Kenwood NX-420 K User manual

SERVICE MANUAL
This product complies with the RoHS directive for the European market. This product uses Lead Free solder.
© 2013-2 PRINTED IN JAPAN
B53-7050-00 (Y)561
NX-420
800MHz DIGITAL TRANSCEIVER
Knob (Volume)
(K29-9485-13)
Knob (Selector)
(K29-9486-13)
Knob (PTT)
(K29-9500-03)
Button knob
(Side1/Side2/AUX)
(K29-9501-03)
Plastic cabinet assy
(A02-4132-13)
Packing (16Key)
(G53-1865-11)
Plastic cabinet assy
(A02-4130-13)
Whip antenna
(T90-1114-05)
Knob (Volume)
(K29-9485-13)
Knob (Selector)
(K29-9486-13)
Knob (PTT)
(K29-9500-03)
Button knob
(Side1/Side2/AUX)
(K29-9501-03)
Whip antenna
(T90-1114-05)
NX-420 K NX-420 K3

NX-420
2
GENERAL....................................................3
SYSTEM SET-UP.........................................4
REALIGNMENT...........................................5
DISASSEMBLY FOR REPAIR.....................8
CIRCUIT DESCRIPTION ...........................12
COMPONENTS DESCRIPTION................18
PARTS LIST...............................................20
EXPLODEDVIEW......................................28
PACKING ...................................................29
TROUBLE SHOOTING..............................30
ADJUSTMENT...........................................33
TERMINAL FUNCTION .............................54
PC BOARD
DISPLAY UNIT (X54-3760-XX) ..............56
TX-RX UNIT (X57-8370-10)....................60
LEVEL DIAGRAM .....................................64
INTERCONNECTION DIAGRAM...............65
SCHEMATIC DIAGRAM ............................66
BLOCK DIAGRAM ....................................76
SPECIFICATIONS......................................79
CONTENTS
Document Copyrights
Copyright 2013 by JVC KENWOOD Corporation. All rights
reserved.
No part of this manual may be reproduced, translated,
distributed, or transmitted in any form or by any means,
electronic, mechanical, photocopying, recording, or other-
wise, for any purpose without the prior written permission of
JVC KENWOOD Corporation.
Disclaimer
While every precaution has been taken in the preparation
of this manual, JVC KENWOOD Corporation assumes no
responsibility for errors or omissions. Neither is any liability
assumed for damages resulting from the use of the informa-
tion contained herein. JVC KENWOOD Corporation reserves
the right to make changes to any products herein at any time
for improvement purposes.
Firmware Copyrights
The title to and ownership of copyrights for firmware
embedded in KENWOOD product memories are reserved
for JVC KENWOOD Corporation. Any modifying, reverse
engineering, copy, reproducing or disclosing on an Internet
website of the firmware is strictly prohibited without prior
written consent of JVC KENWOOD Corporation. Further-
more, any reselling, assigning or transferring of the firmware
is also strictly prohibited without embedding the firmware in
KENWOOD product memories.
Transceivers containing AMBE+2™ Vocoder:
The AMBE+2™ voice coding technology is embedded in
the firmware under the license of Digital Voice Systems, Inc.

NX-420
3
Model & Destination
(Market code)
Display unit X54-376X-XX
TX-RX unit
X57-8370-10 Frequency
range Remarks LCD+16key
0-10 0-12
NX-420
K- TX:806~825MHz
RX/TX:851~870MHz 1st IF: 49.95MHz LOC: 50.4MHz
–
K3 -
INTRODUCTION
SCOPE OFTHIS MANUAL
This manual is intended for use by experienced techni-
cians familiar with similar types of commercial grade com-
munications equipment. It contains all required service infor-
mation for the equipment and is current as of the publication
date. Changes which may occur after publication are cov-
ered by either Service Bulletins or Manual Revisions. These
are issued as required.
ORDERING REPLACEMENT PARTS
When ordering replacement parts or equipment informa-
tion, 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 re-
quired component for proper identification.
PERSONAL SAFETY
The following precautions are recommended for personal
safety:
• DO NOT transmit until all RF connectors are verified se-
cure 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 techni-
cian only.
SERVICE
This transceiver is designed for easy servicing. Refer to
the schematic diagrams, printed circuit board views, and
alignment procedures contained within.
GENERAL

NX-420
4
SYSTEM SET-UP
Merchandise received
Choose the type of transceiver
Transceiver programming
Are you using the speaker microphone?
A personal computer, programming interface (KPG-22A/22U) are
required for programming.
(The frequency, and signaling data are programmed for the transceiver.)
Frequency range (MHz) RF power LCD 16-key
No
Yes
No
Yes
Type
TX 806~825MHz 3W
3W
NX-420 K
NX-420 K3
NO (Option)
YES KMC-21/KMC-45
Speaker microphone
or
KMC-48GPS
GPS speaker microphone
Delivery
TX/RX 851~870MHz
TX 806~825MHz
TX/RX 851~870MHz

NX-420
5
1. Modes
User mode
Panel test mode *1
Firmware version information *1
Panel tuning mode *1
Data programming mode
PC test mode PC tuning mode
PC mode
Clone mode *1
Firmware
programming mode
Mode Function
User mode For normal use.
Panel test mode 1Used by the dealer to check the funda-
mental characteristics.
Panel tuning mode 1 Used by the dealer to tune the transceiver.
PC mode Used for communication between the
transceiver and PC.
Data programming
mode Used to read and write frequency data and other features to and from the transceiver.
PC test mode
Used to check the transceiver using the PC.
This feature is included in the FPU.
Firmware program-
ming mode Used when changing the main program of the flash memory.
Clone mode 1Used to transfer programming data from
one transceiver to another.
Firmware version
information 1Used to confirm the internal firmware ver-
sion.
1: K3 model only
2. How to Enter Each Mode
Mode Operation
User mode Power ON
Panel test mode 2[] + Power ON
PC mode Received commands from PC
Panel tuning mode 2 [Panel test mode] + [ ]
Firmware programming mode [Side1] + Power ON
Clone mode 2[] + Power ON
Firmware version information 2[] + Power ON
2: K3 model only
3. PanelTest Mode
(K3 model only)
Setting method refer to ADJUSTMENT.
4. PanelTuning Mode
(K3 model only)
Setting method refer to ADJUSTMENT.
5. PC Mode
5-1. Preface
The transceiver is programmed by using a personal com-
puter, programming interface (KPG-22A/22U) and program-
ming software (KPG-141D).
The programming software can be used with a PC. Fig-
ure 1 shows the setup of a PC for programming.
PC KPG-22A or KPG-22U
FPU
Tuning cable
(E30-3216-05)
D-SUB
(9-pin)
KPG-22A
PC
Gray
Gray/Black
1.5D-XV Lead wire
1.5D-XV Shield wire
+
–
+
–
SP
MIC
Transceiver Transceiver
USB
KPG-22U
PC
Fig. 1
5-2. Connection procedure
1. Connect the transceiver to the computer using the inter-
face cable.
Note:
• You must install the KPG-22U driver in the computer to
use the USB programming interface cable (KPG-22U).
REALIGNMENT

NX-420
6
2. When the POWER is switched on, you can immediately
enter user mode. When the PC sends a command, the
transceiver enters PC mode, and “PROGRAM” is dis-
played on the LCD.
When data is transmitting from the transceiver, the red
LED lights.
When data is receiving by the transceiver, the green LED
lights.
Note:
The data stored in the computer must match the “Model
Name” when it is written into the flash memory.
5-3. KPG-22A description
(PC programming interface cable: Option)
The KPG-22A is required to interface the transceiver to
the computer. It has a circuit in its D-sub connector case that
converts the RS-232C logic level to the TTL level.
The KPG-22A connects the SP/MIC connector of the
transceiver to the RS-232C serial port of the computer.
5-4. KPG-22U description
(USB programming interface cable: Option)
The KPG-22U is a cable which connects to a USB port on
a computer.
When using the KPG-22U, install the supplied CD-ROM
(with driver software) in the computer. The KPG-22U driver
runs under Windows XP, Vista or 7.
The latest version of the USB driver is available for down-
load from the following URL:
http://www.kenwood.com/usb-com/
(This URL may change without notice.)
5-5. Programming softwares KPG-141D (ver.3.10
or later) description
The KPG-141D is the programming software for the trans-
ceiver supplied on a CD-ROM. This software runs under
Windows XP, Vista or 7 on a PC.
The data can be input to or read from the transceiver and
edited on the screen.The programmed or edited data can be
printed out. It is also possible to tune the transceiver.
6. Firmware Programming Mode
6-1. Preface
Flash memory is mounted on the transceiver. This allows
the transceiver to be upgraded when new features are re-
leased in the future. (For details on how to obtain the firm-
ware, contact Customer Service.)
6-2. Connection procedure
Connect the transceiver to the personal computer using
the interface cable (KPG-22A/22U) and USB adapter (KCT-
53U: when the interface cable is KPG-22A, the KCT-53U can
be used.). (Connection is the same as in the PC Mode.)
6-3. Programming
1. Start up the firmware programming software (Fpro.exe
(ver. 6.10 or later)). The Fpro.exe exists in the KPG-141D
installed holder.
2. Set the communications speed (normally, 115200 bps)
and communications port in the configuration item.
3. Set the firmware to be updated by File name item.
4. Press and hold the [Side1] key while turning the transceiv-
er power ON. Then, the orange LED on the transceiver
lights and “FIRM PRG” is displayed.
5. Check the connection between the transceiver and the
personal computer, and make sure that the transceiver is
in the Program mode.
6. Press “write” button in the window. When the transceiver
starts to receive data, the [LOADING] display lights.
7. If writing ends successfully, the checksum is calculated
and a result is displayed.
8. If you want to continue programming other transceivers,
repeat steps 4 to 7.
6-4. Function
If you press the [Side1] key while “FIRM PRG” is dis-
played, the checksum is calculated, and a result is displayed.
If you press the [Side1] key again while the checksum is dis-
played, “FIRM PRG” is redisplayed.
Note:
• This mode cannot be entered if the Firmware Program-
ming mode is set to Disable in the Programming software.
• Normally, write in the high-speed mode.
• The text message are displayed for K3 model only.
7. Clone Mode (K3 model only)
Programming data can be transferred from one transceiv-
er to another by connecting them via their external SP/MIC
connectors. The operation is as follows (the transmit trans-
ceiver is the source and the receive transceiver is a target).
The following data cannot be cloned.
• Tuning data
• Embedded message with password
• Model name data
• ESN (Electronic Serial Number) data
Note:
The following data can be cloned.
• Fleet (own)/ID (own) for FleetSync
• Unit ID (own) for NXDN
• ID (own) for MDC-1200
1. Press and hold the [ ] key while turning the transceiver
power ON. If the Read authorization password is set to
the transceiver, the transceiver displays “CLN LOCK”. If
the password is not set, the transceiver displays “CLONE”.
REALIGNMENT

NX-420
7
2. When you enter the correct password, and “CLONE” is
displayed, the transceiver can be used as the cloning
source. The following describes how to enter the pass-
word.
3.
• How to enter the password using the keypad (K3
model only);
If one of keys 0 to 9is pressed while the “CLN LOCK” is
displayed, the pressed number is displayed on the LCD.
Each press of the key shifts the display in order to the left.
When you enter the password and press the [ ] or [ ] key,
“CLONE” is displayed if the entered password is correct. If
the password is incorrect, “CLN LOCK” is redisplayed.
• How to enter the password using the Selector (K3
model only);
If the Selector is rotated while “CLN LOCK” is displayed,
the Read authorization password input screen is dis-
played.
If the Selector is rotated while the Read authorization
password input screen is displayed, the number (0 to 9)
blinks on the LCD. When you press the [ ] key, the cur-
rently selected number is determined. If you press the [ ]
key after entering the password in this procedure, “CLONE”
is displayed if the entered password is correct. If the pass-
word is incorrect, “CLN LOCK” is redisplayed.
4. Power ON the target transceiver.
5. Connect the cloning cable (part No. E30-3410-05) to the
SP/MIC connectors on the source and target.
6. Press the [ ] key on the source while the source displays
“CLONE”. The data of the source is sent to the target.
While the target is receiving the data, “PROGRAM” is
displayed. When cloning of data is completed, the source
displays “END”, and the target automatically operates in
the User mode. The target can then be operated by the
same program as the source.
7. The other target can be continuously cloned. When the
[] key on the source is pressed while the source displays
“END”, the source displays “CLONE”.Carry out the opera-
tion in step 4 to 6.
Note:
• Cannot be cloned if the password (overwrite password) is
programmed to the target.
• “Model Name” must be same to clone the transceiver.
Cloning cable
(E30-3410-05)
Fig. 2
8. FirmwareVersion Information
(K3 model only)
Press and hold the [ ] key while turning the transceiver
power ON and then keep pressing and holding the [ ] key,
the firmware version information appears on the LCD.
REALIGNMENT

NX-420
8
DISASSEMBLY FOR REPAIR
1. Precautions for Disassembly
■Removing the selector knob and volume knob
1. Using a thin tool, insert it in the hole on the selector knob
side and push the knob spring. a
Note: When you push the knob spring, take care not to
damage the resin of the knob.
2. Lift and remove the selector knob bwhile pushing the
knob spring.
3. Repeat steps 1 and 2 for the volume knob, to remove the
volume knob c.
:
@
.
Note:
Perform the following procedures when installing the selec-
tor knob and volume knob.
1) Match the direction for the hole of the knob and the knob
spring.
2) Push the knob onto the knob spring until a click sounds.
Removing the selector knob spring and volume
knob spring
1. Lightly grasp the left and right sides of the selector knob
spring, then shift the knob spring to the left and right, little
by little, as shown in the figure.a
Note: Do not grasp the knob spring tightly.
2. Remove the selector knob spring b.
Note: Do not bring your fingers into contact with the flat
spring of the knob spring as much as possible.
3. Repeat steps 1 and 2 for the volume knob spring, to re-
move the volume knob spring c.
:
@
.
Knob spring
Encoder
Note:
Perform the following procedures when installing the selec-
tor knob spring and volume knob spring.
1) Match the direction for the knob spring and the encoder.
2)Insert the encoder onto the knob spring until a click
sounds.
Removing the mechanical stopper (K3 model only)
1. Pick up and lift the tab of a mechanical stopper using a
pair of tweezers. a
Note: Take care not to damage the packing.
2. Remove the mechanical stopper b.@
:
Removing theTX-RX unit from the chassis
1. Remove the flat cable from the connector (CN600).a
2. Remove the Speaker lead wire from the connector (CN902). b
3. Remove the PTT FPC from the connector (CN604). c
4.
Remove the VOL/SEL FPC from the connector (CN500). d
b
cd
PTT FPC
TX-RX unit
CN902
CN500
Flat cable a
CN600
CN604
5. Remove the packing efrom the SP/MIC jack.
6. Remove the 14 screws f.
7. Anchor the screw hole of the TX-RX unit using the tip of
a pair of tweezers as shown in the figure.Then lift the TX-
RX unit to remove it from the chassis. g
g
f
ff
f
f
e

NX-420
9
Removing the speaker holder
There is a space of approximately 1mm (0.04 inch) be-
tween the center part of the front glass of the speaker
holder and the surface of the Display unit. Set your finger
on the space in the center part of the front glass, then lift
and remove it.
Display unit
Speaker holder
Removing theTOP packing
1. Pull the TOP packing to the left to remove the packing that
is fit into the left groove of the chassis.a
2. Pull the TOP packing to the right to remove the packing
that is fit into the right groove of the chassis. b
3. Pull the TOP packing to the center to remove the packing
that is fit into the center groove of the chassis.c
4. Remove the TOP packing. d
Note:
Remove the packing slowly, as the packing of the selector
part might overset when the TOP packing is removed. If
the packing is turned over, return it to the normal position
using a soft tipped item (e.g., your finger).
;
@
.
:
2. Precautions for Reassembly
Mounting the chassis onto the case
1. Place the key top on the chassis. Then, fit the chassis
tightly into the groove of the key top.a
Note:
Confirm that the entire groove of the key top fits to the
chassis tightly.
2. Mount the chassis onto the case.b
Note:
• After mounting the chassis onto the case, if the 16-key
part on the key top gets stuck inside the case as shown
in the figure, return it to the normal position using a soft
tipped item (e.g., your finger). c
Prying it with a pointed metal tool such as forceps, may
damage the key top or packing.
• Confirm that the TOP packing is not caught in the An-
tenna or Volume holes of the case.
.
@
:
16-key part
Antenna of TOP packing
Volume of TOP packing
■Forming the flat cable
Form the right and left end of the flat cable as shown in
the figure. (Bend the terminal surface of the flat cable on
the inside.)
Note:When bending the flat cable, bend it squarely.There
is a possibility of disconnecting when the flat cable is bent
too much.
Flat cable
DISASSEMBLY FOR REPAIR

NX-420
10
■Changing the channel selector from 16-channel
operation to free (without LCD models only)
1. Remove the channel selector knob a. (Refer to page 8
for how to remove the channel selector knob.)
2. Remove the knob spring b. (Refer to page 8 for how to
remove the knob spring.)
3. Remove the mechanical stopper c. (Refer to page 8 for
how to remove the mechanical stopper.)
4. Reassemble the channel selector knob and knob spring
that were removed in steps 1 and 2, in their original posi-
tions.
Note: Refer to page 8 for how to install the channel selec-
tor knob and knob spring.
@
.
:
■Changing the channel selector from free opera-
tion to 16-channel (with LCD models only)
1. Remove the channel selector knob a. (Refer to page 8
for how to remove the channel selector knob.)
2. Remove the knob spring b. (Refer to page 8 for how to
remove the knob spring.)
3. Pinch the supplied mechanical stopper cusing your fin-
gers, then install it into the groove of the selector part on
the case.
4. Reassemble the channel selector knob and knob spring
that were removed in steps 1 and 2, in their original posi-
tions.
Note: Refer to page 8 for how to install the channel selec-
tor knob and knob spring.
:
@.
■Connection place of the antenna hot pin and
antenna terminal
An antenna hot pin is connected with the antenna termi-
nal at the position shown in the figure.
Confirm that the antenna hot pin has firmly come in con-
tact with the terminal when the TX-RX unit is tightened
with the screw.
Additionally, refer to the following figures for the connec-
tion place of the antenna terminal and the TX-RX unit.
TX-RX unit Antenna
terminal
Antenna
terminal
Antenna
hot pin
■Align the SP/MIC lead wire
Align the SP/MIC lead wire as shown in the figure. It is
possible to fix temporarily by interweaving the two lead
wires between the tabs (tab A and tab B) and boss of the
speaker holder.
A
B
DISASSEMBLY FOR REPAIR

NX-420
11
DISASSEMBLY FOR REPAIR
■Assembly information (Sheet/Cushion)
When “Main Parts” is changed (ordered), “Assembled Sheet/Cushion” should also be changed (ordered) together.
The Sticker and Sheet etc are non-reusable parts.It requires the new one to get the radio’s performance after repairs.
For example, when “Plastic Cabinet Assy (A02-4130-13 (without key)/A02-4132-13 (16-key))” is changed, “Sticker (B42-7417-
04)” and “Fibrous Sheet (G10-1827-04)” should be ordered and changed together because Sticker (B42-7417-04) and Fibrous
Sheet (G10-1827-04) are non-reusable.
Main Parts Assembled Sheet/ Cushion
Part Name Part Number Part Name Part Number Remark
Plastic Cabinet Assy (without key) A02-4130-13 Sticker B42-7417-04 “NEXEDGE” is printed.
(16-key) A02-4132-13 Fibrous sheet G10-1827-04
Speaker T07-0787-05 Rubber Cushion (SP) G11-4272-14
Sheet (SP) G11-4527-04
Chassis A10-4148-01
Sheet (PTT) G11-4543-04
Rubber Sheet (FET) G11-4315-14 Used for stabilizing the radiation performance
of the FET.
Sheet (Air) G11-4500-04 This sheet is put on the air vent hole. This sheet lets air through, but does not let
water through.
MIC Element T91-0673-05 Sheet (ECM) G11-4558-04

NX-420
12
1. Overview
The NX-420 is a 800MHz portable transceiver designed to
operate in the frequency range of 806 to 870MHz. The unit
consists of a receiver, transmitter, phase-locked loop (PLL)
frequency synthesizer, baseband parts, power supply, and
control circuits.
2. Frequency Configuration
The receiver is a double-conversion superheterodyne us-
ing the first intermediate frequency (IF) of 49.95MHz and the
second IF of 450kHz. Incoming signals from the antenna are
mixed with the local signal from the PLL circuit to produce
the first IF of 49.95MHz.This is then mixed with the 50.4MHz
second local oscillator output to produce the 450kHz second
IF. The transmit signal frequency is generated by the PLL
VCO, and modulated by the signal from the DSP. It is then
amplified and fed to the antenna.
CIRCUIT DESCRIPTION
ANT
SW RF AMP
1st
MIX AF
AMP
TCXO
MIC
AMP
TX
AMP
POWER
AMP
CF 450kHz
MCF
IF SYSTEM
PLL/VCO
16.8MHz
ANT
SP
MIC
TX:806~825MHz
X3
50.4MHz
Base band Circuit
TX/RX:851~870MHz
49.95MHz
TX/RX
SW
TX:806~825MHz
851~870MHz
RX 1stLo:
801.05~820.05MHz
Fig. 1 Frequency configuration
3. Receiver System
3-1. RF circuit
An incoming RF signal from the antenna terminal is
passed through the antenna switch (D102, D103, D104 and
D105) and then the band-pass filter (L217). The signal is
amplified by an RF amplifier (Q200), and passed through the
band-pass filter (L212).The resulting signal is applied to the
first mixer (IC200), where it is mixed with the first local oscil-
lator signal output from the frequency synthesizer to produce
the first IF (49.95MHz).
Fig. 2 RF and IF circuit
Q200
RF AMP Q301 IF AMP
IC200
1st MIX XF300
MCF
D102,D103
D104,D105
ANT
SW
TCXO
IC301
MIX,AGC
1st Lo CF300
L217
BPF
L212
16.8MHz
Q300
x3
2nd OSC
X400
BPF
CF301
IC 607 IC602
DSP
VOL
IC 4 IC 901 SP
ASIC
IC 601
ANT
L118

NX-420
13
3-2. IF circuit
The first IF signal is passed through a four-pole mono-
lithic crystal filter (XF300) to reject adjacent channel signals.
The filtered first IF signal is amplified by the first IF amplifier
(Q301) and then applied to the IF system IC (IC301). The
IF system IC provides a second mixer, AGC amplifier, and
RSSI (Received Signal Strength Indicator).
The second mixer mixes the first IF signal with the
50.4MHz of the second local oscillator output and produces
the second IF signal of 450kHz.
The second IF signal is passed through the ceramic filter
(CF300) to reject the adjacent channel signal. The filtered
second IF signal is amplified by the AGC amplifier in IC301.
The signal from the AGC amplifier is input to the ASIC
(IC607) through the ceramic filter (CF301).
3-3. Audio amplifier circuit
Audio processing (high-pass filter, low-pass filter, de-
emphasized and so on) at FM mode and decoding at NXDN
mode are processed by the DSP. The audio signal from
IC607 and IC601 goes through the amplifier (IC602). The
signal then goes through an electronic volume control (IC4),
and AF amplifier (IC901).
While AFSW is High, the power supply of audio power
amplifier (IC901) is activated, and the output to the speaker
turns ON.
3-4. Squelch circuit
It amplifies the demodulated noise signal from IC607 after
filtering through the LPF and HPF circuit. The amplified sig-
nal is then converted to a DC signal by the detection circuit.
The converted signal is fed back to IC607.
Fig. 3 Squelch circuit
ASQAPC
ASQDET
IC607
DET
IC1(1/2)
AMP RECT AMP
IC302
D2
Q3 ASQ
LPF
IC1(2/2)
HPF
4.Transmitter System
4-1. Audio band circuit
The signal from the microphone is amplified by IC2(2/2)
and limited by the AGC circuit which is composed of D3, D4,
Q4 and Q5. IC2 works as an anti-aliasing LPF filter.
4-2. Baseband circuit
The audio signal output from the baseband circuit is con-
verted to digital data with a sampling frequency of 48kHz.
This digital data is sent to the DSP (IC601), and voice sig-
nals of 300Hz or lower and frequencies of 3kHz or higher
are cut off and the audio range of 300Hz to 3kHz is extract-
ed. The audio signal is then pre-emphasized in FM mode
and synthesized with the signals, such as QT and DQT, as
required, and is then output from IC607. In Digital mode, the
audio signal is converted to the 4-Level FSK baseband sig-
nal and output from IC607. The DTMF and MSK baseband
signals are also generated by the DSP and output by IC607
The LPF (IC6) works as a smoothing filter. The level out-
put according to the transmit carrier is fine-adjusted accord-
ing to each modulation method.
Fig. 4 Audio band and Baseband circuit
To TX
stage
VCO
PLL IC
IC607
ASIC
IC400
IC601
DSP
LPF
IC6(1/2)
IC2(2/2)MIC MIC
AMP
AGC
D3,D4
Q4,Q5
CIRCUIT DESCRIPTION

NX-420
14
4-3.VOX
The DSP detects the audio level. If the detected level be-
comes higher than the threshold level, the VOX starts.
4-4. Drive and Final amplifier
The signal from the T/R switch (D412 is on) is amplified
by the pre-drive amplifier (Q102) to 9~10dBm. The output
of the pre-drive amplifier is amplified by the drive and final
amplifiers (Q104, Q106) to 3.0W (1.0W when the power is
low). Q104 and Q106 are MOS FETs.The output of the final
amplifier is then passed through the harmonic filter (LPF)
and antenna switch (D102, D103 are on) and applied to the
antenna terminal.
4-5. APC circuit
The APC circuit always monitors the current flowing
through the RF power amplifier (Q106) and keeps a con-
stant current.The voltage drop at R132 and R133 is caused
by the current flowing through the RF power amplifier and
this voltage is applied to the differential amplifier (IC100
1/2). IC100(2/2) compares the output voltage of IC100(1/2)
with the reference voltage from IC607, and the output of
IC100(2/2) controls the VGG of Q104 and Q100 to make
the both current constant. The change of power high/low is
carried out by the change of the reference voltage. IC106,
Q107,Q108 and Q108 are turned on and Q103 and Q105
are turned off during transmission and the APC circuit is ac-
tive.
Fig. 5 Drive and final amplifier and APC circuit
from
T/R SW (D412) Drive
AMP
Pre-Drive
AMP
Q102 Q104 Final
AMP
Q106 ANT
SW LPF
D102,D103
ANT
VGG
IC100
(1/2) IC100 (2/2)
R132
R133
+B
Reference voltage
from IC607
RFAMP
Q101
VCC from
DC SW(Q504)
5. PLL Frequency Synthesizer
5-1.TCXO (X400)
TCXO (X400) generates a reference frequency of
16.8MHz for the PLL frequency synthesizer. This reference
frequency is applied to pin 9of the PLL IC (IC400) and is
connected to the IF circuit as a 2nd osc through the Tripler
(Q300). The frequency adjustment is achieved by switching
the ratio of dividing frequency.The resolution of the adjusting
frequency is approximately 4Hz.
5-2.VCO
There are two VCOs (VCO-1 and VCO-2).
VCO-1 (Q401) generates the 1st local signal for the re-
ceiver and a carrier for the transmitter.
VCO-2 (Q402) generates a carrier for the transmitter of TA
(Talk Around).
The oscillation frequency of the VCO is half of the carrier
or 1st local signal. The VCO oscillates from 403 to 435MHz
during transmit, and from 400.525 to 410.025MHz during
reception.
The VCO oscillation frequency is determined by one sys-
tem of operation switching terminal “/T_R” and two systems
of voltage control terminals “CV” and “ASSIST”.
The operation switching terminal, “/T_R”, is controlled by
the control line (/T_R) output from the ASIC (IC607).
When the /T_R logic is low, VCO-2 is activated, and when
the /T_R logic is high, VCO-1 is activated.
The voltage control terminals, “CV” and “ASSIST”, are
controlled by the PLL IC (IC400) and ASIC (IC607) and the
output frequency changes continuously according to the
applied voltage. For the modulation input terminal, “VCO_
MOD”, the output frequency changes according to the ap-
plied voltage.This is used to modulate the VCO output.
5-3. PLL IC (IC400)
The PLL IC compares the differences in phases of the
VCO oscillation frequency and the TCXO reference fre-
quency, returns the difference to the VCO CV terminal and
realizes the “Phase Locked Loop” for the return control. This
allows the VCO oscillation frequency to accurately match
(lock) the desired frequency.
CIRCUIT DESCRIPTION

NX-420
15
When the frequency is controlled by the PLL, the frequen-
cy convergence time increases as the frequency difference
increases when the set frequency is changed. To supple-
ment this, the ASIC is used before control by the PLL IC
to bring the VCO oscillation frequency close to the desired
frequency. As a result, the VCO CV voltage does not change
and is always stable at approximately 2.5V.
The desired frequency is set for the PLL IC by the ASIC
(IC607) through the 3-line “SDO1”, “PCK_RF”, “/PCS_RF”
serial bus.Whether the PLL IC is locked or not is monitored
by the ASIC through the “PLD” signal line. If the VCO is not
the desired frequency (unlock), the “PLD” logic is low.
“PLLMOD” receives the modulation data from the DSP
(IC601).
5-4. Local Switch (D411, D412)
The connection destination of the signal output from the
buffer amplifier (Q408) is changed with the diode switch
(D412) that is controlled by the transmission power supply,
50T, and the diode switch (D411) that is controlled by the
receive power supply, 50R. If the 50T logic is high, it is con-
nected to a send-side RF amplifier (Q101). If the 50T logic is
low, it is connected to a receive-side mixer (IC200).
Fig. 6 PLL block diagram
Q401,Q402
VCO_MOD
CV
BUF
SD01,/PCS_RF
PCK_RF,PLD
/T_R
TX/RX
SW
D411,D412
Ripple
filter
Q403
50C
X400
VCO 1
IC401
VCO 2
BUF
IC402
PLL IC
ASIC
DSP TCXO
IC601
Q404
Q406
X2
Q405
BUF
Q407
BUF
Q408
BUF
IC6
IC607
ASIC
PLL MOD
6. Control Circuit
The control circuit consists of CPU in ASIC (IC607) and
its peripheral circuits.CPU mainly performs the following;
1) Switching between transmission and reception by PTT
signal input.
2) Reading system, zone, 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 decode data input.
6-1. ASIC
The ASIC (IC607) is a 32-bit RISC processor, equipped
with peripheral function and ADC/DAC.
This ASIC operates at 18.432MHz clock and 3.3V/1.5V
DC. It controls the flash memory, SRAM, DSP, the receive
circuit, the transmitter circuit, the control circuit, and the dis-
play circuit and transfers data to or from an external device.
6-2. Memory Circuit
The memory circuit consists of the ASIC (IC607), the
SRAM (IC603), and the flash memory (IC600). The flash
memory has a capacity of 32M-bit that contains the trans-
ceiver control program for the ASIC and stores the data. It
also stores the data for transceiver channels and operating
parameters that are written by the FPU. This program can
be easily written from external devices.The SRAM has a ca-
pacity of 1M-bit that contains work area and data area.
Flash memory
Note :
• The flash memory stores the data that is written by the
FPU (KPG-141D), tuning data (Deviation, Squelch, etc.)
,and firmware program (User mode, Test mode, Tuning
mode, etc.). This data must be rewritten when replacing
the flash memory.
SRAM (Static memory)
Note :
• The SRAM has temporary data area and work area.
CIRCUIT DESCRIPTION

NX-420
16
6-3. LCD
The LCD is controlled using the 4 serial line from ASIC
(IC607).
6-4. Key Detection Circuit (K3 model only)
Keys are detected using the LCD controller driver IC (IC8).
If a pressed key is detected by IC8, it is informed to IC607
through the serial line.
6-5. Low Battery Warning
The battery voltage is divided using R500 and R502 and
is detected by the ASIC (IC607). When the battery voltage
falls below the voltage set by the Low battery warning ad-
justment, the red LED blinks 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 stops.
Low battery warning Battery condition
The red LED blinks during
transmission. The battery voltage is low but the transceiver is still usable.
The red LED blinks and the
warning tone beeps while the
PTT switch is pressed.
The battery voltage is low and
the transceiver is not usable to
make calls.
6-6. DSP
The DSP circuit consists of a DSP (IC601) and processes
the baseband signal.The DSP operates on an external clock
of 18.432MHz (the same as the IC607), the I/O section oper-
ates at 3.3V and the core section operates at 1.5V.
The DSP carries out the following processes:
• 4 Level FSK processing
• Analog FM pre-emphasis/de-emphasis
• Vocoder processing between audio codec and modulation/
demodulation
• CAI processing, such as error correction encoding
• QT/DQT encoding/decoding
• LTR encoding/decoding
• DTMF encoding/decoding
• MSK encoding/decoding
• Compressor/expander processing
• Voice scrambler processing
• Transmit/receive audio filtering processing
• Microphone amplifier AGC processing
• Audio mute processing
• Modulation level processing
CIRCUIT DESCRIPTION
7. Power Supply Circuit
The battery voltage (+B) is provided from the battery ter-
minal on the TX-RX unit (X57). The battery voltage passes
through the 2.5A fuse (F500), and goes to the RF final am-
plifier, AVR ICs (IC504, IC900), DC/DC converter (IC505),
and voltage detector IC (IC506). The voltage detector
watches the battery voltage. If the battery voltage is 5.6V or
higher, the detector outputs High.
When the VOL SW is turned on, SB1 becomes high (bat-
tery voltage). DC/DC (IC505) operates if both SB1 and the
output of the detector are high. IC505 outputs 3.8V and ac-
tivates IC501 (33M), IC502 (15M), IC500 (33A) and IC503
(33C). As a result, ASIC and DSP operate.
The SBC signal becomes High after the ASIC operates,
IC504 (50C), IC900 (50V) and Q500 (SB2) are turned on.
When the /SAVE signal becomes High, Q503 (50C) oper-
ates.Switches (Q504, Q505) are controlled by the ASIC.
Q504 (50T) is turned on in transmit mode. Q505 (50R) is
turned on in receive mode.
When the VOL SW is turned off, the /PSW signal be-
comes
Low. After detecting the /PSW signal, the ASIC changes
the SBC signal to Low.
8. Signaling Circuit
8-1. Encode (QT/DQT/LTR/DTMF/MSK)
Each signaling data signal of QT, DQT, LTR, DTMF and
MSK is generated by the DSP circuit, superimposed on a
modulation signal and output from IC607.
Each deviation of the TX QT, DQT, LTR, DTMF and MSK
tone is adjusted by changing the output level of IC601 and
the resulting signal is routed to the VCO and PLL.
8-2. Decode (QT/DQT/LTR/DTMF/MSK)
The audio signal is removed from the FM detection signal
sent to the DSP circuit and the resulting signal is decoded.
9. Compander Circuit
The term “compander” means compressor and expander.
The compander reduces noise by utilizing a compressor
and an expander.The transceiver contains a DSP (IC601) to
perform this operation. The transceiver compander can be
turned on or off using the FPU.

NX-420
17
Fig. 7 Power supply circuit
F500
2.5A F900
1.0A
VOL/SW
+B
TX-RX unit
Q902
SW
IC900
50V
IC506
5.6V Det
IC505
38M IC500 33A
IC501
33M
IC502
15M
IC503
33C
IC504
50C
Q500
SB2
Q504
50T
Q505
50R
Q503
50CS Ripple
filter
IC8
LCD driver
ASIC
IC607
Final AMP, APC
AFPA
2-pin Jack
DSP, FLASH, SRAM
DSP
PLL, TCXO
ASSIST circuit
TX circuit
RX circuit
PLL, fin
VCO
AF circuit
AF circuit, DAC
SQL circuit
LED
/PSW
/BINT
Display unit
CN600
CN5
CIRCUIT DESCRIPTION

NX-420
18
Display unit (X54-3760-10) K3 type
Ref. No. Part Name Description
IC1 IC ASQ BPF/ASQ BPF
IC2 IC OP AMP(AF LPF/MIC AMP)
IC4 IC D/A converter
IC6 IC OP AMP(VCO_MOD/VREF)
IC8 IC LCD driver
Q1 Transistor TX/BUSY LED switch
Q2 FET SQL switch
Q3 Transistor SQL noise amplifier
Q4,5 Transistor MIC AGC
Q6~8 Transistor KEY backlight sw
D1 LED TX/BUSY LED
D2 Diode Noise detector
D3,4 Diode AGC detector
D7~14 LED KEY backlight
D15,16 Diode KEY control
D18,19LED LCD backlight
COMPONENTS DESCRIPTION
TX-RX unit (X57-8370-10)
Ref No. Part Name Description
IC100 IC APC control
IC200 IC 1st mixer
IC300 IC Buffer amplifire (DET)
IC301 IC FM system
IC302 IC DC amplifire (ASQ/RSSI)
IC400 IC PLL system
IC401 IC DC amplifire (Assist)
IC402 IC DC amplifire (CV/APC)
IC500 IC Voltage regulator (33A)
IC501 IC Voltage regulator (33M)
IC502 IC Voltage regulator (15M)
IC503 IC Voltage regulator (33C)
IC504 IC Voltage regulator (50C)
IC505 IC DC/DC converter (38M)
IC506 IC Reset
IC600 IC Frash memory
IC601 IC DSP
IC602 IC Sum amplifire
IC603 IC SRAM
IC604 IC Reset
IC605 IC Motion sensor
IC606 IC Buffer amplifire
IC607 IC ASIC
IC608,609IC And gate (2 Input)
IC900 IC Voltage regulator (50V)
IC901 IC Audio power amplifire
Q101 Transistor RF amplifire
Q102 FET Pre-drive amplifire
Q103 Transistor DC switch (FET BIAS)
Q104 FET Drive amplifire
Q105 FET DC switch (APC)
Q106 FET Final amplifire
Q107 Transistor DC switch (APC)
Q108 FET Switch control (BIAS)
Q109FET Switch control (APC)
Q200 FET RF amplifire(LNA)
Q300 Transistor Tripler
Q301 Transistor 1st IF amplifire
Q401 FET VCO (TX/RX)
Q402 FET VCO (TA)
Display unit (X54-3760-12) K type
Ref. No. Part Name Description
IC1 IC ASQ BPF/ASQ BPF
IC2 IC OP AMP(AF LPF/MIC AMP)
IC4 IC D/A converter
IC6 IC OP AMP(VCO_MOD/VREF)
IC8 IC LCD driver
Q1 Transistor TX/BUSY LED switch
Q2 FET SQL switch
Q3 Transistor SQL noise amplifier
Q4,5 Transistor MIC AGC
Q6~8 Transistor KEY backlight sw
D1 LED TX/BUSY LED
D2 Diode Noise detector
D3,4 Diode AGC detector

NX-420
19
COMPONENTS DESCRIPTION
Ref No. Part Name Description
Q403 Transistor Ripple Filter
Q404 FET Switch control (Q406)
Q405 Transistor Doubler
Q406 FET DC switch (VCO)
Q407 Transistor Buffer amplifire
Q408 Transistor RF amplifire
Q500 FET DC switch (SB2)
Q501 FET Switch control (Q500)
Q502 Transistor Switch control (Q504)
Q503 FET DC switch (50CS)
Q504 Transistor DC switch (50T)
Q505 Transistor DC switch (50R)
Q506,507 FET Level converter
Q508 Transistor Switch control (SB1)
Q509Transistor Load
Q600 FET DC switch (SB2)
Q900 Transistor DC switch (SB2)
Q901 Transistor Switch control (Q902)
Q902 Transistor DC switch (AF AMP)
Q903 FET Switch control (AF mute)
Q904 FET AF mute switch
Q905 FET Level converter
Q906 FET AF mute switch
D100 Zener diode Over voltage protection
D102-105 Diode Antenna switch
D200 Diode Limitter
D400 Diode Limitter
D402,403 Variable capacitnce
diode VCO frequency control
D404-407 Variable capacitnce
diode VCO assist control
D408,409Variable capacitnce
diode TX modulation
D410 Diode Speed up
D411,412 Diode RF switch
D500 Diode Receive protection (+B)
D501 Diode Speed up
D502,503 Diode DC/DC converter
D505 Diode Bypass
D506 Diode Receive current prevention
D900,901 Diode Receive current prevention

NX-420
20
New Parts. indicates safety critical components.
Parts without Parts No. are not supplied.
Les articles non mentionnes dans le Parts No. ne sont pas fournis.
Teile ohne Parts No. werden nicht geliefert.
L: Scandinavia K: USA P: Canada
Y: PX (Far East, Hawaii) T: England E: Europe
C : China X: Australia M: Other Areas
Ref. No. Address Parts No. Description Desti-
nation
New
parts
Ref. No. Address Parts No. Description Desti-
nation
New
parts
PARTS LIST
NX-420
DISPLAY UNIT (X54-3760-XX)
1 2B A02-4130-13 PLASTIC CABINET ASSY K
3 2B A02-4132-13 PLASTIC CABINET ASSY(16KEY) K3
4 1B A10-4148-01 CHASSIS
6 3A B01-0694-13 ESCUTCHEON
7 1C B09-0686-03 CAP (ACCESSORY)
8 1A B11-1869-04 ILLUMINATION GUIDE(TX/BUSY)
91A B11-1890-04 FILTER(LCD) K3
10 1A B11-1891-02 ILLUMINATION GUIDE(LCD) K3
11 1A B38-0935-05 LCD K3
12 1A B42-7417-04 STICKER
13 2D
B62-2470-00 INSTRUCTION MANUAL (ACCESSORY)
16 1B,1D D32-0454-04 STOPPER(16CH)
18 3A E04-0467-15 RF COAXIAL RECEPTACLE(SMA)
192A E23-1363-04 TERMINAL(ANT)
20 1A E29-1232-05 INTER CONNECTOR(LCD) K3
21 1A E37-1532-15 LEAD WIRE WITH CONNECTOR
22 1A E37-1537-05 FLAT CABLE(X57-X54)
23 2A E72-0435-03 TERMINAL BLOCK
26 1A G02-1864-04 EARTH SPRING(X54)
27 1B G09-0443-04 KNOB SPRING(VOL/SEL)
28 1B G10-1827-04 FIBROUS SHEET(SP)
291A G11-4272-14 RUBBER CUSHION(SP)
30 3A G11-4315-14 SHEET(Q106)
31 1A G11-4335-14 SHEET(LCD) K3
32 1A G11-4368-04 SHEET(TERMINAL BLOCK)
33 3A G11-4500-04 SHEET(AIR)
34 1A G11-4527-04 SHEET(SP)
35 3A G11-4543-04 SHEET(PTT)
36 1A G11-4558-04 SHEET(ECM)
37 3A G11-4561-04 SHEET(TX/BUSY)
38 1A G11-4562-04 SHEET(SP HOLDER)
391A G13-2068-04 CUSHION(VOL/SEL)
40 2A G13-2220-04 CUSHION(X54)
41 2A G13-2249-04 CUSHION
42 3A G53-1603-04 PACKING(SMA)
43 2B G53-1862-02 PACKING(TOP/BATT)
44 2B G53-1863-01 PACKING K
45 1B G53-1865-11 PACKING(16 KEY) K3
46 1B G53-1866-04 PACKING(TERMINAL)
47 1A G53-1885-03 PACKING(JACK)
48 1C H12-4312-02 PACKING FIXTURE
493C
H52-2594-02 ITEM CARTON CASE
51 1D J19-5483-23 HOLDER (ACCESSORY)
52 1A J19-5547-01 HOLDER(FG-SP)
53 1A J21-8631-03 MOUNTING HARDWARE(LCD) K3
54 1D J29-0701-25 BELT CLIP (ACCESSORY)
55 1A J69-0370-04 RING(JACK)
56 3A J87-0027-05 FPC(PTT)
57 2A J87-0040-05 FPC(VOL/SEL)
58 1A K29-9485-13 KNOB(VOLUME)
591B K29-9486-13 KNOB(SELECTOR)
60 1B K29-9500-03 KNOB(PTT)
61 1B K29-9501-03 BUTTON KNOB(PTT)
A 3A N09-2438-05 BINDING HEAD SCREW(ANT)
B 3A N09-6608-05 SPECIAL SCREW
C 3A N14-0864-04 CIRCULAR NUT(VOLUME)
D 3A N14-0865-04 CIRCULAR NUT(SELECTOR)
E 3A N30-3006-43 PAN HEAD MACHINE SCREW
F
1A,2A,3A N83-2005-48 PAN HEAD TAPTITE SCREW(X54/57)
VR1 3A R31-0685-05 VARIABLE RESISTOR(VOLUME)
S101 2A S60-0448-05 ROTARY SWITCH(SELECTOR)
65 1A T07-0787-05 SPEAKER
66 1D
T90-1114-05 WHIP ANTENNA (ACCESSORY)
X57-8370-11 TX-RX UNIT(FOR SERVICE)
D1 B30-2278-05 LED(RED/YELLOW)
D7 -14 B30-2337-05 LED(YELLOW) K3
D18 ,19B30-2210-05 LED K3
C1 CK73HB1H471K CHIP C 470PF K
C2 CK73HB1H681K CHIP C 680PF K
C3 CC73HCH1H270J CHIP C 27PF J
C4 CK73HB1H471K CHIP C 470PF K
C5 CK73HB1A104K CHIP C 0.10UF K
C6 CK73HB1H102K CHIP C 1000PF K
C7 ,8 CC73HCH1H470J CHIP C 47PF J
C10 CC73HCH1H101J CHIP C 100PF J
C11 CK73HB1H681K CHIP C 680PF K
C13 CC73HCH1H101J CHIP C 100PF J
C15 CK73HB1E103K CHIP C 0.010UF K
C16 CK73HB1H102K CHIP C 1000PF K
C19CK73HB1A104K CHIP C 0.10UF K
C20 CK73HB1H102K CHIP C 1000PF K
C21 CK73HB1E103K CHIP C 0.010UF K
C22 CK73HB1A224K CHIP C 0.22UF K
C23 CC73HCH1H470J CHIP C 47PF J
C25 CK73HB1A224K CHIP C 0.22UF K
C26 CC73HCH1H470J CHIP C 47PF J
C28 ,29CC73HCH1H470J CHIP C 47PF J
C30 CK73HB0J105K CHIP C 1.0UF K
C31 CC73HCH1H470J CHIP C 47PF J
C32 CK73HB1H122K CHIP C 1200PF K
C33 ,34 CC73HCH1H470J CHIP C 47PF J
C35 CK73HB1A104K CHIP C 0.10UF K
C36 CC73HCH1H470J CHIP C 47PF J
C37 CK73HB1H472K CHIP C 4700PF K
C38 CC73HCH1H181J CHIP C 180PF J
C39CK73HB1A104K CHIP C 0.10UF K
C40 CC73HCH1H470J CHIP C 47PF J
NX-420
DISPLAY UNIT (X54-3760-XX) -10: K3 -12: K,