Telex AIRMAN 8+ - Validate MIC Circuitry; Microphone;Amplifier Sensitivity Test; Microphone Sensitivity Adjustment

18 en | Maintenance AIRMAN 8+
2024-11 | 07 | F.01U.387.060
Customer Maintenance Manual
Bosch Security Systems, LLC
5.3.2 Validate mic circuitry
To validate the mic PCBA, do the following:
1. Construct a test circuit.
2. Connect the test circuit to the microphone plug of the headset.
For more information, see Connectors.
3. Apply an audio signal/excitation to the microphone.
If audio signal is detected, the board is valid.
If audio signal is not detected, the board should be replaced.
5.3.3 Microphone/amplifier sensitivity test
i
Notice!
This headset was designed, tested, and approved to FAA TSO C139a. The TSO requires the
headset meet the minimum performance specifications as defined in RTCA DO-214A. This
document and specifications listed here reference the test procedures, product settings,
and equipment used as defined in these standards. Refer to the standard for details on how
to perform individual tests.
To test sensitivity of the microphone, do the following:
1. Calibrate an artificial mouth to generate 94dBSPL for 1kHz tone at 6mm from the
center of its opening.
2. Using the test circuit from the mic validation and TSO procedures, measure the output
of the headset microphone with a true RMS AC voltmeter.
i
Notice!
Microphone output should be -28±3dBV. If not, make adjustment following section 5.3.4.
5.3.4 Microphone sensitivity adjustment
The microphone gain has been factory-adjusted to the nominal level required for normal
radio operation. Microphone sensitivity adjusts by turning the gain adjustment control.
To adjust the microphone, do the following:
1. Rotate the boom mic clockwise until the microphone gain adjustment access hole is
aligned and open.
2. Insert a 2mm x 0.5mm flat-bladed screwdriver into the gain adjustment access hole.
i
Notice!
If the gain adjustment access hole is properly aligned, the screwdriver can be inserted
approximately ½-inch into the hole. If not properly aligned, the screwdriver only inserts
approximately 1/8-inch into the hole.
3. Turn the gain adjustment potentiometer clockwise to increase the gain.
OR
Turn the gain adjustment potentiometer counterclockwise to decrease the gain.