Circuit Description; Components Description - Kenwood KCH-16 Service Manual

CIRCUIT DESCRIPTION / COMPONENTS DESCRIPTION
1. Power supply
Power is supplied to the CPU by converting SB from the
transceiver, via the KRK-11, to 5V by IC4. Additionally, SB is
supplied to the LED for the backlight.
2. CPU
The on/off signals of keys other than the power switch,
and the PTT and HOOK signals, are converted to serial data
and sent to the transceiver via the KRK-11.
Data is displayed on the 14-digit and 3-digit dot matrix
alphanumeric displays.
3. LCD
The LCD is controlled using the bus lines on the connec-
tor (CN1) of the Control unit (X53-436). It corrects the LCD
contrast voltage using VR2.
4. Key detection circuit
Keys are detected using the key scan circuit in IC9. The
KEYI signals that are normally pulled up go low when any
key is pressed.
5. LCD brightness function
From the control of the CPU's DM1/DM2 port, you can
switch the LCD backlight as shown in the following table:
LCD brightness setting
H
M
L
OFF
6. Noise cancelling microphone circuit
The two signals from INT MIC (Main & Sub) are input to
the positive (+) input (Sub) and to the negative (–) input (Main)
of IC3. If the same signal is input to both the Main and Sub,
the Main signal is canceled at the output of IC3 (pin 7). In
other words, if noise from a nearby source, not directly con-
nected to the transceiver, enters the Main and Sub inputs, it
is canceled out.
When a signal is only input to the Main and there is no
signal at the Sub, the Main signal is output as is, from IC3
(pin 7). In other words, only the voice audio of the operator
in close proximity to the Main MIC is input to the Main, and
that voice signal is output from IC3 (pin 7).
LCD KEY
H ON
M ON
L ON
OFF OFF
CONTROL UNIT (X53-4360-20)
Ref. No. Part name
IC1 IC
IC2 IC
IC3 IC
IC4 IC
IC5,6 IC
IC8 IC
IC9 IC
Q1 Transistor
Q2,3 Transistor
Q4 FET
Q5 FET
Q6 Transistor
Q7,8 Transistor
Q9 FET
Q10,11 Transistor
Q12,13 Transistor
Q14 Transistor
Q15 Transistor
D1 Varistor
D2 Zener diode
D3 Diode
D6,7 LED
D8 Varistor
D9,10 LED
D11~14 LED
D17~20 Diode
D21 Diode
D24~31 LED
D32 LED
D33 LED
D34 LED
D35 LED
KCH-16
Description
Voltage doubling inverter
LCD contrast
MIC AMP
5V AVR
Bus switch
3.3V AVR
CPU
9V AVR
LCD/12key backlight switch
LCD/12key backlight switch
LCD reset switch
LCD backlight switch
Hook switch
DC switch
TRD switch
PF key backlight switch
BUSY LED switch
TX LED switch
Current protection
Voltage reference
Voltage reference
LCD backlight
Surge absorption
LCD backlight
12key backlight
12key control
DC switch
PF key backlight
BUSY LED red
BUSY LED green
TX LED red
TX LED green
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