it from the case
assembly

c

v

v



.

c

c

.

x

z

x

z

x

Separating the chassis from the unit.

1. Remove the three screws ..
Lift the unit (X54), and rise up the connecter lever in the

arrow with your finger

Remove the three hexagonal bosses

twelve screws

2. Remove the solder from the antenna terminal using a

soldering iron, then lift the unit off (X57).

m

.

/

, and remove the

Ω

.

❾

X54-

❾

❾

❿

X57-

Antenna teminal

4. Taking cure not to cut the speaker lead b, open the chassis and
case assembly, and pull the speaker lead with connector

b

CN3

n

n

.

➐

X57-

➐

➐

➐

➐

➐

➐

➐

➐

➐

➐

➐

10

CIRCUIT DESCRIPTION

5R

Q14

Q17

D14

R78

R75

C263

C265

R80

D13

Q23

R98

R108

C133

CD1

R79

W/N

"H" : Wide
"L" : Narrow

MXO

IFI

MXI

IFO

AFO

IC4
FM IF SYSTEM

Q22

5R

W/N

C107

R74

C108

CF1

CF2

R81

QAD

R105

TK-373G

1. Frequency configuration

The receiver utilizes double conversion. The first IF is 49.95
MHz and the second IF is 450 kHz. The first local oscillator
signal is supplied form the PLL circuit.

The PLL circuit in the transmitter generates the necessary
frequencies. Fig. 1 shows the frequencies.

CF

SYSTEM

50.4MHz

multiply

450kHz

IF

X3

PLL

VCO

ANT

TX/RX : 450~470MHz (K)
TX/RX : 470~490MHz (K2)

RF

ANT

AMP

SW

PA

TX

AMP

AMP

MCF

49.95MHz

RX : 400.05~420.05MHz (K)
RX : 420.05~440.05MHz (K2)

TX/RX : 450~470MHz (K)
TX/RX : 470~490MHz (K2)

Fig. 1 Frequency configuration

2. Receiver

The frequency configuration of the receiver is shown in Fig. 2.

ANT

RF
AMP
Q301

BPF

ANT

SW

CF1 : Wide

CF2 : Narrow

IC4

IF, MIX, DET

X3 multiply

IC14

HPF LPF HPF BEF

5

2nd Local

Q12

21

Fig. 2 Receiver section

BPF

AF AMP

IC16 (2/2)

TCXO

MIXER

Q19

1st Local

DE-

EMP

MCF
XF1

PLL

VCO

AF AMP

IC15(2/2)

EXP

IF AMP

Q22

AF VOL

MUTE

AF

AMP

TCXO

MIC

AMP

41

16.8MHz

AF AMP

IC11

SP

MIC

3) IF Amplifier circuit

The first IF signal is passed through a four-pole monolithic
crystal filter (XF1) to remove the adjacent channel signal.
The filtered first IF signal is amplified by the first IF amplifier
(Q22) and then applied to the lF system IC (IC4). The IF
system IC provides a second mixer, second local oscillator,
limiting amplifier, quadrature detector and RSSI (Received
Signal Strength Indicator). The second mixer mixes the first
IF signal with the 50.4MHz of the second local oscillator
output (TCXO X3) and produces the second IF signal of
450kHz.
The second IF signal is passed through the ceramic filter
(CF1; Wide, CF2 ; Narrow) to remove the adjacent channel
signal. The filtered second IF signal is amplified by the
limiting amplifier and demodulated by the quadrature
detector with the ceramic discriminator (CD1). The
demodulated signal is routed to the audio circuit.

4) Wide/Narrow changeover circuit

Narrow and Wide settings can be made for each channel
by switching the ceramic filters CF1 (Wide) and CF2
(Narrow).
The WIDE (high level) and NARROW (low level) data is
output from IC5 (OUTPUT EXPANDER), pin 4.
When a WIDE (high level) data is received, Q14 turn off
and Q17 turn on. When a NARROW (low level) data is
received, Q14 turn on and Q17 turn off. D14 and D13 are
switched to ceramic filters when a high/low level data is
received.
Q23 turns on/off with the Wide/Narrow data and the IC4

SP

detector output level is changed to maintain a constant
output level during wide or narrow signals.

1) Front end (RF AMP)

The signal coming form the antenna passes through the
transmit/receive switching diode circuit, (D3,D7) passes
through a BPF, and is amplified by the RF amplifier (Q301).
The resulting signal passes through a BPF and goes to the
mixer.

2) First mixer

The signal from the front end is mixed with the first local
oscillator signal generated in the PLL circuit by Q19 to
produce a first IF frequency of 49.95 MHz.
The resulting signal passes through the XF1 MCF to cut
the adjacent spurious and provide the optimum
characteristics, such as adjacent frequency selectivity.

Fig. 3 Wide/Narrow changeover circuit

11

TK-373G

CIRCUIT DESCRIPTION

5) Audio amplifier circuit

The demodulated signal from IC4 is amplified by IC16 (2/2),
high-pass filtered, low-pass filtered, high-pass filtered, band­eliminate filtered, and de-emphasized by IC14.
The signal then goes through an AF amplifier IC15 (2/2), an
AF volume control (VR2), and is routed to an audio power
amplifier (IC11) where it is amplified and output to the speaker.

6) Squelch

Part of the AF signal from the IC enters the FM IC (IC4)
again, and the noise component is amplified and rectified
by a filter and an amplifier to produce a DC voltage
corresponding to the noise level.
The DC signal from the FM IC goes to the analog port of
the microprocessor (IC13). IC13 determines whether to
output sounds from the speaker by checking whether the
input voltage is higher or lower than the preset value.
To output sounds from the speaker, IC6 sends a high signal
to the SP MUTE line and turns IC11 on through
Q32,Q33,Q34 and Q30. (See Fig. 4)

7) Receive signaling

QT/DQT/LTR
300Hz and higher audio frequencies of the output signal from
IF IC are cut by a low-pass filter (IC19). The resulting signal
enters the microprocessor (IC13). IC13 determines whether
the QT, DQT or LTR matches the preset value, and controls
the SP MUTE and the speaker output sounds according to
the squelch results.

IF AMP

FM IF IC4

DET

IC16 (2/2)

IF AMP

21

IC14

HPF LPF HPF BEF

5

DE-

EMP

43

EXP

IC15 (2/2)

AF AMP

MUTE

AF PA AMP

IC11

from the phase comparator in IC2. The output signal from
the phase comparator is filtered through a low-pass filter
and passed to the VCO to control the oscillator
frequency.(See Fig. 5)

2) VCO

The operating frequency is generated by Q2 in transmit
mode and Q10 in receive mode. The oscillator frequency is
controlled by applying the VCO control voltage, obtained
from the phase comparator, to the varactor diodes (D2 and
D4 in transmit mode and D9 and D11 in receive mode).
The T/R pin is set high in receive mode causing Q7 and Q8
to turn Q2 off and turn Q10 on.
The T/R pin is set low in transmit mode. The outputs from
Q10 and Q2 are amplified by Q3 and sent to the buffer
amplifiers.

D2, 4

LPF

D9, 11

PLL IC IC2

1/N

41

Q30

SP

SW

PLL DATA

REF OSC

1/M

Q2

TX VCO

Q10

RX VCO

10kHz/12.5kHz

PHASE

COMPARATOR

10kHz/12.5kHz

Q3

BUFF AMP

Q7, 8

T/R SW

Q37,38

CHARGE

PUMP

Q1

X2 multiply

Q4

RF AMP

IC19

LPF

93ANSQL

IC13

CPU

95

TOI

QT/DQT/LTR

Q36
SW

Fig. 4 AF Amplifier and Squelch

3. PLL frequency synthesizer

The PLL circuit generates the first local oscillator signal for

reception and the RF signal for transmission.

1) PLL

The VCO output is doubled by Q1 and then sent to the PLL
IC (IC2).
The frequency step of the PLL circuit is 10 or 12.5kHz.
A 16.8MHz reference an oscillator signal is divided at IC2
by a fixed counter to produce oscillator (VCO) output signal
which is buffer amplified by Q3 then divided in IC2 by a
dual-module programmable counter. The divided signal is
compared in phase with the 10 or 12.5kHz reference signal

12

Q32, 33, 34
SW

IC6

5

5RC

OUTPUT EXPANDER

SP

7

MUTE

16.8MHz

Fig. 5 PLL circuit

3) Unlock Detector

If a pulse signal appears at the LD pin of IC2, an unlock
condition occurs, and the DC voltage obtained form D1,
R1, and C6 causes the voltage applied to the microprocessor
to go low. When the microprocessor detects this condition,
the transmitter is disabled, ignoring the push-to-talk switch
input signal.(See Fig. 6)

5C

IC2

LD

PLL IC

R1

D1

C6

IC13

UL

MPU

Fig. 6 Unlock detector circuit

CIRCUIT DESCRIPTION

TK-373G

4. Transmitter System

1) Microphone amplifier

The signal from the microphone passes through the limiter
circuit in D23, and through the high-pass filter, the ALC
circuit, the low-pass filter, the high-pass filter, and pre­emphasis/IDC circuit IC14. When encoding DTMF, the mute
switch (Q35) is turned OFF for muting the microphone input
signal.
The signal passes through the D/A converter (IC17) for the
maximum deviation adjustment, and goes to the VCXO
modulation input.

MIC

D23

LIMIT

IC14

12

HPF

IC17

15

ALC

D/A

Fig. 7 Microphone amplifier

2) Drive and Final amplifier

The signal from the T/R switch (D5 is on) is amplified by the
pre-drive (Q5) and drive amplifier (Q6) to 50mW.
The output of the drive amplifier is amplified by the RF power
amplifier (IC1) to 4.0W (1W when the power is low). The
RF power amplifier consists of two MOS FET stages. The
output of the RF power amplifier is then passed through the
harmonic filter (LPF) and antenna switch (D3 is on) and
applied to the antenna terminal.

From

T/R SW

(D5)

Pre-DRIVE

+B

APC

(IC13)

Q5

AMP

R56
R57
R58

Q6 IC1

DRIVE

AMP

Fig. 8 Drive and final amplifier and APC circuit

3) APC circuit

The APC circuit always monitors the current flowing through
the RF power amplifier (IC1) and keeps a constant current.
The voltage drop at R56, R57 and R58 is caused by the
current flowing through the RF power amplifier and this
voltage is applied to the differential amplifier IC3(1/2).
IC3(2/2) compares the output voltage of IC3(1/2) with the

IC3

(1/2)

16

MUTE

Q35

SW

18 19

COMP

LPF HPF IDC

VCO

LPF

QT/DQT/LTR

TOVCO
22

IC13
CPU

RF

POWER AMP

VDD

IC3

(2/2)

98

TOTCXO

20

VGG

PRE

EMP

LPF

2

D3

ANT

SW

DTMF

(RX Audio)

DTMF

TCXO

reference voltage from IC13, and the output of IC3(2/2)
controls the VGG of the RF power amplifier to make both
voltages the same.
The change of power high/low is carried out by the change
of the reference voltage.

4) Encode signaling

(1) QT/DQT/LTR
QT,DQT,LTR data of the TOTCXO Line is output form pin
20 of the CPU. The signal passes through a low-pass CR
filter and goes to the TCXO(X1).
The QT,DQT,LTR data of the TOVCO Line is output form
pin 22 of the CPU. The signal passes through a low pass
CR filter, mixes with the audio signal, and goes to the VCO

6

modulation input. TX deviation is adjusted by the CPU. (See
fig.7)

(2) DTMF

X1

High-speed data is output from pin 2 of the CPU. The signal
passes through a low-pass CR filter, and provides a TX
and SP out tone, and is then applied to the audio processor

LPF

AF

AMP
IC15

(2/2)

(IC14). The signal is mixed with the audio signal and goes
to the VCO.
TX deviation is adjusted by the CPU. (See fig.7)

5. Power supply

There are five 5V power supplies for the microprocessor:
5V,5M,5C,5R, and 5T. 5V for microprocessor is always
output while the power is on. 5M is always output, but turns
off when the power is turned off to prevent malfunction of
the microprocessor.
5C is a common 5V.
5R is 5V for reception and output during reception.
5T is 5V for transmission and output during transmission.

6. Control Circuit

ANT

LPF

The control circuit consists of a microprocessor (IC13) and
its peripheral circuits. It controls the TX-RX unit and transfers
data to and from the display unit. IC13 mainly performs the
following:

(1) Switching between transmission and reception by the

PTT signal input.

(2) Reading system, group, frequency, and program data

from the memory circuit.
(3) Sending frequency program data to the PLL.
(4) Controlling squelch on/off by the DC voltage from the

squelch circuit.
(5) Controlling the audio mute circuit by the decode data

input.
(6) Transmitting tone and encode data.

13

TK-373G

IC13

IC12

CPU

IC10

EEPROM

FLASH

CIRCUIT DESCRIPTION

1) Frequency shift circuit

The microprocessor (IC13) operates at a clock of

9.8304MHz. This oscillator has a circuit that shifts the
frequency by BEAT SHIFT SW (Q31).

2) Memory circuit

Memory circuit consists of the CPU (IC13) and a flash
memory (IC12). A flash memory has a capacity of 2M bits
that contains the transceiver control program for the CPU
and data such as transceiver channels and operating
features.
This program can be easily written from an external device.
Data, such as DTMF memories and the operating status,
are programmed into the EEPROM (IC10).

●

Flash Memory

Note : The flash memory holds data such as written with the

FPU (KPG-76D) and firmware program (User mode, Test
mode, Tuning mode, etc.). This data must be rewritten when
replacing the flash memory.

●

EEPROM

Note : The EEPROM stores tuning data (Deviation, Squelch,

etc.).
Realign the transceiver after replacing the EEPROM.

Fig. 9 Memory circuit

3) Low battery warning

The battery voltage is monitored by the microprocessor
(IC13). When the battery voltage falls below the voltage set
by the Low Battery Warning adjustment, the LED flashes
red to notify the operator that it is time to replace the battery.
If the battery voltage falls even more (approx. 5.8V), a beep
sounds and transmission is stopped.

Low battery warning

The red LED flashes during
transmission.

The red LED flashes and a
continuous beep sounds
while PTT is pressed.

Battery condition

The battery voltage is low but
the transceiver is still usable.

The battery voltage is low and
the transceiver is not able to
make calls.

8. CONTROL SYSTEM

Keys and channel selector circuit.
The signal from keys and channel selector input to

microprocessor directly as shown in fig. 10.

Channel selector

5M

3

PTT

KOUT3

KOUT1

KOUT2

KEYAD

KOUT0

CN1

KIN4

IC13
CPU

KIN3

KIN2

KIN1

KIN0

25

EN1

16

EN2

27

EN3

CN501

87

AB

PTT
SW

47k

47k

100k

LAMP

SW

MONI

SW

Fig. 10 Control system

14