KCH-16
19
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
LCD
KEY
H
H
ON
M
M
ON
L
L
ON
OFF
OFF
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).
CONTROL UNIT (X53-4360-20)
Ref. No.
Part name
Description
IC1
IC
Voltage doubling inverter
IC2
IC
LCD contrast
IC3
IC
MIC AMP
IC4
IC
5V AVR
IC5,6
IC
Bus switch
IC8
IC
3.3V AVR
IC9
IC
CPU
Q1
Transistor
9V AVR
Q2,3
Transistor
LCD/12key backlight switch
Q4
FET
LCD/12key backlight switch
Q5
FET
LCD reset switch
Q6
Transistor
LCD backlight switch
Q7,8
Transistor
Hook switch
Q9
FET
DC switch
Q10,11
Transistor
TRD switch
Q12,13
Transistor
PF key backlight switch
Q14
Transistor
BUSY LED switch
Q15
Transistor
TX LED switch
D1
Varistor
Current protection
D2
Zener diode
Voltage reference
D3
Diode
Voltage reference
D6,7
LED
LCD backlight
D8
Varistor
Surge absorption
D9,10
LED
LCD backlight
D11~14
LED
12key backlight
D17~20
Diode
12key control
D21
Diode
DC switch
D24~31
LED
PF key backlight
D32
LED
BUSY LED red
D33
LED
BUSY LED green
D34
LED
TX LED red
D35
LED
TX LED green