Radio Shack HTX-400 User manual

Service
HTX-400
MINI HANDHELD 70cm FM
AMATEUR TRANSCEIVER
Catalog Number : 19-1104
CONTENTS
page
Specifications----------------------------------------------------------------------------------------------- 1
Theory of Operation --------------------------------------------------------------------------------------- 2
Block Diagram ---------------------------------------------------------------------------------------------- 8
Alignment Instructions ------------------------------------------------------------------------------------ 9
Test Equipment Set-Up --------------------------------------------------------------------------------- 12
Semiconductor Lead Identification and IC Internal Diagram ----------------------------------15
PCB Views ------------------------------------------------------------------------------------------------- 25
Wiring Diagram -------------------------------------------------------------------------------------------29
Troubleshooting Chart ----------------------------------------------------------------------------------30
Exploded View of Unit ----------------------------------------------------------------------------------31
Whole PartsList ------------------------------------------------------------------------------------------32
Schematic Diagrams------------------------------------------------------------------------------------40
¨Ï 1999Tandy Corporation
All Rights Reserved.
RadioShack is a registered trademark used by Tandy Corporation

1
SPECIFICATIONS
1. GENERAL
FREQUENCY :
RX -------------------------------------------------------- 420-470 MHz
TX --------------------------------------------------------- 430-470 MHz
FREQUENCY GENERATION ------------------------PLL SYNTHESIZER
FREQUENCY STABILITY ---------------------------- ¡¾5 PPM
OPERATING TEMPERATURE ---------------------- 14¢ª TO 131¢ªF(-10¡É TO 55¡É)
POWER SOURCE -------------------------------------- DC 3.0V TO 9V
MODULATION -------------------------------------------- F3E
IMPEDANCE ----------------------------------------------50 ohm
DIMENSIONS (HWD) ----------------------------------- 2 1/4¡¿3 3/8¡¿11/16 inches
85¡¿58¡¿26.5 mm
WEIGHT (without batteries) ---------------------------4.2 oz (120g)
2. RECEIVER SECTION
CIRCUIT TYPE ------------------------------------------- DUAL CONVERSION,SUPERHETERODYNE
IF FREQUENCY :
1st IF ----------------------------------------------------- 30.85 MHz
2nd IF ---------------------------------------------------- 450 KHz
SENSITIVITY ---------------------------------------------- 0.22¥ìV for 12dB SINAD
SELECTIVITY --------------------------------------------- 50 dB Min.
SPURIOUS & IMAGE REJECTION ----------------- 40 dB Min.
INTERMODULATION ----------------------------------- 50 dB Min.
DISTORTION --------------------------------------------- 10 % Max.
S/N RATIO ------------------------------------------------- 40 dB Min.
AUDIO OUTPUT @10%THD ------------------------- 80 mW 16 Ohm, BTL
3. TRANSMITTER SECTION
POWER OUTPUT --------------------------------------- 300 mW
DISTORTION ----------------------------------------------10 %
DEVIATION ----------------------------------------------- ¡¾5.2 KHz
S/N RATIO ------------------------------------------------- 35 dB
CURRENT DRAIN ---------------------------------------- 600 mA

2
THEORY OF OPERATION
1. SEMICONDUCTORS AND FUNCTION
1.1 IC COMPLEMENT
REF.NO TYPE MANUFACTURER FUNCTION
IC601
IC801
IC802
IC806
IC501
IC3
IC805
IC401
IC803
IC807
IC804
IC808
TK11230AM
TMP87PP21DF
24LC16B
NJM2902V
LV2105V
NJM2073M
FX465DF
TA31136FN
TK11230AM
NJM2904V
XC6371A350PR
AS2801M
TOKO
THOSHIBA
PRO-CHIPS
JRC
SANYO
JRC
MX-COM
TOSHIBA
TOKO
JRC
TORREX
ALPHA
IC-REGULATOR
CPU IC
EEPROM
MIC AMP
PLL IC
AUDIO POWER AMP
CTCSS ENCODER
IC-IF
IC-REGULATOR
TONE AMP
D/D CONVERTOR
IC-REGULATOR
1.2 TRANSISTOR COMPLEMENT
REF.NO TYPE MANUFACTURER FUNCTION
Q101
Q102
Q103
Q104
Q105
Q106
Q201
Q202
Q203
Q305
Q304
Q302
Q303
Q301
Q501
Q601
Q602
Q603
Q604
Q606
Q607
Q801
Q805
Q804
Q810
Q107
MRF9242T1
MMBR951LT1
MMBR951LT1
2SC3356
2SC3356
KTA1001S
2SC4226
2SC4226
KTC4081
KRC104S
2SC3356
MMBR951
MMBR951
KTC3875
KRC410
KRA310
KRA310
KRA310
KRA310
KRC404
KTA2015
KTC3875
KRC104
KRA110
2SJ144
KRC401
MOTOROLA
MOTOROLA
MOTOROLA
NEC
NEC
KEC
NEC
NEC
KEC
KEC
NEC
MOTOROLA
MOTOROLA
KEC
KEC
KEC
KEC
NEC
KEC
KEC
KEC
KEC
KEC
KEC
NEC
KEC
FINNAL RF AMP
DRIVER AMP
PREDRIVER AMP
BUFFER
BUFFER
TX S/W
1'ST AMP
1'ST MIXER
IF AMP
VCO R/TX S/W
VCO OSC
VCO BUFFER
VCO BUFFER
VCO REG
PLL LOCK S/W
RX B+ S/W
SAVE B+ S/W
TX EN1 B+ S/W
TX EN2 B+ S/W
AUDIO MUTE S/W
AUDIO B+ S/W
LAMP S/W
RESET S/W
PTT S/W
RX MUTE S/W
TX S/W

3
1.3 DIODE COMPLEMENT
REF.NO TYPE MANUFACTURER FUNCTION
D804-805
D807
D806
D804A
D830
D802
ZD803
LED801-802
D201-202
D101
D102
D303
D302
D601
D401
D301
1N4001(M2)
1N4001(M2)
RB471E
KDS187
MA77
KDS187
ZD7.5Y
LED
MA77
MA77
MA862
KDS114
KV1832
KDS181
MMBD101
1SV229
ROHM
ROHM
ROHM
KEC
PANASONIC
KEC
KEC
EVERLIGHT
PANASONIC
PANASONIC
PANASONIC
KEC
TOKO
KEC
MOTOROLA
NEC
REVERSE B+ PROTECT
REG REVERSE PROTECT
D/D CON S/W
CTCSS COMPARATOR
CLOCK SHIFT S/W
MODEL SELECTOR
PTT S/W
BACKLIGHT LED
RX LPF S/W
TX LPF S/W
R/TX LOCAL S/W
R/TX VCO S/W
VCO OSC
RX B+ S/W
SQ DET
DEV. VARICAP
¡ØREMARKS.
KEC :KOREA ELECTRONICS CO., LTD.
ROHM :ROHM KOREA CORP.
TOSHIBA :TOSHIBA CO. LTD
MOTOROLA : MOTOROLA CO. LTD
JRC : NEW JAPAN RADIO CO. LTD
SANYO :SANYO ELECTRIC CO., LTD.
TOKO : JAPAN TOKO CO., LTD
PRO-CHIPS : JAPAN MICROCHIP CO., LTD
TORREX : JAPAN TORREX CO., LTD
EVERLIGHT : TAIWAN EVERLIGHT CO., LTD
PHILLIPS : TAIWAN PHILLIPS CO., LTD
ALPHA : ALPHA SEMICONDUCTOR CO., LTD
MX-COM : MX¡¤ COM, INC.
PANASONIC : MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD

4
2. DESCRIPTION OF FREQUENCY DETERMINING
AND STABILIZING CIRCUIT
2.1 INTRODUCTION
THE FREQUENCIES FOR TRANSMITTER AND RECEIVER LOCAL FREQUENCIES ARE ALL
DRIVED FROM ASINGLE 15.2[MHz] VCTCXO BY MEANS OF APHASE LOCKED LOOP.
THE FIRST LOCAL OSCILLATOR FREQUENCIES ARE 389.15 [MHz] TO 439.15 [MHz].
THE SECOND LOCAL FREQUENCY IS FIXED AT 30.4 [MHz] TO GENERATE SECOND IF 450[KHz].
DURING TRANSMISSION,THE VCO OF THE PLL OPERATES 420.000 [MHz] TO 470.000[MHz].
Q301 Q104 TO TRANSMITTER
VCO BUFFER AMP
420.000 [MHz] 420.000 [MHz]
¡- 470.000 [MHz] ¡- 470.000 [MHz]
THE VCO OPERATING FREQUENCY FOR THE RECEIVER IS 389.15 [MHz] TO 439.15 [MHz].
IT IS INJECTED THROUGH THE BUFFER AMP Q302 INTO THE FIRST TR MIXER Q202
2.2 DESCRIPTIONS OF EACH BLOCK
(1) INTRODUCTION
THE SYNTHESIZER CONSISTS OF THE FOLLOWING
COMPONENTS :PLL IC (IC501), VCTCXO (MODULE1), VCO, VARICAP DIODE (D302)
IC501 IS ACMOS LSI THAT INCLUDES PRESCALLER. Q304,L303, L302, D302,D301, C322,
C319,C316, C315 ARE CLAPP OSCILLATOR CIRCUIT TO OPERATE AS A VCO OF IC501.
Q301IS ASWITCHING TRANSISTOR TO CONNECT OR DISCONNECT THE TUNING
CAPACITOR IN THE VCO OSCILLATOR TANK CIRCUIT FOR TRANSMITTER OR RECEIVER.
Q104 AND Q105 WORK AS ABUFFER AMP FOR RX LOCAL FREQUENCIES AND TX CARRIER
GENERATING FREQUENCIES.
(2) REFERENCE FREQUENCY
THE CRYSTAL, VCTCXO MODULE1(15.2[MHz] )AND OTHER COMPONENTS AT PIN 1AND 16
OF IC501 CAN MAKE AREFERENCE FREQUENCY OSCILLATOR WITH INTERNAL AMPLIFIER.
(3) VCO
Q302AND SURROUNDING PARTS FORM ACLAPP OSCILLATOR WHICH WORKS AS AVCO OF
IC501 WITH APPROPRIATE CONTROL VOLTAGE ON D302,THE VCO CAN OSCILLATE OVER
THE REQUIRED RANGE OF 389.15 [MHz] TO 470.00 [MHz].

5
(4) PROGRAMMABLE DIVIDER AND ITS CONTROL
THE PROGRAMMABLE INPUTS FOR EACH CHANNEL ARE SET INSIDE IC801.
EACH INPUT SIGNAL TO CONTROL THE PLL IC501 IS DONE WITH THE PROVIDED (CPU IC
801) KEY MATRIX INPUT PINS -PIN25 TO PIN28 AND FOR EACH KEY MATRIX INPUT, AN
INTERNAL CODE CONVERT EPROM PROVIDES THE APPROPRIATE BINARY CONTROL TO IC501
FOR THAT CHANNEL.
AN ADDITIONAL BIT IS REQUIRED AT PIN 42OF IC801 TO ALLOW THE ROM TO RECOGNIZE
WHETHER THE STATUS IS TX OR RX.
DURING TRANSMISSION,THE PUSH TO TALK SWITCH MAKES PIN 42 OF CPU IC HI.
THE OUTPUT OF IC501 ISFED TO THE PHASE DETECTOR TO COMPARE IT WITH THE 6.25
[KHz] REFERENCE FREQUENCY INSIDE.
(5) PHASE DETECTOR AND VCO CONTROL
THE PHASE DETECTOR IS ADIGITAL PHASE COMPARATOR WHICH COMPARES THE PHASE
OF THE REFERENCE SIGNAL WITH PROGRAMMABLE DIVIDER OUTPUT SQUARE WAVES AND
DEVELOPS ASERIES OF PULSES WHOSE DC LEVEL DEPENDS ON THE PHASE ERROR OF
EACH SIGNAL.
THE PHASE DETECTOR PULSE OUTPUT IS FED TO AN ACTIVE LOW PASS FILTER, AND FED
TO VARICAP D302WHICH CONTROLSTHE VCO FREQUENCY.
(6) TRANSMITTER /RECEIVER BUFFER AMP
OUTPUT SIGNAL OF Q302IS FED INTO THE BUFFER AMP Q105, Q104 TO INCREASE THE
STRENGTH OF TX CARRIER FREQUENCY AND 1’st LOCAL FREQUENCIES.
(7) SWITCHING OF TUNING CAPACITOR IN VCO
THE VCO CIRCUIT MUST TUNE WITH AWIDE RANGE OF FREQUENCIES 420.000¡-470.000
[MHz] FOR TRANSMITTER AND 389.150¡-439.150 [MHz] FOR RECEIVER.
TO COMPLY ABOVE RANGE OF VCO, THE TUNING CAPACITANCE SHOULD BE SWITCHED
FOR TRANSMISSION OR RECEPTION.
THE TUNING CIRCUIT CONSISTS OF Q304,L303,L302,D302,D301, C322, C319, C316, C315
WHEN THE VCO IS WORKING AS ARX,Q305BECOMES OFF.
SO, D303 AND C317 MAKE TUNING FUNCTION WHEN TX Q301BECOMES ON.
SO, L302 AND THE PARALLEL CAPACITANCE OF D302, C322 AND C319 MAKE TUNING
FUNCTION.

6
(8) RECEIVER LOCAL OSCILLATOR OUTPUTS
1’st MIXER :THE OUTPUT SIGNALS OF Q104 IS INJECTED TO THE SOURCES OF 1st MIXER
Q203 IN THE 1’st IF MIXER SECTION.
2’nd MIXER :THE OUTPUT OF 30.4 [MHz] OSCILLATOR CIRCUIT WITH X401 IS INJECTED
INTO IC401. INCOMING IF SIGNAL AND 30.85[MHz] SIGNAL ARE MIXED INSIDE THE IF IC TO
EXTRACT 2’nd IF SIGNAL 450 [KHz].
FM SIGNALS ARE RECOVERED WITH ENVELOPE DETECTOR.
2.3 FREQUENCY STABILITY
LET :Fo=CRYSTAL OSCILLATOR FREQUENCY
Fr=PHASE DETECTOR REFERENCE FREQUENCY
Fvco=VCO FREQUENCY
Ft=TRANSMIT FREQUENCY
THEN :Fr=Fo/ 2048
AND UNDER LOCKED CONDITIONS :Fr =Fvco /N
Where ,"N" IS THE DIVIDE RATIO OF PROGRAMMABLE DIVIDER.
THEN :Fvco =NXFr
FROM WHICH IT CAN BE SEEN, THE PERCENTAGE ERROR IN Ft IS THE SAME AS THE
PERCENTAGE ERROR IN Fo.
THE STABILITY OF THE CRYSTAL OSCILLATOR IS DETERMINED PRIMARILY BY THE CRYSTAL
ITSELF AND HAVING PASSIVE COMPONENTS OF THE OSCILLATOR.
THE CHOICE OF CRYSTAL AND COMPONENTS IS SUCH THAT THE REQUIRED FREQUENCY
STABILITY IS MAINTAINED OVER THE REQUIRED VOLTAGE AND TEMPERATURE RANGE.
2.4 DESCRIPTION OF OTHER CIRCUITS
TRANSMITTER
(1) RF AMPLIFICATION
THE OUTPUT OF BUFFER AMP Q104 IS FED THROUGH TUNING C126 TO THE BASE OF PRE
DRIVER AMP Q103.
THE OUTPUT IS THEN SUPPLIED THROUGH CAPACITOR C123 TO RF DRIVER AMP Q102.
THE OUTPUT OF Q102 IS SPLITTED WITH TUNING CIRCUIT L111,C119 AND GOES TO THE
BASE OF FINAL RF AMP Q101.
THE OUTPUT OF Q101IS SUPPLIED TO THE ANTENNA THROUGH L-C TUNING CIRCUIT.

7
(2) CIRCUIT FOR SUPPRESSION OF SPURIOUS RADIATION
THE TUNING CIRCUIT BETWEEN THE OUTPUT OF FINAL AMP Q101 AND ANTENNA, 4-STAGE
"PHI TYPE" NETWORK L101, L102, L103, L104, L105, L106, L107, C101, C102, C103, C104, C105,
C106 SERVES AS A SPURIOUS RADIATION SUPPRESSOR.
THIS NETWORK ALSO SERVES TO MATCH THE IMPEDANCE BETWEEN TX FINAL POWER AMP
Q101 AND THE ANTENNA.
(3) MAXIMUM MODULATION CONTROL
MODULATION SIGNALS ARE FILTERED WITH RC NETWORK AND GO TO THE AUDIO AMP
TO MAKE IT TO NOMINAL SIGNAL LEVEL TO ACHIEVE WANTED MODULATION.
IC806PIN13 AND CORRESPONDING LEVEL LIMITING CIRCUIT CONTROL INCOMING AUDIO
SIGNAL WITH RV802.
ADJUSTING RV802 SHALL NOT EXCEED ¡¾5.0KHz DEVATION UNDER.1KHZ AF 20dB UP
FROM 3KHZ DEVATION LEVEL INPUT.
RECEIVER
(1) RF AMP Q201 AMPLIFY RF SIGNAL FROM ANTENNA. THE AMPLIFIED RF SIGNAL IS FED
THROUGH TUNING BAND PASS FILTER SAW1, SAW2 TO THE BASE OF MIXER AMP Q202.
ALSO VCO SOURCE'S FREQUENCY 30.85MHz LOW THAN THE FREQUENCY OF EACH
CHANNEL IS SUPPLIED TO MIXER.
(2) THE SOURCE OF 30.85MHz FREQUENCY PASSED TUNING COIL L209 AND C217 IS FED
THROUGH MCF201/MCF202 TO IF AMP Q204.
(3) THE 450KHz FREQUENCY SIGNAL IS PRODUCED FROM IC401 BY MIXING THE OUTPUT
SOURCE OF MCF201/MCF202 30.85MHz FILTER AND THE SOURCE OF 30.4MHz
FREQUENCY FROM CRYSTAL OSCILLATOR X401.
(4) IC401 IS A FM DETECTOR WHICH PRODUCES AUDIO SIGNAL.THE AUDIO SIGNAL (IC401
PIN 9) IS FED THROUGH R412 AND C414 TO AUDIO POWER AMP (IC3).

8
BLOCK DIAGRAM

9
ALIGNMENT INSTRUCTIONS
1. ALIGINMENT LAYOUT
[CPU SECTION ] [ RF SECTION ]
2. TEST EQUIPMENT REQUIRED
1) CPU and Phase Locked Loop Section
¨çFrequency Counter
¨èDC Power Supply
¨éDC Volt Meter
¨êOscilloscope
2) Transmitter Section
¨çRF Power Meter(RF SSVM)
¨è50¥ØLoad(non-inductive)
¨éRF Attenuator
¨êOscilloscope
¨ëAudio Generator
¨ìDC Power Supply
¨íSpectrum Analyzer
¨îFrequency Counter
¨ïModulation Meter
RV803
RV802