Kenwood TK-3312 Service Manual page 15

Q8
TX VCO BUFF
(TX: High)
CV
Q2
RF
LPF
AMP
IC1
21 17
PLL
7 10
PL_UL
MCU
PL_STB,PL_CLK,PL_DAT
IC820
Fig. 6 PLL block diagram
5. Control Circuit
The control consists of the MCU (IC820) and its peripher-
al circuits. It controls the TX-RX unit. IC820 mainly performs
the following;
1) Switching between transmission and reception by PTT
signal input.
2) Reading channel information, frequency, and program
data from the memory circuit.
3) Sending frequency program data to the PLL.
4) Controlling squelch on/off via the DC voltage from the
squelch circuit.
5) Controlling the audio mute circuit via the decode data in-
put.
6) Transmitting tone and encode data.
5-1. Frequency Shift Circuit
The MCU (IC820) and baseband IC (IC812) operates at
a clock frequency of 19.2MHz. The oscillator circuit has the
baseband IC. This oscillator has a circuit that shifts the fre-
quency via Beat shift switch (Q807).
A beat sound may be able to be evaded if "Beat Shift" is
set to ON when it is generated in the internal spurious trans-
mission modulated sound of the transceiver.
Baseband IC
XOUT
39
C854
H: OFF
L: ON
MCU
BSHIFT
Q807
Fig. 7 Frequency shift circuit
CIRCUIT DESCRIPTION
Q9 D18
BUFF SW To
RF AMP
D17
SW
To mixer
VC
Baseband
TCXO
IC
X1 IC812
IC812
XIN
40
X802
R857
MCU
XIN
TK-3312/3317
5-2. Memory Circuit
The Memory circuit consists of the MCU (IC820) and
EEPROM (IC810). The EEPROM has a capacity of 512k bits
and stores the channel information, the last channel data,
the scan on status, and other parameters.
■ EEPROM
Note:
The EEPROM stores tuning data (Deviation, Squelch,
etc.).
Realign the transceiver after replacing the EEPROM.
IC820
MCU
Fig. 8 Memory circuit
5-3. Low Battery Warning
The battery voltage is monitored by the MCU (IC820 pin
63: BATT). When the battery voltage falls below the voltage
set by the Low Battery Warning adjustment, the red LED
blinks, notifying the operator that it is time to replace the bat-
tery (when the always option (default setting) under the Bat-
tery Warning function in the FPU is selected). If the battery
voltage falls bellow 5.9V, the transceiver does not transmit
and the warning tone beeps while the PTT switch is pressed.
Low battery warning
The red LED blinks during
transmission.
The red LED blinks and the
warning tone beeps while the
PTT switch is pressed.
R824
SB
Fig. 9 Low battery warning
IC810
EEPROM
Battery status
The battery voltage is low but
the transceiver is still usable.
The battery voltage is lowand
the transceiver cannotbe used
to make calls.
63
BATT
IC820
MCU
15