Kenwood TK-380 Service Manual

Also see for TK-380: User manual Instruction manual Instruction manual Pricing and specification manual Service manual

Contents

TK-38017CIRCUIT DESCRIPTIONFig. 3 Wide/Narrow changeover circuit5RQ6Q7 D5R39R42C51C9R47D7R56W/N "H" : Wide"L" : NarrowMXOIFIMXIAFODMC100R117R71C77IC12FM IF SYSTEMQ12C61R46C49 CF1CF2R43Q15 C119Q9C92R74W/NFig. 4 Audio amplifier circuit3-4. Audio amplifier circuitThe demodulated signal from IC12 goes through the muteswitch (Q15) and is amplified by IC4 (2/2), high-pass filtered,low-pass filtered, high-pass filtered, band-eliminate filtered, andde-emphasized by IC13.The signal then goes through an AF amplifier IC7 (2/2), anelectronic volume control (IC8), and an AF switch (Q310 ison), and is routed to audio power amplifier (IC300), where it isamplified and output to the internal speaker.The audio mute signal (AM) from the shift register becomesLow in the standby and Q304, Q305 which are power supplycircuit for IC300 turn off. Also, IC13 is set to the power downmode according to data from microprocessor, and the AF signalis muted. When the audio is output, AM becomes High to turnQ304, Q305 ON, and voltage is supplied to power terminal VPof IC300. Also, IC13 is canceled out of the power down mode.The speaker is switched by the logic of speaker switchingterminal SSW on the universal connector. When SP-MIC isnot attached, the logic of SSW becomes High and SW (Q310)is turned ON, and the AF signal is input to both amplifiers ofIC300.When SP-MIC is attached, SSW is connected to GND atinside of SP-MIC. For this reason, Q310 is turned OFF, andthe AF signal is input only to amplifier for EXT SP of IC300.Change of INT/EXT SP refer to Fig. 4.AM SSW VC1 VC2 SPH H H L INTH L L H EXTL H L L MUTEL L L L MUTESWIC30028AMAFSSWINT.SPEXT.SPQ305Q304SBVP 5VC1VC2Q308Q3013-5. Squelch circuitThe output from IC12 enters FM IC again, then passedthrough a band-pass filter. The noise component output fromIC12 is amplified by Q4 and rectified by D4 to produce a DCvoltage corresponding to the noise level. The DC voltage issent to the analog port of the CPU (IC19). And IC12 outputs aDC voltage (RSSI) corresponding to the input of the IF amplifier.The CPU reads the RSSI signal via pin 93.IC19 determines whether to output sounds from the speakerby comparing the input voltage of pin 91 and pin 93 with thepreset value.Fig. 5 Squelch circuit12DETBPFAMPDETRSSI NOISEAMPIC19CPUIF AMP79193IC12 : FM IF ICQ4 D4Fig. 6 Squelch and RSSI voltage vs ANT input levelSQ closeSQ openPresetvalueANT input levelSQ voltageANT input levelRSSI voltagePreset balue4. Transmitter System4-1. Microphone amplifierThe signal from the internal microphone goes through themute switch (Q300).When the SP-MIC is not attached, the microphone switchingterminal (MSW) on the universal connector becomes High, andmute switch (Q300) is turned ON. When the SP-MIC is