Kenwood TH-K20A Service Manual

TH-K20A/K20E
9
COMPONENTS DESCRIPTION
Ref. No. Use/Function Operation/Condition/Compatibility
IC1 PLL system Frequency control
IC200 FM IF system
2nd mixer, IF amplifi er, FM
detector
IC300 D/A converter
AF mute/MOD level and fre-
quency adjust
IC301 OP AMP
1.8V reference voltage/MIC
amolifi er
IC302 OP AMP Detect AF fi lter
IC303 OP AMP CTCSS/DCS fi lter
IC304 OP AMP MIC amolifi er/IDC
IC305
Voltage
detector/3.3V
MCU reset
IC306
Voltage
regulator/5.0V
5M/5MS power supply
IC307
AF power ampli-
fi e r
Speaker output
IC308
Voltage
regulator/5.0V
5C/5T/5R power supply
IC400 EEPROM Tuning data/Memory data
IC401 MCU
Q1
VCO shift control
switch TX: ON
Q2 Ripple fi lter for VCO power supply
Q3 Oscillator TX/RX VCO
Q4 Buffer amplifi er for VCO output
Q5 RF amplifi er for VCO output
Q6 Logic invert for unlock signal
Q7
Power supply
(3.0V)
for PLL IC
Q101
Pre drive amplifi er
Q102 Drive amplifi er
Q103 Final amplifi er 5.5W RF power
Q104
Voltage dis-
charge switch
for FET bias voltage.
Active ON (VDCSW: H)
Q200
Wide/Narrow
switch
for ceramic fi lter selector
Wide: ON (W/L: L)
Q201 Doubler 2nd Lo: 38.4MHz
Q202 1st IF amplifi er 1st IF: 38.85MHz
Q203 1st mixer
Q204 RF amplifi er RX 1st amplifi re
Q300
Power supply
(5.0V) switch
Active ON (5VC: L)
Q301
SP mute control
switch
Active ON (SM: H)
Q302
SP mute control
switch
for pop-noise Active ON
Q303
Speaker mute
switch
for AF signal line Active ON
Ref. No. Use/Function Operation/Condition/Compatibility
Q304
Power supply
(5MS) switch
Active ON (5MSC: L)
Q305
Speaker mute
switch
for AF signal line Active ON
Q306
IC power supply
switch
for AF power IC Active ON
Q307
Power supply
(5R) switch
Active ON (5RC: L)
Q308
Power supply
(5T) switch
Active ON (5TC: L)
Q400 Beat shift switch Active ON (BSFT: H)
Q401
Backlight LED
switch
Active ON
Q402
Backlight control
switch
Active ON (LAMP: H)
Q403 Busy LED switch Active ON (LEDG: H)
Q404 TX LED switch Active ON (LEDR: H)
D1,D2
VCO frequency
control
D3 RF switch
for frequency range change
TX: ON
D4 VCO modulation for frequency modulation
D5
Assist frequency
control
D6 Speed up for ripple fi lter
D7 RF switch for TX signal TX: ON
D8 RF switch for RX signal
D9, D10 Speed up for ripple fi lter
D11 Speed up for VCO shift control line
D101-104 Antenna switch TX: ON
D200, D201
Band-pass fi lter
tuning
VHF band for receiver
D203
Band-pass fi lter
tuning
VHF band for receiver
D300 VOX signal detect
D301
Reverse connec-
tion protection
Battry terminal
D302
Reverse current
prevention
for IC306 input
D304
Reverse current
prevention
for IC308 input
D401
Over voltage limit-
ter
3.6V zener diode
D404-411
Reverse current
prevention
Key matrix
D414, D415
LCD backlight
LED
D416-425
Key backlight
LED
D426 Busy LED Busy: light
D427 TX LED TX: light
TX-RX unit (X57-821X-XX)

Kenwood TH-K20A Specifications

General

Brand	Kenwood
Model	TH-K20A
Category	Transceiver
Language	English