Icom IC-M401EURO Service Manual

Also see for IC-M401EURO: Instruction manual

Contents

4 - 44-4 ATIS AND DSC CIRCUITS4-4-1 ATIS ENCODE CIRCUIT ([HOL], [FRG] ONLY)(LOGIC BOARD AND MAIN UNIT)The FSK signal of ATIS created at CPU (IC1) is passedthrough the ladder type D/A convertor (R55–R73) to convertinto the analog signal. The analog signal is applied to thebuffer amplifier (Q8), and then applied to the mixer circuit(MAIN unit; IC10A, pin 2) to mix with signals from the micro-phone. The signal passes through the low-pass filter (MAINunit; IC10B, pins 5, 7) and is then applied to the VCO circuitas modulation signal.4-4-2 DSC ENCODE CIRCUIT (MAIN UNIT)The DSC signal created at the optinal DSC controller (DS-100) is applied to the T1 via the J7, and then as floating sys-tem output. The signal is applied to the buffer amplifier(Q29), and then passes through the 6 dB/oct pre-emphasiscircuit (C282, C233, R203, R207). The signal is applied tothe mixer circuit (IC10A, pin 2) to mix with signals from themicrophone. The signal passes through the low-pass filter(IC10B, pins 5, 7) and is then applied to the VCO circuit asmodulation signal.4-5 LOGIC CIRCUITS (LOGIC BOARD)• CPUIC1 is an 8 bit signal chip micro-computer and contains LCDdriver, serial I/O, timer, A/D converter, programmable I/O,ROM and RAM.• SYSTEM CLOCK CIRCUITX1 is a ceramic oscillator and oscillate 9.8304 MHz systemclock for the CPU (IC1).• RESET CIRCUITIC6 is a reset IC. When turn power ON, IC6 outputs a resetsignal (“LOW” pulse) to the CPU (IC1, pin 15) via the “RES”line.• LOW BATTERY DETECTORVCC voltage is divided by R74, R75 and is applied to the lowbattery detector section in the CPU (IC1, pin 91) via the“LBAT” line.• DIMMER CIRCUITCPU (IC1), Q2, Q3 and Q4 are dimmer circuit and controlthe 4 steps the LCD backlight (DS3–DS8).-4-6 POWER SUPPLY CIRCUITSVOLTAGE LINESLINEHVHVSVCC5VT5R5DESCRIPTIONThe voltage from the connected DC power sup-ply.Same voltage as the HV line which is passedthrough the [PWR] switch (VR-A board; R1).Same voltage as the HVS line. The voltage isapplied to the optional DSC controller (DS-100).Common 5 V converted from the VCC line at the5V regulator circuit (MAIN unit; IC8).Transmit 5 V controlled by the T5 control circuit(MAIN unit; Q24, Q25) using the “SEND” signalfrom CPU (LOGIC board; IC1). The controlledvoltage is applied to the transmitter circuit.Receive 5 V controlled by the R5 control circuit(MAIN unit; Q22, Q23) using the “RCV” circuitfrom CPU (LOGIC board; IC1). The controlledvoltage is applied to the receiver circuit.