ICOM HM-56A Microphone Schematic Diagram

Circuit Diagram Overview

The diagram illustrates the internal circuitry of the ICOM HM-56A microphone. It details the connections between various electronic components, including integrated circuits (ICs), resistors (R), capacitors (C), diodes (D), transistors (Q), switches (S), and a battery (BT1).

Key components identified include IC1, IC2, and IC3, likely microcontrollers or signal processing units. Various resistors like R1, R12, R22, R23, R13, R14, R15, R16, R17, R19, R20, R21, and R24 are shown, along with capacitors C1 through C18. Diodes D1 and D2 are present, and transistors Q1, Q2, Q3, Q4, and Q5 are indicated. Switches S1, S2, S3, S4, S5, S6, and S7 control various functions such as LOCK, ON/OFF, UP/DOWN, and PTT (Push-To-Talk). A battery BT1 is shown as the power source.

The diagram also features a keypad matrix with numbered and lettered keys (1-9, *, 0, #, A, B, C, D), connected to IC1. Several test points and signal lines are labeled, including MR, LOCK, S.CALL, VER.L, VER.H, RD, PTT, COL1-COL3, ROW1-ROW3, LED, S.PTT, MUTE, NC, T.CALL, TONE, and X.OUT.

A separate section details a test setup with a multimeter (VOM) measuring AC voltage, DC voltage, and resistance (OHM). This setup involves a 9V battery and a 18-ohm resistor.