Kenwood TK-3140 Service Manual

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TK-31407CIRCUIT DESCRIPTIONFig. 3 Wide/Narrow changeover circuitQ201IC200Q202AFOUT5RR213R210CF201CF200 D202 D203R208R216R211C206C210MIXOUTAFOUTQUADIFOUTIFIN C221R255R221CD200R264R256W/N5CNSR2223-4. Audio amplifier circuitThe demodulated signal from IC200 goes through the muteswitch (Q204) and is amplified by IC300 (2/2), high-pass filtered,low-pass filtered, high-pass filtered, band-eliminate filtered, andde-emphasized by IC500.The signal then goes through an AF amplifier IC305 (2/2),an electronic volume control (IC307), and an AF switch (Q308is on), and is routed to audio power amplifier (IC313), where itis amplified and output to the internal speaker.The audio mute signal (AM1) from the shift register becomesLow in the standby and Q302, Q303 which are power supplycircuit for IC313 turn off. Also, IC500 is set to the power downmode according to data from microprocessor, and the AF signalis muted. When the audio is output, AM1 becomes High toturn Q302, Q303 ON, and voltage is supplied to power terminalVP of IC313. Also, IC500 is canceled out of the power downmode.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 (Q308)is turned ON, and the AF signal is input to both amplifiers ofIC313.When SP-MIC is attached, SSW is connected to GND atinside of SP-MIC. For this reason, Q308 is turned OFF, andthe AF signal is input only to amplifier for EXT SP of IC313.Change of INT/EXT SP refer to Fig. 4.Center Frequency Nominal 455kHzBand Width 6dB Min. ±4.5kHz40dB Max. ±10.0kHzStop Band Attenuation ±100kHz Min. 25.0dBRipple Within 455±3.0kHz Max. 1.5dBInsertion Loss at 455 kHz Max. 6.0dBTable 2 Ceramic filter (L72-0996-05): CF2013-3. Wide/Narrow changeover circuitNarrow and Wide settings can be made for each channelby switching the ceramic filters CF200 (Wide), CF201 (Narrow).The WIDE (high level) and NARROW (low level) data isoutput from IC311.Regardless of NARROW or WIDE band selection, signalsalways pass through the filter, CF200.When the WIDE band is selected, Q201 is turned ON, thenD202 and D203 are turned OFF.So, the signal does not pass through the filter CF201. Whenthe NARROW band is selected, Q201 is turned OFF, then D202and D203 are turned ON. So, the signal passes through thefilters, CF200 and CF201.Q202 turns on/off with the Wide/Narrow data and the IC200detector output level is changed to maintain a constant outputlevel during wide or narrow signals.AM1 SSW VC1 VC2 SPH H H L INTH L L H EXTL H L L MUTEL L L L MUTESWIC31328AM1AFSSWINT.SPEXT.SPQ303Q302SBVP 5VC1VC2Q307Q305Fig. 4 Audio amplifier circuit