Kenwood TM-321A Service Manual page 13

321A
14
DESCRIPTION OF ELEMENTS
Element Function
Description
Q21
High-pass
filter
Improves
AF
frequency characteristics
in
the receive mode.
D1
Limiting
Limits the first IF
signal.
D2 Reversal current protection
Turns
on the
SQ circuit
and
04
for
AL,
in
transmit mode for muting of the
AF
line
D3 Reversal current
protection
Prevents
flow of
RF
meter current
to the microphone check circuit
and rectifies the
microphone check output.
D4
Discharge
For discharging
any residual charge
on
the
8T
line.
DS
AVR
Zener diode for setting the
AVR
circuit reference voltage.
D6
Switching characteristic Diode to provide
rise and
fall hysteresis
on
the
LD
line.
D7
VCO
output switch
Reduces the drive circuit
load
in
receive mode.
D8
VCO
output switch Reduces the oscillator load
in
transmit mode.
D9
Temperature compensation
Temperature compensation for Q19 (driver).
D10
Temperature compensation
Temperature compensation for
APC
circuit.
D14
Protect for S-meter circuit when
TX
to
RX
mode.
S-meter circuit protection
VCO
(X58-3090-11)
Element Function
Description
Qi
Amplifier
Operates
in
all modes to amplify
the
VCO
output to the
required level
Q2 Transmit
VCO
Operates in
transmit mode as the
PLL VCO
(220MHz
band).
Q3 Transmit
VCO
switch Turns
on
the transmit VCO.
Q4
Receive
VCO
Operates in
receive mode
as
the
PLL VCO.
01
OR circuit
ORs
8T
and
8R
to operate
Q1
at normal temperature.
D2 Transmit modulation varactor Adds FM modulation to
TX
VCO.
D3 Transmit frequency control varactor
D4
Receive frequency control varactor
DRIVE
(X59-3120-11)
Element Function
Description
Qi
Switching Supplies
8V
to the drive circuit; switched by Q3.
Q2
Switching Supplies
8V
to the
local
oscillator amplifier; switched by Q3.
Q3
Switching
ON when the
PLL
is
locked.
Operates in
transmit
mode. When
checking
levels near these transistors,
be
careful
Q4,05
High-frequency amplifier
of
the probe ground points.
D1
Reversal current
protection Separates Q1
and O2.
APC (X59-3130-00)
Element Function
Description
Qi
Differential amplifier
Q2(1/2) Protection control Adjustable with
VR5.
Q2(2/2)
APC
control Adjustable with
VR6.
Q3 Drive
stage
+
B
AVR
IF (X59-3140-00)
Element
Function
Description
Second local oscillator, mixer, IF ampli-
@
S-meter output.
Noise amplifier
output (first stage).
IC1
fier, quadrature detector, noise
amplifier
@
Detector output
@
First tF
signal input.
321A
14
DESCRIPTION OF ELEMENTS
Element Function
Description
Q21
High-pass
filter
Improves
AF
frequency characteristics
in
the receive mode.
D1
Limiting
Limits the first IF
signal.
D2 Reversal current protection
Turns
on the
SQ circuit
and
04
for
AL,
in
transmit mode for muting of the
AF
line
D3 Reversal current
protection
Prevents
flow of
RF
meter current
to the microphone check circuit
and rectifies the
microphone check output.
D4
Discharge
For discharging
any residual charge
on
the
8T
line.
DS
AVR
Zener diode for setting the
AVR
circuit reference voltage.
D6
Switching characteristic Diode to provide
rise and
fall hysteresis
on
the
LD
line.
D7
VCO
output switch
Reduces the drive circuit
load
in
receive mode.
D8
VCO
output switch Reduces the oscillator load
in
transmit mode.
D9
Temperature compensation
Temperature compensation for Q19 (driver).
D10
Temperature compensation
Temperature compensation for
APC
circuit.
D14
Protect for S-meter circuit when
TX
to
RX
mode.
S-meter circuit protection
VCO
(X58-3090-11)
Element Function
Description
Qi
Amplifier
Operates
in
all modes to amplify
the
VCO
output to the
required level
Q2 Transmit
VCO
Operates in
transmit mode as the
PLL VCO
(220MHz
band).
Q3 Transmit
VCO
switch Turns
on
the transmit VCO.
Q4
Receive
VCO
Operates in
receive mode
as
the
PLL VCO.
01
OR circuit
ORs
8T
and
8R
to operate
Q1
at normal temperature.
D2 Transmit modulation varactor Adds FM modulation to
TX
VCO.
D3 Transmit frequency control varactor
D4
Receive frequency control varactor
DRIVE
(X59-3120-11)
Element Function
Description
Qi
Switching Supplies
8V
to the drive circuit; switched by Q3.
Q2
Switching Supplies
8V
to the
local
oscillator amplifier; switched by Q3.
Q3
Switching
ON when the
PLL
is
locked.
Operates in
transmit
mode. When
checking
levels near these transistors,
be
careful
Q4,05
High-frequency amplifier
of
the probe ground points.
D1
Reversal current
protection Separates Q1
and O2.
APC (X59-3130-00)
Element Function
Description
Qi
Differential amplifier
Q2(1/2) Protection control Adjustable with
VR5.
Q2(2/2)
APC
control Adjustable with
VR6.
Q3 Drive
stage
+
B
AVR
IF (X59-3140-00)
Element
Function
Description
Second local oscillator, mixer, IF ampli-
@
S-meter output.
Noise amplifier
output (first stage).
IC1
fier, quadrature detector, noise
amplifier
@
Detector output
@
First tF
signal input.