Kenwood TK-885 Service Manual

Also see for TK-885: Instruction manual Service manual

21TK-885CIRCUIT DESCRIPTION /Fig. 2 Receiver system / Wide/Narrow Changeover CircuitThe W/N port (pin 11) of the shift register (IC7) is used toswitch between ceramic filters. When the W/N port is high,Q24 turns on and the ceramic filter SW diode (D22, D23) CF1turns on to receive a Wide signal. At the same time, Q16turns on and one of the filters is selected so that the wideand narrow audio output levels are equal.When the W/N port is low, Q23 turns on and the ceramicfilter SW diode (D22, D23) CF2 turns on to receive a Narrowsignal. AF Signal SystemThe detection signal (DEO) from the TX-RX unit goes tothe audio processor (IC504) of the control unit. The signalpasses through a filter in the audio processor to adjust thegain, and is output to IC502. IC502 sums the AF signal andthe DTMF signal and returns the resulting signal to the TX-RXunit. The signal (AFO) sent to the TX-RX unit is input to the D/A converter (IC5). The AFO output level is adjusted by the D/A converter. The signal output from the D/A converter is addedwith the BEEP signal (BPO) and the resulting signal is inputto the audio power amplifier (IC10). The AF signal from IC10switches between the internal speaker and speaker jack (J1)output.Fig. 4 AF signal system /LPFANTBPF BEFQ201AMPQ15AMPIC2AMPIC200MIXXF1BPFD211D209,210ANTSW +Q203AMPBPFCF1/CF2IC11MIX,IF,DETX22ndlocal OSC1st localOSC (HT)DEOCF1(Wide)CF2(Narrow)IFIMXOIC11IF systemAFODETOUTC107C100C108R114R123R133R126 R125R130R131++Q16DMQ32 R121W/NIC7 11pinWide : HNarrow : LC118D22 D23Q235CQ24Wide : LNarrow : HFig. 3 Wide/Narrow changeover circuitAUDIOPROCE.SUMAMPD/ACONV.IC504 IC502 IC5AF PAIC10 SPDTMF BPOAFODEOCONTORL UNIT