Kenwood TM 742 E Service Manual

Page 2

TM-742 A/ 742 E/942 A
OVERVIEW "2

List of Destinations ,, :

Model Destination Destination code Model Destination Destination code

TM-742A North America K TM-942A North America K

TM-742A Canada P TM»942A Canada P

TM-742E Europe E TM-942A Other countries M

TM-74ZE Europe E2

TM-742E Europe E3

TM-742A Other countries M

TM-742A Other countries M2

Units for Each Model and Destination

Band Units
n" "am 9" "°- TM'nZAIE TM 942A UT-zas UT-sos UT-zzos UT-1200
K P E 52 E3 M M2 K P M M [50) M (50) K (50) M (10)

Control Unit X53-3460v11 o o 0
Control Unit XSS-SAGO-Zl o 0
Control Unit X53-3460-22 0
Control Unit X53646271 o 0
Control Unit X53-3462-72

Display Unit X54-3130-11 o o o o o o o o o o

ZBTX-HX X57-3790v0l o

50TX-RX X57-3800v01 o

lMTX-RX X57-3580~1 l o o o __
144TX-RX X57-3580~12 O o o o o o o

ZZOTX-RX X57-3810-10 o

MOTX»RX X57-3590-12 o o o

430TX-RX X57-359022 o o

430TX-RX X57~3592-72 O o o o

1200TX»RX X57-3600-1 1 o o o o

7
BAND UNITS

Any of the following optional band units may be installed
in the TM-742A/742EA
The same instructions apply for the Tri-Bander as for the

Dual-bender.
OPTIONAL BAND UNIT
TM-742A
UrS.A. Version UT»285 UT-SOS UT-ZZOS UT1200

TM»742A UT-ZBS UT-SOS UT-1200
TM-742E UT-ZBS UT-SOS UT~12OO

Page 19

TM-742A/742 E/942A
CIRCUIT DESCRIPTION

12

144 TX-RX Unit Transmit Signal Channel

0 Outline

In the transmission channel, the desired frequency is
directly oscillated and directly frequency modulated by
means of a varicap diode.

0 Modulator circuit

The audio signal from the control unit is input to
microphone amplifier HlC |C7 (KCAO4). 1C4 consists of
a preemphasis circuit, amplifier, limiter, and splatter
circuit that eliminate unwanted high-frequency
components. The voltage-controlled oscillator (VCO)
signal is directly frequency modulated by means of a
varicap diode in the frequency modulator circuit.

I Younger-stage circuit

The signal output from the VCO is input to drive
circuit H IC ICB (KCB1 1). The amplifiercan obtain a stable
drive output without adjustment because it has a wide
band. An APC circuit controls the collectorvoltage in the
younger final stage.

144 TX-RX Unit PLL Synthesizer

The VCO and PLL circuit are housed in a solid
shielding case as a hybrid integrated circuit. Com-
parison frequencies of 6.25 kHz and 5 kHz are produced
by dividing a 12.8 MHz reference oscillation frequency
by 2048 and 2560 to correspond to 5, 10, 12.5, 15, 20,
and 25 kHz channel steps.

For 144 MHz, the relationship between fvwmx)

and each frequency division ratio is given by

fvco=l144- 10.7): {(n x 128) + A) x toSC + Fl

Where: fvco= VCO output frequency

n 2 Binary 10-bit programmable counter setting value

A: Binary 7-bit programmable counter setting value

fox: Reference oscillation frequency of 12.8 MHz

0V _ 5V_ :3 HD «- Moduiation
during lock _ NC 10C --lOV input
Xl 8CL ~8V
. H NC -
12 B M z 1: X0

CV -> Lock voltage
E r-E
HT -» HET output

Data input - DP
Clock input -> CP
Enable input -> EP

Fig. 12 IC11 KCH05

- Power amplifier circuit
A drive signal is input to power module |C10 and
amplified to the specified level.

0 APC circuit

The automatic transmission output control circuit
(APC) detects and partially amplifies the power module
output with a diode and controls the output control
voltage. The control voltage is output in inverse proportion
to the output, so the control voltage output is always
constant. To protect the set against excessive
temperature rise, the high-power unit has a thermal
switch. The high-power unit is automatically set to a low
power by the thermal switch when it exceeds the
specified temperature.

R: Binary 14rbit programmable counter setting value
2048
In this case, n is 208, and A is 36.
Therefore, fvco= ((208 x 128) + 36) x 12800 / 2560
= (26624 + 37) x 5
= 133300 kHz = 133.300 MHz
The following table lists the pin functions of the PLL
circuit:

Pin Pin

name Function name Function
Modulation signal
5C 5V M0 input
LD Lock signal (on during 10C 10V
lock)
NC Unused ECL 8V (ripple filter)
XI 12.8 MHz crystal NC Unused
x0 °5C'"a"° cv Lock voltage output
DP Data input E GND
CP Clock input HT HET output

EP Enable input

Table 12