Kenwood FM Transceiver TK-481 Service Manual

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

18TK-480/481 CIRCUIT DESCRIPTION6-2. Low battery warningThe battery voltage is monitored by the microprocessor(IC15). When the battery voltage falls below the voltage setby the Low Battery Warning adjustment, the red LEDflashes to notify the operator that it is time to replace thebattery. If the battery voltage falls even more (approx. 5.8V),a beep sounds and transmission is stopped.Low battery warning Battery conditionThe red LED flashes during The battery voltage is low buttransmission the transceiver is still usable.The red LED flashes and The battery voltage is low andcontinuous beep sounds the transceiver is not usable towhile PTT pressed make calls.6-3. Key inputIf the clock is supplied to CLK terminal when the RESterminal (CPU pin 53) of the decade counter (IC301) is set toLow, Q0 to Q7 become High sequentially. Normally, KI1 andKI2 are Low (pulled down). When any key is pressed, KI1 orKI2 become High. The CPU detects which key is pressed,according to the voltage of KI1 and KI2 and clock timing.Fig. 10 Key inputFig. 11 Decade counter timing chart7. Signalling Circuit7-1. Encode• Low-speed data (QT,DQT,LTR)Low-speed data is output from pin 36 of the CPU. Thesignal passes through a low-pass CR filter, and goes to thesumming amplifier (IC3 1/2). The signal is mixed with theaudio signal and goes to the VCO (IC14) and VCXO (X2)modulation input after passing through the D/A converter(IC4) for BAL adjustment.• High-speed data (DTMF)High-speed data is output from pin 35 of the CPU. Thesignal passes through a low-pass filter consisting of IC23,and provides a TX DTMF tone and a RX DTMF tone includinga beep tone. The TX DTMF tone is passed to the D/A con-vertor (IC4) for DTMF deviation adjustment, and then ap-plied to the audio processor (IC12).The signal is mixed with the audio signal and goes to theVCO and VCXO. The RX DTMF tone is passed a summingamplifier (IC3 2/2), the D/A convertor (IC4) for audio control,audio power amplifier and then to the speaker.• MSKMSK signal is output from pin 6 of IC12. The signalpasses through the D/A converter (IC4) for the MSK devia-tion adjustment, and is routed to the VCO. When encodingMSK, the microphone input signal is muted.Fig. 12 EncodeKI2Q5Q1Q0Q2Q6Q7Q3VssVddRESCLKCLCAQ9Q4Q8KRSTCKIC301KI1 IC15CPU16 keysRESETCLOCKQ0Q1Q2Q3Q4Q5Q6Q7Q8Q9CLOCKINHIBITCARRYOUTBUFFAMP VCXOMBX2IC1AFMUTE VCOMDIC14Q21LPF35HSDOUTIC23R111 R107C141C138R148LSDOUTIC15CPUI3I2IC4D/A (ADJ)SUMMIC INSUMIC3 (1/2)O2I1 O1IC12AF AMPSUMO5 I5O336O6I6IC3 (2/2)RX audio