Service Manual for KENWOOD THF6A

144/220/440MHz FM TRIBANDER / 144/430MHz FM DUAL BANDER

TH-F6A/F7E

B51-8580-00 (S) 798

SERVICE MANUAL

DISASSEMBLY FOR REPAIR .................................................. 2

CIRCUIT DESCRIPTION .......................................................... 4

DESCRIPTION OF COMPONENTS ....................................... 14

PARTS LIST ............................................................................ 19

EXPLODED VIEW .................................................................. 32

PACKING ................................................................................ 33

ADJUSTMENT ........................................................................ 34

PC BOARD VIEWS

TX-RX UNIT (CONTROL SECTION) ...................................... 59

TX-RX UNIT ............................................................................ 65

TX-RX UNIT (VCO SECTION) ................................................ 71

SCHEMATIC DIAGRAM ......................................................... 73

BLOCK DIAGRAM .................................................................. 81

LEVEL DIAGRAM ................................................................... 83

OPTIONS ................................................................................ 85

SPECIFICATIONS .................................................................. 86

CONTENTS

KNOB(ENC)

(K29-5159-03)

WHIP ANTENNA

(T90-0781-05):K

(T90-0789-05):T,E

KNOB(VOL)

(K29-5150-03)

CABINET ASSY

(A02-3620-13):T,E

(A02-3719-13):K

CAP

(B09-0615-23)

FRONT GLASS

(B10-2685-13):T,E

(B10-2723-13):K

KEY TOP

(K29-9107-12)

KNOB(PTT/MONI)

(K29-9108-13)

TH-F6A/F7E

2

DISASSEMBLY FOR REPAIR

1. How to remove the case assembly from

the chassis:

1. Remove 2 screws (1).

2. Remove 2 knobs (2) and 2 round nuts (3).

3. Remove the SP/MIC jack cover (4).

4. Open the bottom part of case assembly and lift the front

panel from the chassis (5).

2. How to remove the main PCB:

2-1. Control section

1. Remove the SP/MIC jack cover (6).

2. Remove 5 screws (7) and lift and remove the control PCB

(TX-RX A/3).

3. Extract the encoder flat cable from the connector.

2-2. RF section

4. Remove 8 screws (8), and 1 round screw (9), then remove

the RF shield cover. Remove the soldering that connects

the whip antenna and bar-antenna (3 locations).

5. Remove the battery terminal screw (0).

6. Lift and remove the RF PCB (TX-RX B/3).

2-3. PLL/VCO section

7. Remove the soldering (8 locations) that holds the PLL/VCO

shield cover (!) then lift the shield cover.

8. Lift the PLL/VCO PCB upward to seperate it from the main

PCB.

3

1

2

4

6

7

8

9

10

5

11

Fig. 1

TH-F6A/F7E

3

DISASSEMBLY FOR REPAIR

3. Soldering the Bar antenna wires

Before solding the bar antenna wires, form the wires as

shown in the figure 2.

Then solder the wires to lands on the PCB.

Fig. 2

4. Removing a relay terminal

Insert a screw driver between the relay terminal and its

holder.

Then pull the relay terminal as shown in the figure 3.

5. Assembling a release latch

Place a coil spring(1) on the release latch(2) as shown in

the figure 4.

Then insert a shaft(3) into the release latch.

Push the above assembly into the rear panel while the

end of coil spring is hooked to the "A" tab.

Fig. 4

2

1

3

Notch

A

6. Caution at the time of reassembling

While you are reassembling the battery terminal holder

(J19-5428) and the packing (G53-1532), confirm that the

packing is reassembled at the condition that any swell is

not occurred on it. If the packing is assembled with any

swell, width of body also becomes expansive.

J19-5428

G53-1532

Swell not

allowed

Fig. 3

Fig. 5

TH-F6A/F7E

4

CIRCUIT DESCRIPTION

1. A band receiver system

1-1. Receiver circuit

The A band can receive signals in two bands: VHF (220 MHz

band <K type only>) and UHF (K type: three bands). It uses

FM receive mode only, and uses double conversion with the

first IF of 59.85 MHz and the second IF of 450 kHz.

The first amplifier is divided into two bands: 137 MHz -

173.995 MHz (216 MHz - 260 MHz <K type only>) and 410 MHz

- 470 MHz. The incoming signal from the antenna passes

through a low-pass filter and a duplexer, and goes to an

independent amplifier (Q63, Q62) for each band.

1-1-1. VHF band frontend

The incoming signal from the antenna passes through a

VHF band low-pass filter and a duplexer, passes through a

band-pass filter where it is tuned with varicaps (D76, D77),

and goes to the first amplifier (Q63). Unwanted signal

components are eliminated by a two-pole band-pass filter

where it is tuned by varicaps (D72, D75, D81, D83), and the

signal goes to the common mixer (Q45) for the A band. (K

type only: For 200MHz band reception, D74 is turned off with

a control signal to improve band-pass filter coupling and

ensure pass bandwidth.)

ANT

Q45

MT6C

04AE

BPF

APC&VTUNEA

MIX

Q63

3SK320

RFAMP

BPF

MPU

D76

D77

D72,D75

D81,D83

LPF

LO

1st IF

59.85MHz

Fig.1

1-1-2. UHF band frontend

The incoming signal from the antenna passes through a

UHF band low-pass filter and enters the first amplifier (Q62)

common to both A and B bands. The amplified signal is

distributed by L distributors (L95, L96) and goes to the LC filter

module (L92). Unwanted signal components are eliminated

by the filter, and the resulting signal passes through another

band-pass filter and enters the mixer (Q45).

ANT

BPF

Q62

3SK320

RFAMP

L95

L96

HPF

LPF

L92

Q45

MT6C

04AE

MIX

LO

1st IF

59.85MHz

BPF

LC FILTER

MODULE

1-1-3. Circuits following IF

The signal heterodowned to the first IF of 59.85 MHz by the

mixer (Q45) passes through a 15kHz MCF (XF2) and unwanted

signal components are eliminated. The resulting signal is

amplified by the IF amplifier (Q43) and goes to the FM IC (IC7).

The FM IC heterodowns it to the second IF of 450 kHz. Then,

the signal passes through a 15kHz external ceramic filter (CF4)

and goes to the FM IC again. The signal amplified by the IF

amplifier built into the IC is demodulated by the quadrature

FM demodulation circuit using a discriminator (CD1) and

converted into an audio signal and output.

The FM modulation signal output from the FM IC passes

through a low-pass filter consisting of a resistor and a capacitor

and is output to the control section. The demodulation signal

input to the control section goes to the electronic volume

(IC706, pin 13) to adjust the audio balance with the B band.

The output signal is amplified by the operational amplifier

(IC717), passes through an active filter consisting of Q719 and

Q717, and goes to the audio amplifier (IC707). The signal

amplified to a higher power by the audio amplifier becomes

the final output signal from the set and output through the

internal speaker or speaker output pin (J701).

Q45

MT6C

04AE

MIX

LO

X3

IC7

XF2

X1

TCXO

Q44

2SC

4915

IFAMP

MCF

Q43

2SC

5108(Y)

19.8MHZ

CF4

4.50KHz

LPF

IC700

VR

BAF

IC707

Q719

Q717

AUDIO

AMP

DE EMPHASIS

IC717

AMP

SP

J701

Fig.3

Fig.2

1-2. Mixer local oscillator

1-2-1. First mixer

The local oscillator signal for the first mixer is supplied from

the VCO-PLL circuit.

1-2-2. Second mixer

The local oscillator signal for the second mixer is a 59.4

MHz signal that is produced by multiplying the 19.8MHz TCXO

(X1) oscillator output with a multiplier (Q44).

2. B band receiver system

2-1. Receiver circuit

The B band has a broadband receiver circuit configuration

and implements broadband reception of 100 kHz to 1.3 GHz.

FM/AM/SSB/CW reception is possible in the range 100 kHz to

29.7 MHz, and FM/wide FM/AM/SSB/CW reception is possible

in the range 29.7 MHz to 1.3 GHz. The FM/AM receiver circuit

uses double conversion with the first IF of 57.6 MHz and the

second IF of 450 kHz. The SSB/CW receiver circuit uses triple

conversion with the first IF of 57.6 MHz and the second IF of

450 kHz. The wide FM receiver circuit uses single conversion

with the IF of 10.8 MHz.

TH-F6A/F7E

5

CIRCUIT DESCRIPTION

Fig.4

The first amplifier is divided into four bands: 100 kHz - 50

MHz, 50MHz - 108MHz, 108 MHz - 265 MHz, 265 MHz - 600

MHz, and 600 MHz - 1.3 GHz. The incoming signal from the

antenna passes through a low-pass filter and a duplexer, and

goes to an independent amplifier for each band. Then, the

signal goes to the second common broadband amplifier (IC10)

and its output is fed to the mixer (Q28) and heterodowned to

the first IF.

2-1-1. FM/AM receiver circuit

The signal heterodowned to the first IF of 57.6MHz passes

through a 15kHz MCF (XF1), and unwanted signal components

are eliminated. The resulting signal is amplified by the IF

amplifier (Q26) and goes to the FM IC (IC5). The FM IC

heterodowns it to the second IF of 450 kHz. In FM mode, the

signal passes through a 12.0kHz external ceramic filter (CF3)

and goes to the FM IC. The signal amplified by the internal IF

amplifier is demodulated by the quadrature FM demodulation

circuit using a coil (L19) and converted into an audio signal

and output. In AM mode, the signal passes through a 4kHz

external ceramic filter CF1 and goes back to the FM IC. It is

amplified by the AM AGC amplifier built in the FM IC, an audio

output from the FM IC as an audio signal.

2-1-4. AM bar antenna receiver circuit

This unit incorporates an AM bar antenna, and either the

bar antenna or the supplied antenna can be selected in the

520kHz-1.8MHz (SW) and 3.5MHz-10.1MHz (MW) bands (the

initial value: bar antenna). The bar antenna has two kinds of

tuners for SW and MW tuning, one of which is selected with a

switching FET (Q32, Q48, Q52). The antenna is tuned with a

varicap (D60) for AM tuning to select a desired signal. The

signal from the bar antenna is amplified by and its impedance

is converted by the buffer amplifier (Q59), and the resulting

signal goes to the common mixer (Q28) for the B band. The

signal is routed over the same path for AM demodulation as

for the supplied antenna after leaving the mixer.

19.05MHZ

FINE2

D20,24

KV1566J

TUNE

IC4

TA4101F

SSB DET

SSB/CW

Q22,29

UPA672T

IC5

TK10931V

SW

FM

AM

SMB

SQB

Q23

LMX

2N

OSCILLATOR

453KHz

SW

CF1

450KHz

CF3

CF2

10.8MHz

D25

DAN

235E

TUNE

D29

HVC

376B

Q27

2SC

4915

OSCILLATOR

Q26

2SC

4915

IF AMP

Q28

MT6C

03AE

MIX

FINE1

UHF(600~1300)

UHF(265~600)

VHF(108~265)

HF

IC10

MPC2746TB

AMP

LO

57.6MHz

XF1

10.8MHz

MCF

Q24

2SC

4915

CF5

Q28

MT6C

03AE

SW

IC10

MPC2746TB

AMP

D57

HSC277

TUNE

D60

KV1566J

SW

BAR

ANT

Q6,Q4

Q48,52

2SK1824

Q32

2SK1830

MIX

LO

Q59

3SK320

RF AMP

Fig.5

2-1-5. Audio signal

The FM and AM demodulation signals output from the FM

IC (IC5) pass through a low-pass filter consisting of a resistor

and a capacitor, and goes to the switching FET (Q29), from

which a switched signal is output to the control unit. The

SSB/CW demodulation signal passes through an RC LPF,

connects to the Q29 output section, and output to the control

unit through a line common to all modes. The demodulation

signal input to the control unit goes to the electronic volume

(IC706, pin 16), the audio balance output with the A band is

restricted, then the signal is output. It joins the A band

demodulation signal and is processed in the same manner

for both A and B bands.

signal demodulated by the diode detection circuit is output.

2-1-2. SSB/CW receiver circuit

In SSB/CW mode reception, the signal takes the same path

to CF1 as in AM mode. The signal input to the FM IC again is

amplified by the AM AGC amplifier in the FM IC, then output

from the AM IF output pin. The signal is fed to the third mixer

(IC4) and converted to an audio signal and output.

2-1-3. Wide FM receiver circuit

The signal converted to the first IF of 10.8 MHz passes

through a ceramic filter CF5 for wide FM, and is amplified by

the IF amplifier (Q24). The signal passes through ceramic filter

CF2 again to eliminate unwanted signal components, and goes

to the FM IF input (pin 7) of the FM IC. The input signal is

amplified by the IF amplifier in the IC, demodulated by the

quadrature FM demodulation circuit using an L18 coil, and

KENWOOD THF6A Service Manual

Manual details

We guarantee that...

Sample pages

Reviews

Related Products

KENWOOD KSW-7000 Service Manual

KENWOOD TS-950S/SD Owner's Manual

KENWOOD R-SG7 Owner's Manual

KENWOOD KX-550HX Service Manual

KENWOOD X-MB3 Owner's Manual

Popular Brands

General

Members Area