Kenwood TK-190 Service Manual

Also see for TK-190: Pricing and specification manual Service manual Service manual Instruction manual Instruction manual

Contents

13TK-1903-4. Audio amplifier circuit• TX-RX unitThe demodulated signal from IC300 goes through IC301,and is amplified by IC601 (2/2), high-pass filtered, low-passfiltered, high-pass filtered, band-eliminate filtered, and de-emphasized by IC607.The signal then goes through an electronic volume con-trol (IC603), an AF amplifier IC604 (2/2), and an AF switch(Q8 is on and Q7 is on of the control unit), and is routed toaudio power amplifier (IC1 of the control unit), where it isamplified and output to the internal speaker.• Control unitThe audio mute signal (AMP SW) from the microproces-sor becomes Low in the standby and Q5, Q6 which arepower supply circuit for IC1 turn off. When the audio is out-put, AMP SW becomes High to turn Q5, Q6 on, and voltageis supplied to power terminal VP of IC1.Speaker switching is done from IC403 (TX-RX unit) by INTAFC or EXT AFC. First, the logic level at the speakersswitching terminal (SSW) on the universal connector is inputto the microprocessor (IC406 TX-RX unit). The microproces-sor then outputs data to IC403 based on this input.When there is no SP-MIC installed, this logic level is high.When the INT AFC is high, the EXT AFC goes low, so the AFsignal is only input to the amplifier for the internal speaker(INT SP) of IC1. However, when a SP-MIC has been in-stalled, this logic level is low, so the INT AFC goes low andthe EXT AFC goes high. So that the AF signal is input only toamplifier for the external speaker (EXT SP) of IC1.IC300FM IF SYSTEM129.005MHz CF300455kHzSWIC301IC601(2/2)AF AMPBEFHPFLPFHPFDE-EMP EXP MUTE52 141VOLIC603IC604(2/2)AF AMPAFAFIC607SWQ8SWSWQ7INT AFCEXT AFCINT.SPEXT.SP426813169125IC1SWSBAMP SWQ5,6Fig. 3 Audio amplifier circuit3-5. Squelch circuitIt amplifies the demodulated noise signal from FM IC(IC300) after filtering through BPF circuit. Then, the ampli-fied signal is coverted to DC signal by the detection circuit.The coverted signal is feeded through the microprocessor(IC 406) and the voltage level is detected by ADC (A/D con-verter) to control the squelch circuit.IC300AFOUTNOISEAMPQ304BUSYCPUOUTPUTEXPANDERIC40642789IC403AMP SWINT AFCEXT AFCDETD301NOISEAMPDETOUTFig. 4 Squelch circuitCIRCUIT DESCRIPTION