Section II. DETAILED THEORY OF OPERATION

TM 11-5895-1141-34

Section II. DETAILED THEORY OF OPERATION

SECTION CONTENTS

PAGE

General

Headset/Microphone Jack Panel Assembly

Audio Unit Assembly

Microphone Amplifier/Lamp Brightener Module Assembly

Selector Unit Assembly

Selector Module Assembly

Volume Control Module Assembly

Speaker Amplifier Assembly

Recorder Monitor Module

2-3. GENERAL

This section contains the detailed theory of operation of the replaceable units and modules contained in the console. They

are the following: headset/microphone jack panel assembly, audio unit assembly, microphone amplifier/lamp brightener

module assembly, selector unit assembly, selector module assembly, volume control module assembly, speaker amplifier

assembly, and recorder-monitor module.

a. Headset/Microphone Jack Panel Assembly. Refer to figure FO-4. For the sake of brevity, the basic component

part numbers are used in place of the actual part numbers. On this unit, the basic number if added to 300, results in the

actual part number. Thus, connector P1 is actually P301. The jack panel consists of a panel in which are mounted

receptacles for the microphone or headset to be used. The assembly includes a circuit board. The circuit board mates

with the audio unit assembly via a cable card connector P1. The connectors and associated circuitry are as follows:

(1) Telephone Jacks J1 and J2. These are standard twin three wire plugs (JAN type PJ-511). The associated

circuits are intended for operation with a Plantronics HS-O111 or equivalent headset. Resistor R1 in conjunction with the

microphone bias circuits provides a matching 50 ohm load for the microphone. Capacitor C1 prevents the passage of dc

from the biasing circuit through R1. Resistors R3 and R4 provide the bias current for the headset microphone. The

microphone is connected to the tip terminals, and the earphone to the sleeve terminals of the phonejacks. The twin plug

may be inserted either way into J1 and J2.

(2) Connector J3. This is a 5-pin connector for use with an M-80C low level (-50 dBm) microphone which

requires no bias current. The microphone connects to the 200 ohm side of the microphone matching transformer T1201

located in the microphone amplifier/lamp brightener module, via J3-D and P1-A. The transmitter keying switch on the

microphone connects to J3-A. Pin C is the common return.

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