Kenwood TK-2180 Service Manual

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TK-218083-3. Wide/Narrow switching circuitWide and Narrow settings can be made for each channelby switching the ceramic filters CF201 (Wide), CF200 (Nar-row). The Wide (low level) and Narrow (high level) is outputfrom IC502.When a Wide (low level) is selected, Q200 (N-ch) turn offand Q200 (P-ch) turn on. When a Narrow (high level) is se-lected, Q200 (N-ch) turn on and Q200 (P-ch) turn off. D201and D203 are switched to ceramic filters when a high/lowlevel is selected.Q204 turns on/off with the Wide/Narrow and the IC200detector output level is changed to maintain a constant out-put level during wide or narrow signals.When SP-MIC is attached, SSW is connected to GND atinside of SP-MIC. For this reason, Q618 is turned off, and theAF signal is input only to amplifier for EXT SP of IC609.Change of INT/EXT SP refer to Fig. 4.AM1 AM2 SSW VC1 VC2 SPH L H H L INTH L L L H EXTL H H L L MUTEL H L L L MUTEMXOAFOUTQUADIFOUTIFI W/N5RD314C201C200C215C217R208R211R215R212R209C209R205Q200 D201 D203CF200CF201IC200R222R224Q204R225 5CAFOUTW/NCD200“H” : Narrow“L” : WideFig. 3 Wide/Narrow switching circuitSWSWQ618VC12VC28BAFAM1SSWAM2Q616(1/2) Q617Q605Q613Q6125VPIC609IC605IC607INT.SPEXT.SPAF3-4. Audio amplifier circuitThe demodulated signal from IC200 goes through themute switch (Q203), IC600 (1/2) and IC606, high-pass fil-tered, low-pass filtered, high-pass filtered and de-empha-sized by IC607.The signal then goes through mute switch (Q605 1/2), andan electronic volume control (IC605), and an AF switch (Q618is on), and is routed to audio power amplifier (IC609), where itis amplified and output to the internal speaker.The audio mute signal (AM1) from the IC502 becomesLow in the standby and Q612, Q613 which are power supplycircuit for IC609 turn off. Also, the audio mute signal (AM2)becomes High to turn Q605 (1/2) off. When the audio isoutput, AM1 becomes High to turn Q612, Q613 on, and volt-age is supplied to power terminal VP of IC609. Also, AM2becomes Low to turn Q605 (1/2) on.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 (Q618)is turned on, and the AF signal is input to both amplifiers ofIC609.3-5. Squelch circuitThe output from IC200 enters FM IC again, then passedthrough a bandpass filter. The noise component output fromIC200 is amplified by Q201 and rectified by D202 to producea DC voltage corresponding to the noise level. The DC volt-age is sent to the analog port of the CPU (IC502). And IC200outputs a DC voltage (RSSI) corresponding to the input of theIF amplifier. The CPU reads the RSSI signal via pin 125.IC502 determines whether to output sounds from thespeaker by comparing the input voltage of pin 124 and pin125 with the preset value.DETBPFAMP DETNOISEAMPIF AMPRSSI127Q201 D202IC200 : FM IF ICIC502CPU125124SQ close Presetvalue PresetvalueANT input level ANT input levelSQ voltageRSSI voltageSQ openFig. 4 Audio amplifier circuitFig. 5 Squelch circuitFig. 6 Squelch and RSSI voltage vs ANT input levelCIRCUIT DESCRIPTION