Icom ic-m506 Service Manual

Also see for IC-M506: Specifications Instruction manual Instruction manual Instruction manual Service manual

Contents

4-1SECTION 4. CIRCUIT DESCRIPTION• RF CIRCUITS• 1ST IF CIRCUITS (For main channels)• 1ST IF CIRCUITS (For CH70)• 2ND IF CIRCUITS (For main channels)• 2ND IF CIRCUITS (For CH70)4-1 RECEIVE CIRCUITSRF CIRCUITS (MAIN UNIT)The RX signal from the antenna is passed through the LPF(L22, L23 and C104–C106), ANT SW (D15), and then ap-plied to the RF AMP (Q101).The amplifi ed signal is divided and applied to the 1st IF cir-cuits for MAIN CH or CH70, through the attenuator (D201,R201 and C201: for MAIN CH) and BPF (FI201: for MAIN CH:FI301: for CH70).1ST IF CIRCUITS FOR MAIN CHANNELS (MAIN UNIT)The RX signal from the RF circuits is applied to the 1st mixer(D202), and mixed with the 1st LO signal, resulting in the30.15 MHz 1st IF signal.The 1st IF signal is amplifi ed by the 1st IF AMP (Q202, Q203),fi ltered by the 1st IF fi lter (FI202 and FI203), and then appliedto the another IF AMP (Q205). The amplified signal is appliedto the 2nd IF circuits.2ND IF CIRCUITS FOR MAIN CHANNELS (MAIN UNIT)The 1st IF signal from the 1st IF circuits is applied to the IF IC(IC201, pin 16). The IF IC contains the 2nd IF mixer, 2nd IFAMP, detector, and so on, in its package.The 1st IF signal is mixed with the 29.7 MHz 2nd LO signalfrom the 2nd LO oscillator (X202), resulting in the 450 kHz2nd IF signal. The 2nd IF signal is passed through the 2nd IFfi lter (FI204) to remove the sideband noise. The fi ltered sig-nal is amplifi ed by the 2nd IF AMP, and demodulated by thequadrature detector with discriminator (X201).The demodulated AF signal is applied to the RX AF circuits,through the AF SW (IC882, pins 4, 3).ANTLPFBPFANTSWBPFATTRFAMPD15FI201 D201Q1011/3MAIN UNITFI301To the 1st IF circuitsTo the 1st IF circuitsTransmit circuitsFrom the RF circuits(MAIN CH)To the 2nd IF circuits(MAIN CH)IFAMP BPFXTAL IFAMP30.15MHzQ205FI202FI203Q202,Q203 D202To the RXAF circuitsFrom the1st IF circuits(MAIN CH)BPFCERAMICBPF NOISEAMPNOISEDET X202X2012ND IFAMPFMDET2ND LOBUFFIC201FI20429.700MHzIC506B/C:IC505D:AFMUTEDe-emphasysIC882B:AFMUTETo the 2nd IF circuits(CH70)From the 1st IF circuits(CH70)IFAMP BPFXTALFI302FI303Q30221.7MHzQ305From the1st IF circuits(CH70)BPFCERAMICNOISEAMPNOISEDETAFMUTEX301DET2ND LO2ND IFIC301BUFFAMPFMFI304To the RXAF i itBPF IC506B/C:IC505C:BPFIC506B/CDe-emphasys1ST IF CIRCUITS FOR CH70 (MAIN UNIT)The RX signal from the RF circuits is applied to the 1st IFmixer (Q302), and mixed with the 134.825 MHz 1st LO signal,which is generated by the VCO (Q3, Q4, D3, and D4), result-ing in the 21.7 MHz 1st IF signal.The 1st IF signal is fi ltered by the 1st IF fi lters (FI302 andFI303), and then applied to the 1st IF AMP (Q305). The am-plifi ed signal is applied to the 2nd IF circuits.2ND IF CIRCUITS FOR CH70 (MAIN UNIT)The 1st IF signal from the 1st IF circuits is applied to the IF IC(IC301, pin 16). The IF IC contains the 2nd IF mixer, 2nd IFAMP, detector, and so on, in its package.The 1st IF signal is mixed with the 21.25 MHz 2nd LO sig-nal, which is generated by the reference frequency oscillator(X101), resulting in the 450 kHz 2nd IF signal. The 2nd IFsignal is passed through the 2nd IF fi lter (FI304) to removethe sideband noise. The fi ltered signal is amplifi ed by the 2ndIF AMP, and demodulated by the quadrature detector withdiscriminator (X301).DSC DECODING CIRCUITS (MAIN UNIT)The demodulated AF (FSK: Frequency Shift Keying) signalis applied to the DSC decoder (LOGIC UNIT: IC12, pin 2),which converts the sub audible tone signal into the serial data,through the LPF (IC514, pins 10, 8) and DSC SW (LOGICUNIT: IC3, pins 7, 1).The serial data is applied to the CPU (LOGIC UNIT: IC1,pin 103) to control the transceiver (emergency alarm, DSCindication and so on.).