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LH-4 MANUAL

POWER ON-OFF

The Power on-off switch controls 12 volts DC power to the internal circuitry. The POWER lamp will light when the ON/OFF switch is in the ON position and power is applied to the LH-4 circuits.

TONE ON-OFF

Activates the TONE Generator for microphone or headphone testing.

TONE LAMP

Lamp is lit when TONE generator is active.

TONE LEVEL

Controls the audio output level of the TONE generator. The control should be in the counter clockwise position when TONE generator is turned on due to the high level output available.

HEADPHONE

Jack for connection of headphone or headset headphone plug. Disconnects SPEAKER when phone plug is inserted. Accepts M642/4-1 (PJ-055B) plug.  Also accepts U-93A/U plug.

MICROPHONES switch

CARBON/EQUIVALENT position

DYNAMIC position

Selects test circuitry for type of microphone to be tested. CARBON/EQUIVALENT position should be used on most microphones this includes power dynamic microphones.

DYNAMIC position should only be used when the microphone is known to be an unpowered type dynamic mike.

MIKE LEVEL

Adjusts the gain of the microphone test circuitry. This control, in conjunction with the METER, is used to determine relative signal output of microphone.

MICROPHONE JACK

The Microphone Jack is for the connection of microphone or headset microphone to be tested. Accepts M642/5-1 (PJ-068) plug.

KEY ON LAMP

Lamp indicates when microphone or headset transmit button is depressed.

HELICOPTER JACK

The Helicopter Jack is for the connection of helicopter microphone or headset microphone to be tested. Accepts U-93A/U and U-174/U plugs.

MICROPHONE TESTS VOICE

All meter readings specified in these procedures are approximate.

A microphone of known good condition should be used with each

procedure before testing units of unknown condition to determine normal meter readings and operation.

The LH-4 should be connected to suitable AC source.

TONE ON-OFF should be OFF. MIKE LEVEL should be full counter

clockwise (CCW). Turn unit on with POWER ON-OFF switch. POWER

lamp should light.

WITH HEADPHONES CONNECTED

Select CARBON/EQUIVALENT or DYNAMIC position for type of

microphone to be tested. Connect Microphone to MICROPHONE Jack.

Connect headphones to HEADPHONE Jack. Depress mike activate

(transmit) button or switch. KEY lamp should light. (Some

headsets or headset mikes do not require the use of mike activate

button or switch.) Speak into microphone while increasing MIKE

LEVEL. METER needle should indicate approximately .1 to .25 with

up to 1/2 scale (.5) possible on some strong sounds.

Due to the characteristics of the human voice the meter will not

maintain a steady reading but will bounce up and down. We have

designed into the tester, circuits to smooth this bouncing as much

as possible while maintaining a meter reading representative of

the microphone output. Usual METER reading of about .1 to .25 should be displayed on normal speech with peaks of 1/2 scale (.5)

on strong sounds at full clockwise (CW) setting of the MIKE LEVEL

control. Whistling into the mike can peg the METER.

Output will be heard in headphones. Listen to audio and check

clarity (no distortion) and noise (none). Return all controls to

Beginning Settings when testing is complete.

 

WITHOUT HEADPHONES CONNECTED

LH-4 POWER to ON. TONE to OFF. MIKE LEVEL full CCW.

Select CARBON/EQUIVALENT or DYNAMIC position. Connect microphone to MICROPHONE jack.

Some headset microphones do not require the use of (Mike Key)

Transmit button or switch when testing microphone. IF the unit

has a Key or Transmit switch, activate the switch and KEY lamp

will light.

Speak into microphone while increasing MIKE LEVEL. To avoid feedback, keep the microphone away from panel speaker . Noise canceling microphones can be checked, by pointing the noise canceling-

aperture toward the speaker. Any feedback should be eliminated if

noise canceling is functioning properly. Microphone audio

will be heard in the SPEAKER.

Listen to audio and check for clarity (no distortion) and noise

(none). If MIKE LEVEL can be increased to full CW without

feedback, METER readings of .1 to .25 should be displayed on

normal speech with peaks of 1/2 scale (.5) on strong sounds.

Whistling into the mike can peg the METER.

Return all controls to Beginning Settings when testing is completed.

 

MICROPHONE TESTS with TONE GENERATOR

Connect the LH-4 to a suitable AC source. TONE ON-OFF

should be OFF. Turn unit on with POWER ON-OFF switch.

POWER lamp should light.

Select CARBON/EQUIVALENT or DYNAMIC position for type of

microphone to be tested. Set TONE LEVEL CCW (counterclockwise)

Set MIKE LEVEL full CW.

Connect Microphone to MICROPHONE Jack. Turn TONE on. TONE lamp

will light. Adjust TONE LEVEL to approximately 3/4 full CW.

TONE audio will be heard in SPEAKER (LOUD). Some headset

microphones do not require the use of Transmit button or switch

when testing microphone. Key the Microphone, if necessary, and

place Mike (Voice admitting side of mike toward speaker)

approximately one inch from SPEAKER. MIKE KEY lamp should light

if a mike keying switch or button is used. METER should read full

scale.

After testing is completed decrease TONE LEVEL and MIKE LEVEL to

full CCW and turn TONE off. CAUTION Failing to decrease MIKE

LEVEL when turning off TONE will allow Mike to SPEAKER feedback

and squealing if the microphone is still active.

Return all controls to Beginning Settings when testing completed.

 

HEADPHONE TEST USING TONE

Connect LH-4 to suitable AC power source. TONE should be OFF.

TONE LEVEL full CCW (counter clockwise). MIKE LEVEL full CCW.

Turn unit on with POWER ON-OFF. POWER lamp should light.

CAUTION - DO NOT CONNECT HEADPHONES UNLESS TONE LEVEL

IS FULL COUNTER CLOCKWISE.

Connect headphones plug to HEADPHONES Jack. Turn TONE ON.

TONE LAMP will light. Listen for TONE audio in headphones

while very slowly increasing TONE LEVEL to comfortable level.

This level should be about 1/4 to not more than 1/2 turn on the

TONE LEVEL control. Audio in the headphones should be clear,

no distortion or noise.

Return all controls to Beginning Settings when tests are

completed.

 

HEADPHONE TESTS USING MICROPHONE

Perform MICROPHONE TEST - VOICE, WITH HEADPHONES CONNECTED

using microphone or headset with microphone of known good

condition.

 

PLUGS, CORDS, TRANSMIT SWITCH TESTS

Plugs, Cords, and Transmit Switches can be checked while testing

any unit with which they are associated. Noise, intermittent

operation or failure to operate properly are some of the problems

caused by the items.

HEADSET TEST

HEADPHONES, BOOM MIKE & TRANSMIT SWITCH

Connect LH-4 to suitable AC Source. TONE to OFF.

TONE LEVEL to CCW. Select CARBON/EQUIVALENT or DYNAMIC for type

of microphone. MIKE LEVEL to CCW. Turn the unit on with POWER

ON-OFF switch. POWER lamp should light.

Connect Headphones to HEADPHONE jack, Microphone transmit

switch assembly to MICROPHONE jack and Boom mike plug to

Transmit Switch Assembly. ASSURE TONE LEVEL is full CCW.

Turn TONE to ON. TONE lamp will light. Increase TONE LEVEL

slowly to comfortable level. This should be about 1/4 to no

more than 1/2 turn on TONE LEVEL control. TONE audio should

be heard in both headphones. Cords and connections can now

be checked.

When finished return TONE LEVEL to full CCW and TONE switch to

OFF. TONE lamp should go off.

Depress Transmit button, KEY lamp should light. Increase

MICROPHONE LEVEL to full CW. Spoken audio and background noise

should be heard in headphones, METER will also indicate. Cords,

Connections and Transmit switch can now be checked while

monitoring KEY lamp and Headset audio.

Return MIKE LEVEL to full CCW. Move POWER switch to OFF and

disconnect Headset plugs when test are completed.

  Avionics Test Equipment Panels and Cables for bench testing of Aircraft Radio, Navigation, Audio Controllers, Radar and more. Linaire Engineering Inc.
Last modified: June 15, 2004