Kenwood TM-631A Service Manual page 11

T
M-631A
CIRCUIT DESCRIPTION
The unlock circuit operates
only
in
the transmitter circuit.
A
description
of
the
430
MHz unlock circuit follows. Q10
is
the
PLL unlock switching transistor. Normally the base of Q10
is
Low (0 V)
and the
collector
of
Q10
is
High (8
V).
When
the
PLL unlocks
0.7 V
dc
is
applied to the base of
Q10,
Turning Q10
on
forcing
the
collector
to
0 V (Low). This swit-
ches Q8 off. When
the
PLL unlocks
(during transmission), the
collector
of Q8
goes
to 8
V
(instead
of the normal 0 V} and
Q11 turns off. Therefore the
8T
switching
transistor Q11 turns
off and the transmit bias voltage goes dead. This prevents trans-
mitter output
when
the
PLL
is
unlocked.
e
8R (Receive
8 V) Stop Circuit
In receiving,
the base of
Q13 receives
an 5
V
dcsignal that turns
Q13
on
(so the collector of
013
goes
to 0
V). Q12
then turns
on and provides
8
X
at its
collector.
(In
receiving, 8
V
is
sup-
plied from
8C (Common
+8
V)
to
8R.)
-During transmit, serial data from the microprocessor
is pass-
10
ed thru shift register IC4. The output from IC4
at pin
11
goes
Low. 01
3 therefore turns off (its collector voltage going to 8
V)},
Q12 turns
off, and no
8R output
is
provided from the collector
of
O12.
The PLL
IC
(M54959FP) can
be
controlled
for its
two refer-
ence division
ratios and single comparison division ratio.
The pulse-swallow PLL circuit
is
contained on
a
single chip and
consists
of
a
built-in
dual-modulus (1/128
and
1/129)
prescaler.
The switch function
(pin
10)
of the PLL
IC
controls the 8T1
(TX
+8
V (430 MHz))
and
8T2 (TX
+8
V (144 MHz))
lines.
Bc
012
Shift
register,
IC4
pin
11
ec
Fig. 13 8R Stop Circuit
®
8T2
(Transmit
8V)
and
Unlock Circuit
Dueing receive,
0.7 V
desional
is
applied
to the base of Q9
which turns Q9 on,
Q8 off, and Q11 off, so
no
voltage
is
out-
put at the
collector (8T2) (TX
+8
V) of
Q11.
When
the
PTT
(Push-to Talk) switch
is
depressed,
serial data
is
sent from the
microprocessor
to
IC1
(the
phase-locked oop)
causing
pin
10 of
IC1
to
go Low. This switches Q9 off, Q8
on, and Q11 on, so that
8
V
is
applied
to
8T2.
(In
transmis-
sion,
8
V
is
applied
to
8T2
from
8C.)
Ov
(8.0V)
(OV)
Git
:2SBIII9S
8T2
Subunit,
IC1 pin
10
(TR2)
8.0V
(ov)
%(8.0V)
ec
ox ac
«2
0.7V
wx
(Ov)
22K
013
8
+
os /
a9g
On
R68
Ov
22K
014
8.0V)
%
(OV)
NX
on
Subunit,
ov
IC1 pin
14 (TR2)
(Ov)
¥(0.7V)
* When unlocked
Fig. 14
8T2 (Transmit 8 V)
and
Transmit Unlock Circuits
5V
(Ov)
(OV)
#7
ERG
ST2
R70
(8V)
47K
+
(1/128
and