Kenwood TM-V708A Service Manual page 13

7-2. Reception signals
PR9 is the 9600bps data communications reception
output. It outputs the FM detection circuit output (RD signals)
through a buffer amp (Q700). These signals are always
output whether the squelch is open or closed.
PR1 is the 1200bps data communications reception
output. It outputs the FM detection circuit output (RA signals)
through a buffer amp (Q701). Output is controlled with the
cross point switch (IC702) according to whether squelch is
open or closed.
7-3. Squelch signal output circuit
The squelch circuits is input to the TNC to prevents
conflicts from occurring between simultaneous receive
m o d e a n d t r a n s m i t m o d e t r a f f i c d u r i n g p a c k e t
communications. (only during 1200bps) The signal is output
from Pin 15 of IC703 to the data terminal. The logic is as
shown in the Table below.
SQC terminal output
(J700 Pin 6)
8. Panel Section (LCD ASSY: B38-0829-05)
The panel section controls serial communications with the
main unit control section, the key input circuit, the display
circuit, and the dimmer circuit through the microprocessor
(IC4).
8-1. Serial communications circuit
A buffer amp is inserted in order to protect the
microprocessor ports.
8-2. Key, Volume Input circuit
Circuits to operate the panel section keys are connected
to each microprocessor port. The PSW key is pulled up and
the other keys are pulled up with software within the
microprocessor. Rotary encoder operating circuits are
connected directly to the microprocessor. The control divides
the power supply voltage, reads the A/D port of the
microprocessor, and transfers that data to the main unit.
CIRCUIT DESCRIPTION
L: SQ CLOSE
H: SQ BUSY
8-3. Display circuit
The TM- V708A display section is a 188x54-dot full-dot
matrix LCD controlled by two LCD. As shown is Figure 17,
the master IC (IC2) side is connected to 22 common dots and
88 segment dots and the stave IC (IC1) side is connected to
33 common dots and 100 segment dots. The LCD drive
voltage is obtained by raising the power supply voltage (5V)
within the IC.
22
LCD
COM
188 × 54 (dot)
88
SEG
LCD
Driver
IC2
Microprocessor
Fig. 17 Display circuit
8-4. Dimmer circuit
The dimmer circuit switches the lamp brightness to one of
four levels or OFF. (See table7) The current flowing to the
LEDs is varied by selecting resistors from R8 to R14.
Dimmer level DIM 0
1 H
2 L
3 L
4 L
OFF L
Table7 Port logic
IC4
Microprocessor
R13
DIM3 Q8
R14
R11
DIM2 Q7
R12
Q6
DIM1
Q5
Q4
R10
Q3
R8
DIM0
Q2
Fig. 18 Dimmer circuit
TM-V708A
33
COM
100
SEG
LCD
Driver
IC1
IC4
X54-329
DIM 1 DIM 2 DIM 3
L L L
H L L
L H L
L L H
L L L
9V
LCD ASSY
R9
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