Kenwood TK-3401D Service Manual page 9

2.3.5 Control Circuit
The control consists of the MCU (IC710) and its peripheral circuits. It controls the TX-RX unit. IC710 mainly performs the following;
(1) Switching between transmission and reception via the 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 input.
(6) Transmitting tone and encode data.
2.3.5.1 Memory Circuit
The Memory circuit consists of the MCU (IC710) and EEPROM (IC700). The EEPROM has a capacity of 64K-bit and stores the chan-
nel 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.
2.3.5.2 Low Battery Warning
The battery voltage is monitored by the MCU (IC710 pin 33: BATT). When the battery voltage falls below 6.0V approximately, the red
LED blinks, notifying the operator that it is time to replace the battery (When "Always-Late Warning" option (default setting) under the
Battery Warning function in the FPU is selected).
If the battery voltage falls below 5.5V approximately, the transceiver does not transmit and a warning tone beeps when the PTT switch
is pressed (When the Battery Warning Tone is selected in the FPU).
2.3.5.3 Key Input
Keys and channel selector circuit.
The signal from the keys and channel selector are directly input to the MCU, as shown in Figure 7.
2.3.6 Signaling Circuit
2.3.6.1 Encode
Low-speed data (QT, DQT)
Low-speed data is output from pin 29 of the MCU. The signal passes through the low pass CR filter, and goes to the audio processor
(IC705). The signal is mixed with the audio signal and goes to the VCO and TCXO (X1) modulation input after passing through the
D/A converter inside the audio processor (IC705) for BAL adjustment.
2.3.6.2 Decode
QT/DQT
The output signal from the FM IC (IC400) enters the MCU (IC710) through IC705. IC710 determines whether or not the QT or DQT
matches the preset value, and controls the AFSW and speaker output sounds according to the squelch results.
Selector
IC710
MCU
66
EN4 PTT
64
EN3
Side1
65
EN2
63
EN1 Side2
Fig.7 Key input
PTT
SW
Side1
59
60
Side2
61
(No.RA012<Rev.001>)1-9