Kenwood FM Transceiver TK-481 Service Manual

Also see for FM Transceiver TK-481: User manual Instruction manual Specifications Instruction manual Service manual

19TK-480/481CIRCUIT DESCRIPTION7-2. Decode• Low-speed data (QT,DQT,LTR)The demodulated signal from the IF IC (IC9) is amplifiedby IC8 (1/2) and passes through a low-pass filter (IC10) toremove audio components. The signal is input to pin 23 ofthe CPU.The CPU digitizes this signal, performs processing suchas DC restoration, and decodes the signal.• High-speed data (DTMF)The DTMF input signal from the IF IC is amplified by IC8(1/2) and goes to IC13, the DTMF decoder. The decoded in-formation is then processed by the CPU. During transmis-sion and standby, the DTMF IC is set to the power downmode when the PD terminal is High. When the line is busy,the PD terminal becomes Low, the power down mode iscanceled and decoding is carried out.• MSKThe MSK input signal from the IF IC is amplified by IC8 (1/2) and goes to pin 5 of IC12. The signal is demodulated byMSK demodulator in IC12. The demodulated data goes tothe CPU for processing.Fig. 13 Decode8. Power Supply CircuitBattery +B is supplied via a 3A fuse from the battery ter-minal connected to the TX-RX unit. After passing throughthe power switch, power supply (SB) is applied to the threeAVRs. IC5 supplies 5V (5M) to the control circuit, and IC7supplies 5V (5C) to common circuits. IC6 supplies to the TXcircuit and the RX circuit. During transmission, 5TC be-comes Low and Q2 is turned ON to supply 5V (5T) to the TXcircuit. During reception, 5RC becomes Low and Q1 isturned ON to supply 5V (5R) to the RX circuit.Fig. 14 Power supply circuit9. Optional Board TerminalTerminals for mounting the option board are provided atthe bottom edge of the TX-RX unit. The table below showsthe correspondence between the board and terminals.R422, R32, R250, R259, R147, R276, R421 may have to beremoved depending on the type of option board being used.Name FunctionSB Battery (7.5V)GND GroundTXD Serial dataRXD Serial dataSQ Busy: highLOK Link acquired : low (TX mode)DI/ANI Modulation (ANI) inputDEO Detect outputTXAI/MUTE Modulation output from board or mic mute: lowTXAO Modulation input to boardRXAI Received signal input to boardRXAO Received signal output from boardD1 Binary 1D2 Binary 2OPT Scramble, Emergency: lowPTTIN PTT switch signal input to board (TX: low)5CNS Battery (5V)DI9 9600 bps data outputRXEMAO Received signal output from board (after de-emphasis)RXEMAI Received signal input to board (after de-emphasis)PTTOUT PTT switch signal output from board (TX: low)MONI Busy: lowLAMP Busy: lowAAC Audio Amp Control signal output from board (Busy: high)Audio Beep Beep signal output from boardAUX TXD Serial dataAUX RXD/EXTSW Serial data/Option switch portTable 1 Terminal name and functionIC10LPFIC13DTMFDECODEIC12XOUT OSC1PDDCK,SD,STDDT,CK,CE7 IC1923 LSDINIC15CPUIC8AMPIC5SBIC7IC65TCQ25T5RC5R5M5C+BF1ON/OFFVOLRF power amp (IC30)Display unitQ1