Telex AIRMAN 8+ - Microphone Total Harmonic Distortion (THD) Test; Speaker Troubleshooting

AIRMAN 8+ Maintenance | en 19
Bosch Security Systems, LLC
Customer Maintenance Manual
2024-11 | 07 | F.01U.387.060
5.3.5 Microphone total harmonic distortion (THD) test
1. Calibrate the sound pressure to be 114dB SPL at 6mm from an artificial mouth.
2. Measure the THD of the microphone placed at that location using the same test circuit.
It meets the TSO spec when THD is less than 5% from 350Hz to 6000Hz.
5.4 Speaker troubleshooting
Physically inspect
the overhead cable
Physically inspect
the speaker wires
Physically inspect
speaker wires
Is the main cable
in good condition?
Is the overhead cable
in good condition?
Are the speaker wires
in good condition?
Are the Speaker wires
in good condition?
Are the solder points
in good condition?
Test complete
Replace the
main cable
Are the solder points
in good condition?
Yes
Yes
Check the solder points
at the speaker and at the
board
Check the solder points
on the boom side PCBA
Yes
Measure resistance
of speaker
Yes
Yes
Yes
No
No
No
Boom side Non Boom side
Is mic circuitry
validated?
No Yes
Physically inspect
the main cable
Did failure occure
in both speakers?
Do the speakers
pass the talk test?
Replace the boom side
speaker wires
No
Replace the non-boom
side speaker wires
No
Replace the non-boom
side speaker wires
Is the resistance good?
Test the PCBA
Test sensitivity and
frequency response
Yes
No
Replace the speaker
No
Replace the
speaker wires
No
Replace the
speaker
No
Replace the
PCBA
Check the solder points
at the speaker and at
the board
Measure resistance
of the speakers
Yes
Yes
Yes
Yes
Yes
Test the PCBA
Are the solder points
in good condition?
Yes
Yes
Yes
No
Resolder the main cable
to the PCBA
Test the boom side
PCBA
Measure continuity
from plug to PCBA
Is the resistance good?
Did the PCBA pass?
No
Replace the boom side
PCBA
Validate the non boom
side PCBA
Yes
Replace the speakers
No
No
No
Replace the cable
No
Replace the non boom
side PCBA
Did the PCBA pass?
Is the PCBA working?
Is the continuity good? Do the speakers work?
No
Replace the
PCBA
Did the PCBA pass?
Did both speakers pass
sensitivity and response?
Speaker test complete
Figure5.3: Speaker Troubleshooting