Icom ic-m506 Service Manual

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

Contents

4-3• TX AMP CIRCUITS• MIC AMP CIRCUITS• TX AF CIRCUITS• MODULATION CIRCUITSMODULATION CIRCUITS (MAIN UNIT)The MIC signal from the TX AF circuits is applied to the VCO(Q3, Q4 and D2–D4). The modulation signal is applied to D2,to obtain Frequency Modulation.The modulated VCO output signal is passed through the buf-fers (Q5 and Q7), and then applied to the TX AMP circuits asa TX signal, through the LO SW (D7).TX AMP CIRCUITS (MAIN UNIT)The TX signal is amplifi ed by the YGR (Q21) and power AMP(IC1), and then passed through the TX output power detec-tor (D12 and D13), ANT SW (D14), and LPF (L22, L23 andC104–C106), before being sent to the antenna.APC CIRCUITS (MAIN UNIT)The voltage produced at the LPF (L21, C101 and C102) isrectifi ed by D12 and D13, and is used as the TX power sens-ing voltage.The voltage is applied to the APC AMP (IC2, pin 3), and theoutput voltage controls the gate bias voltage of power AMP(IC1) to keep the TX output power constant.4-2 TRANSMIT CIRCUITSTX AF CIRCUITS (MAIN UNIT)The AF signal from the microphone (MIC signal) is passedthrough the MIC mute SW (IC502, pins 1, 2), and then ap-plied to the MIC AMP (IC513, pin ).The MIC signal from the HM-195/HM-205RB is passedthrough the ATT (R531 and R532), MIC mute SW (IC502B,pins 4, 3), and then applied to the MIC AMP (IC513, pin ).TX AF CIRCUITS (MAIN UNIT)The amplifi ed MIC signal is applied to the noise canceller IC(IC901, pin 28).The processed MIC signal is output from pin 36, passedthrough the AF SW (IC505, pins 8, 9), and then applied to theD/A converter (IC19, pin 22) to be adjusted in level.The level-adjusted AF signal is output from pin 23, andpassed through the AF MUTE SW (IC882, pins 8, 9), andthen applied to the IDC AMP (IC513B, pin 6), which limits theamplitude of MIC signal to prevent the over deviation. Theamplitude-limited signal is output from pin 7, and passedthrough the LPF (IC513C, pins 10, 8), and then applied to themodulation circuits.HM-195/HM-205RBHM-205BHM-195AFMUTEMICAMPAFMUTEATTMIC-INMAIN UNITFRONT UNITIC513ATo the TX AF circuitsIC502IC502BOPTIONALCOMMANDMICTX/RXSWD7,D8:BUFFBUFFVCOFrom theTX AF circuitsTo theTX AMP circuitsQ5D 3,D4SHIFTQ2D1 Q7Q8ANTLPFANTSWYGRAMP PWRAMP LPFQ21D14,D15IC1:D16From the modulationcircuitsRX circuitsPre-emphasys LPFD/AFrom theMIC AMP circuits To the modulationcircuitsIC513CNOISECANCELLERIC901 IC505DAFAFMUTE SWIC882CIC19 IC513BIDC