Airman 750 - Headset Telex - Free user manual and instructions

Product Type	Aviation Headset
Brand	Telex
Model	Airman 750
Connectivity	Wired with dual plug (PJ-068 and PJ-055)
Impedance	150 ohms per ear
Frequency Response	100 Hz - 10 kHz (microphone), 100 Hz - 6 kHz (speaker)
Noise Attenuation	Passive NRR 23 dB
Microphone Type	Electret condenser, noise-cancelling
Microphone Impedance	500 ohms
Weight	340 g (12 oz)
Headband	Adjustable, padded
Earcups	Over-ear, foam-filled, leatherette cushions
Cable Length	5 ft (1.5 m) straight cable
Features	Volume control, noise-cancelling microphone, gel-filled earpads
Maintenance	Clean with mild soap and water; avoid solvents
Safety	Compliant with ANSI S3.19-1974 (hearing protection)
Warranty	1 year limited
Certification	FCC Part 15

Frequently Asked Questions - Airman 750 Telex

How do I connect the Airman 750 to an aircraft?

Plug the dual plugs into the aircraft's intercom jacks: the larger PJ-068 for headset and smaller PJ-055 for microphone. Ensure volumes are low before connecting.

Can I use this headset with a smartphone?

The Airman 750 is designed for aircraft intercom systems. For use with smartphones, you need an adapter like a U174 to 3.5mm cable.

How do I clean the ear cushions?

Remove the cushions and hand wash with mild soap and water. Let them dry completely before reattaching. Do not machine wash.

What is the battery requirement?

The Airman 750 is a passive headset and does not require batteries. It receives power from the aircraft's intercom system.

Does it have active noise cancellation?

No, the Airman 750 uses passive noise attenuation through robust ear cups and foam padding to reduce ambient noise.

Are replacement parts available?

Yes, Telex offers replacement ear cushions, headband pads, and cables. Contact authorized dealers or Telex support.

What is the warranty period?

The Airman 750 comes with a 1-year limited warranty against defects in materials and workmanship.

Can I use it for general aviation and helicopter?

Yes, it is suitable for both fixed-wing and rotary-wing aircraft, as long as the intercom system uses standard dual plugs.

How to adjust the headband for a better fit?

Slide the adjustment arms up or down to match your head size. The headband should sit snugly without pressure points.

Is the microphone flexible?

Yes, the microphone boom is adjustable and flexible to position the mic near your mouth for optimal voice clarity.

USER MANUAL Airman 750 Telex

Black-and-white photo of a dual-camera headset with earbuds and antenna (no text or symbols visible)

en

Customer Maintenance Manual

Table of contents

1	General information 5
1.1 Record of Revisions 5
1.2 Purpose of manual 5
1.3 Technical support 5
1.4 Parts ordering 5
1.5 Repairs 6
2	Description and specifications 7
2.1 General description 7
2.2 Models covered 7
2.3 Specifications 8
3	Parts list 10
3.1 General 10
3.2 Airman 760, catalog number 64400-200 10
3.3 Airman 750, catalog number 64300-200, -205, -208, -210, -212, -218, -219, -220, and -300 11
4	Disassembly and assembly	14
4.1 Disassembly	14
4.1.1	Removal of the receiver assembly	14
4.1.2	Removal of the cord assembly 15
4.1.3	Removal of the circuit board and boom assembly (Airman 750)	16
4.1.4	Removal of a glider	16
4.2 Assembly	16
5	Wiring and connectors	17
5.1 Airman 750 wiring diagrams	17
5.1.1	Catalog numbers 64300 -200, -220, -300	17
5.1.2	Catalog number 64300 -210	18
5.1.3	Catalog numbers 64300 -205, -208	18
5.1.4	Catalog number 64300 -212	19
5.1.5	Catalog number 64300 -218	19
5.1.6	Catalog number 64300 -219	20
5.2 Airman 760 wiring diagrams	20
5.2.1	Catalog number 64300 -200	20
5.3 Airman 750 connectors	20
5.3.1	Connector view for catalog numbers 64300-200, -212, -300	20
5.3.2	Connector view for catalog numbers 64300-205, -208, -210	21
5.3.3	Connector view for catalog number 64300-218	21
5.3.4	Connector wiring diagram for catalog number 64300-219	22
5.3.5	Connector wiring diagram for catalog number 64300-220	22
5.4 Airman 760 connectors	22
5.4.1	Connector view for catalog number 64400-200	22
6	Maintenance	24
6.1 Microphone validation and adjustment	24
6.1.1	Microphone and amplifier sensitivity check	24
6.1.2	Microphone sensitivity adjustment	25
6.1.3	Microphone total harmonic distortion (THD) test	26
6.2 Circuit board - 200/300 Series Airman 750	26
6.2.1	Testing the circuit board assembly	26
6.3 Speaker validation 26
6.3.1	Speaker sensitivity and frequency response verification	26

7 Troubleshooting 29

7.1 Troubleshooting chart 29

1 General information

1.1 Record of Revisions

Rev No Revision Date Change Description
A 12/1988	See previous revisions of 38108-965 for affected changes
B 06/1989
C 01/1990
D 11/1993
E 03/1995
F 04/1996
G 06/2000
7 07/2017 This document was completely rewritten and a Bosch part number (F.01U.311.532) was assigned.
8 09/2017 – Updated revision on front cover– Removed the Insertion Date column from this table– Technical Support Contact information updated– In the models covered table, updated part number type-o
9 08/2018 – Minor formatting and parts list update
10 04/2022 – Update format

1.2 Purpose of manual

This manual, Bosch part number F.01U.311.532, contains information for the overhaul and servicing of the Airman 750/760 headset.

1.3 Technical support

A liaison between the customer and factory is provided by the Bosch Product Support Department. Consultation and assistance on technical problems, part information, and availability of local and factory repair facilities is available. When writing, include all information concerning problem and mail to:

Bosch Communications, LLC

8601 Cornhusker Hwy

Lincoln, NE 68506 U.S.A.

Attn: Aircraft Product Support Mgr.

Telephone: [phone]

1.4 Parts ordering

Replacement parts may be ordered from our parts department. When ordering, please include the following information:

• Model Number
• Part Description
• Part Number
• Quantity

Mail to:

Bosch Communications, LLC

8601 Cornhusker Hwy

Lincoln, NE 68507 U.S.A.

Attn: Parts department

Telephone: [phone]

Fax: [phone]

E-mail: [e-mail]

1.5 Repairs

In order to maintain the FAA certification, all repairs to the headset must be made only by persons authorized under Part 43 of the Federal Aviation Agency regulations. Bosch offers full support and repair.

2 Description and specifications

2.1 General description

The Telex Airman 750 Headset and the Airman 760 Headphone are designed and engineered for high-quality aircraft communications. The Airman 750 is approved for aircraft use under the Federal Aviation Agency TSO C57a and C58a. The Airman 760 is approved for aircraft use under the Federal Aviation Agency TSO C57a.

The Airman 750 Headset features a miniature, noise-canceling electret microphone element which provides superior hum rejection. The microphone is mounted upon a boom which pivots 310 degrees for use on either side of the user's head. The headset amplifier has an adjustable gain control and provides output levels equivalent to carbon microphone levels. Several variations of the 750 headset exist; each model has a different connector and a unique wiring diagram.

The Airman 760 Headphone is designed for users who operate hand-held microphones. The 760 is virtually identical to the 750 headset, without the boom microphone.

2.2 Models covered

Model Number Description Connector
Airman 750
64300-200 Double	side headset, 2x PJ, 150 Ω PJ-068/PJ-055 (or equivalent)
64300-205 Double	side headset, 2x A5M, 150 Ω XLR 5-pin Male
64300-208 Double	side headset, 2x A5M, 150 Ω, 7ft	XLR 5-pin Male
64300-210 Double	side headset, 2x A5M, 600 Ω XLR 5-pin Male
64300-212 Double	side headset, 2x PJ, 600 Ω PJ-068/PJ-055 (or equivalent)
64300-218 Double	side headset, 2x PJ, 150 Ω, 8ft PJ-068 (or equivalent)
64300-219 Double	side headset, 2x A4F, 150 Ω XLR 4-pin Female
64300-220 Double	side headset, 2x PJ, 150 Ω PJ-068/PJ-055 (or equivalent)
64300-2300 Single	side headset, 2x PJ, 300 Ω PJ-068/PJ-055 (or equivalent)
Airman 760
644-200 Double side	headphone, PJ, 150 Ω PJ-055 (or equivalent)

Table 2.1: Airman 750/760 Models and Connector

Notice!

Model 644-000, -203 and Models 64300-00, -005, -105, -008, -108, -010, -110, -012, -112, -016, -116, -018, -118, -019, -119, -020, -021, -121, -022, -122, -201, -216 are no longer supported and are not covered in this CMM.

2.3 Specifications

Receivers

Type: Dynamic

Impedance: 150

64300-200, -205, -208, -218, -219, -220;

64400-200

300 Ω

64300-300

600 Ω

64300-210,-212

Frequency response: 100 Hz to 3000 Hz

Sensitivity: 90 dB SPL ±5 dB at 1 kHz, 1 mW input

Microphone (Airman 750 only)

Type: Noise-canceling amplified electret

Matching impedance: 50 to 600 Ω

Frequency response (Airman 750): 300 Hz to 5000 Hz within limits shown below

Sensitivity: Ref. 1 V/μbar @1 kHz, 12 VDC

- 51 +3/-3 dB (all versions except -220)

-44+2/-1dB(-220)

Total Harmonic Distortion (THD): Less than 5% from 350 Hz to 6000 Hz when the microphone is exposed to 114 dB SPL input.

Operating voltage: 8 to 16 VDC (470 Ohm load)

MICROPHONE FREQUENCY RESPONSE
Figure 2.1: Microphone Frequency Response

Approximate gross weight

	Airman 750 Airman 760
Single-sided 4 oz. (113 g) 3 oz.	(85 g)
Double-sided	4.8 oz. (136 g)

Approximate wearing weight

	Airman 750 Airman 760
Single-sided 2.3 oz. (65 g) 2.2	oz. (62 g)
Double-sided 3.2 oz. (91 g)

Plug type

Varies by model. Refer to Models covered, page 7.

Cord length

Varies by model. Refer to Disassembly and assembly, page 14.

3 Parts list

3.1 General

When replacing parts, consult the illustration, Airman 760, catalog number 64400-200, page 10 and Airman 750, catalog number 64300-200, -205, -208, -210, -212,-218, -219, -220, and -300, page 11. Choose the parts corresponding to the catalog/model.

Figure 3.1: Airman 750/760 series-200/300 exploded view

3.2 Airman 760, catalog number 64400-200

Item Ordering Part Number Description Model			-200
1 59040	4360 SCRW PT, PAN HEAD, K15 X 6MM, BLK ZINC 4
2 59040	2002 EAR CUSHION (1 per pkg.) 2
	800456055OR64301000	EAR CUSHION (2 per pkg.) 1
3 70133	35000 CUSHION PAD 2
4 63988	8002 CORD	LENGTH: 5.5 ± 0.2 ft. ( 1.68 ± 0.15 m)	1
5 590637000 CLOTHING CLIP 1
8 64308100 HOUSING (Receiver) ASSY PACKAGED, left side 1
9 64308110 HOUSING (Receiver) ASSY PACKAGED, right 1
10 64404018 HOUSING REAR, right side no printing 1
11 S-64318081 HEADBAND ASSEMBLY 1
12 64310000 GLIDER ASSEMBLY 2
13 64330500 GLIDER SPRING
14 Not Available as a replaceable part		CIRCUIT BOARD	1
15 F01U327242 HOUSING REAR, LEFT SIDE 1

3.3

Airman 750, catalog number 64300-200, -205, -208, -210, -212, -218, -219, -220, and -300

Item	Ordering Part Number	Description	Models
			200	205	208	210	212	218	219	220	300
1	590404360	SCREW, PT, PAN HEAD, K15 X 6MM, BLK ZINC	4	4	4	4	4	4	4	4	2
2	590402002	EAR CUSHION (1 per pkg.)	2	2	2	2	2	2	2	2	1
	8004560005OR64301000	EAR CUSHION (2 per pkg.)	1	1	1	1	1	1	1	1
3	701335000	CUSHION PAD	2	2	2	2	2	2	2	2	1
4	70113002	CORDApproximate Length:5.5 ft. (1.67 m)	1								1
	63988018	CORDApproximate Length:5.8 ft. (1.76 m)		1
Item	Ordering Part Number	Description Models
	63988025 C	ORD Approximate Length: 7 ft. (2.13 m)			1
	63988031 C	ORD Approximate Length: 6 ft. (1.82 m)				1
	70413002 C	ORD Approximate Length: 5.5 ft. (1.67 m)					1
	63988043 C	ORD Approximate Length: 8 ft. (2.4 m)						1
	S-F01U327247	CORD 1
	70413006 C	ORD Approximate Length: 5.5 ft. (1.67 m)								1
5 590	637000	CLOTHING CLIP 1 1 2 1 1 1 1 1 1 1
8 643	08100 HOUS	ING (Receiver) ASSY PACKAGED, left side		1 1 1
	64308108 H	OUSING (Receiver) ASSY PACKAGED, left side				1
	64308115 H	OUSING (Receiver) ASSY PACKAGED, left side	1 1 1 1
	64308117 H	OUSING (Receiver) ASSY PACKAGED, left side					1
9 643	08110 HOUS	ING (Receiver) ASSY PACKAGED, right side	1 1 1 1 1 1 1 1
10 64	404018 HOUS	SING REAR, right side 1 1 1 1	1 1 1 1
	ESP-F01U323856	HOUSING REAR, right side (printed)
11 64	318069 HEAD	DBAND ASSEMBLY 1
	64318070 H	EADBAND ASSEMBLY 1
	63993010 H	EADBAND ASSEMBLY 1
	64318071 H	EADBAND ASSEMBLY			1
	S064318071	HEADBAND ASSEMBLY 1
	64318074 H	HEADBAND ASSEMBLY 1
	S-F01U327241	HEADBAND ASSEMBLY 1
	S-64318075	HEADBAND ASSEMBLY 1
	64318085 H	HEADBAND ASSEMBLY 1
12 64	310000 GLIDER ASSEMBLY 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 1
13 64	305000 GLIDER SPRING 1-piece 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 3
	S-F01U327240	GLIDER SPRING 10-piece
14 60	0578000	PCBA 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 3
15 64	307008 BOOM ASSEMBLY 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 2
	64307013 BOOM ASSEMBLY 1					1	1		1	1
16 59	688000 WINDSCREEN 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 4
	800456001	WINDSCREEN + O-RING	1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
17^a	580001003	OPTIONAL O-RING	1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
18 70	531004 TEMPLE PLATE									1
20 70	533000 TEMPLE PLATE FOAM PAD									1
21^b	701246000	BOOM ROTATOR CAP	1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 3
22 S-F01U322242	OVERHEAD CORD		1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 4

^a Windscreen (59688000) is standard equipment. Optionally, windscreen + o-ring (800456001) can be used.

^b Not shown. Included as part of item 15 (Boom Assembly) or can be purchased separately.

4 Disassembly and assembly

The following procedure allows for complete disassembly of the Airman 750 and Airman 760. Refer to the illustration and to Parts list, page 10.

Figure 4.1: Airman 750/760 series-200/300 exploded view

Notice!

Assembly is the reversal of the disassembly procedure. Please take care when disassembling to note details that may be required in the assembly process, such as the locations of disconnected wires.

When soldering, be careful not to touch the plastic housing of the headset/headphone with the soldering iron.

4.1 Disassembly

4.1.1 Removal of the receiver assembly

To remove the receiver assembly, do the following:

1. Gently remove the foam ear cushion (2) (and ear cushion pad if present).

2. Using a Torx-5 screwdriver, remove the two screws (1) from the receiver assembly (8, 9).

The rear housing separates from the receiver assembly and the headband.

Notice!

Do not pull the receiver assembly more than 12 mm away from the rear housing at this time.

1. For the cord side, using a soldering iron, carefully disconnect the red and white internal wires from either the circuit board or the receiver assembly.

OR

For the non-cord side, continue to the next step.

1. Using a soldering iron, carefully disconnect the overhead cord wires from the receiver assembly.

Figure 4.2: Circuit board / Receiver / Cord Wiring

Notice!

Airman 750 model -300 does not have overhead cord wires.

4.1.2 Removal of the cord assembly

To remove the cord assembly, do the following:

1. Gently remove the foam ear cushion (2) (and ear cushion pad if present).
2. Using a Torx-5 screwdriver, remove the two screws (1) from the receiver assembly (8, 9). The rear housing separates from the receiver assembly and the headband.

Notice!

Do not pull the receiver assembly more than 12 mm away from the rear housing at this time.

1. For the cord side, using a soldering iron, carefully disconnect the red and white internal wires from either the circuit board or the receiver assembly.

OR

For the non-cord side, continue to the next step.

1. Using a soldering iron, on the circuit board carefully disconnect the four wires from the cord assembly (4).

4.1.3 Removal of the circuit board and boom assembly (Airman 750)

To remove the circuit board, do the following:

1. Follow steps 1 to 2 in the procedure for removing the cord assembly. Refer to Removal of the cord assembly, page 15.

2. If disassembling an Airman 750, use a soldering iron on the circuit board to carefully disconnect the two boom wires from J10 and J11.

OR

If disassembling an Airman 760, continue to next step.

1. Pull back the black clasps on the side of the circuit board to release it for removal. The 750 boom assembly is now free of all headset components.

Notice!

Appearances vary slightly for some versions. Refer to Parts list, page 10 for part number descriptions and ordering number.

4.1.4 Removal of a glider

To remove a glider from the headset, do the following:

1. Using a pair of needle nose pliers, straighten the crimp at the end of the glider.
2. Once the crimp is straightened, gently slide the slider through the glider stabilizer.

Notice!

Take care not to lose the glider spring (a small curved rectangular piece of plastic). The glider spring provides tension to hold the glider in place when mounted in the headset. The outward facing arc should be touching the glider providing some tension.

1. Repeat steps 1 and 2 for dual-sided headset models.

For a complete list of wiring diagram information, refer to Wiring and connectors, page 17.

4.2 Assembly

Notice!

Assembly is a reversal of the disassembly procedure. Steps need to be done exactly the reverse order of the disassembly procedure to ensure proper headset fit and operation. Please take care to properly align parts and wires to ensure proper operation. See disassembly procedure, parts lists, assembly diagrams, and wiring diagrams for reference.

Notice!

Speaker wires and overhead cord must be routed around the perimeter of the magnet in the receiver assembly to ensure they do not get pinched between the circuit board and the speaker.

5 Wiring and connectors

5.1 Airman 750 wiring diagrams

Notice!

On the speaker, the positive terminal is usually indicated with a dot.

5.1.1 Catalog numbers 64300 -200, -220, -300

Notice!

With model -300 omit overhead cordage.

Figure 5.1: Airman 750 Headset Model -200, -220, -300 Wiring Diagram

5.1.2 Catalog number 64300 -210

Figure 5.2: Airman 750 Headset Model -210 Wiring Diagram

5.1.3 Catalog numbers 64300 -205, -208

Figure 5.3: Airman 750 Headset Model -205, -208 Wiring Diagram

5.1.4 Catalog number 64300 -212

Figure 5.4: Airman 750 Headset Model -212 Wiring Diagram

5.1.5 Catalog number 64300 -218

Figure 5.5: Airman 750 Headset Model -218 Wiring Diagram

5.1.6 Catalog number 64300 -219

Figure 5.6: Airman 750 Headset Model -219 Wiring Diagram

5.2 Airman 760 wiring diagrams

5.2.1 Catalog number 64300 -200

Figure 5.7: Airman 760 Headphone Model -200 Wiring Diagram

5.3 Airman 750 connectors

5.3.1 Connector view for catalog numbers 64300-200, -212, -300

Microphone: .206 in (5.2 mm) DIA.

Receiver: .250 in (6.4 mm) DIA.

Two types of electrical connectors with internal circuitry, no text or symbols present

Figure 5.8: PJ068 and PJ055 Connector, 750 Model -200, -212, -300

Figure 5.9: PJ068 and PJ055 Connector Wiring, 750 Model -200, -212, -300

5.3.2 Connector view for catalog numbers 64300-205, -208, -210

XLR connector: Neutrik 5MC or equivalent

Simple line drawing of a screwdriver with a handle and pointed tip (no text or symbols)

Figure 5.10: XLR Connector, 750 Model -205, -208, -210

Figure 5.11: XLR Connector Wiring, 750 Model -205, -208, -210

5.3.3 Connector view for catalog number 64300-218

PJ-068: .206 in (5.2 mm) DIA.

Pure electrical circuit lines without any symbols

Figure 5.12: PJ-068 Connector, 750 Model -218

Figure 5.13: PJ-068 Connector Wiring, 750 Model -218

5.3.4 Connector wiring diagram for catalog number 64300-219

XLR connector: Neutrik NC4FX or equivalent

Simple line drawing of a tool handle (no text or symbols)

Figure 5.14: XLR Connector, 750 Model -219

Figure 5.15: XLR Connector Wiring, 750 Model -219

5.3.5 Connector wiring diagram for catalog number 64300-220

Microphone: .206 in (5.2 mm) DIA. right angle

Receiver: .250 in (6.4 mm) DIA. right angle

Pure electrical connector diagram without any text, numbers, or symbols

Figure 5.16: PJ068 and PJ055 Connector, 750 Model -220

Figure 5.17: PJ055 and PJ068 Connector Wiring, 750 Model -220

5.4 Airman 760 connectors

5.4.1 Connector view for catalog number 64400-200

PJ-055: .25 in (6.4 mm) DIA.

Pure electrical circuit lines without any symbols

Figure 5.18: PJ-055 Connector, 460 Model -200

Figure 5.19: PJ-055 Connector Wiring, 760 Model -200

6 Maintenance

6.1 Microphone validation and adjustment

6.1.1 Microphone and amplifier sensitivity check

Headset specifications are designed to comply with FAA TSO C-57a, C-58a, including RCTA DO-170 and DO-160D.

To test the sensitivity of the microphone, do the following:

1. Construct a test circuit. For more information, see Figure 1.
2. Connect the test circuit to the microphone plug of the headset. For more information, refer to Models covered, page 7.

Figure 6.1: Airman 750 Headset Boom Microphone Sensitivity Check Test Circuit

1. Calibrate a lab microphone.
2. Place the calibrated lab microphone 1/4 inch (6 mm) above an artificial mouth (Bruel and Kjaer type 4219).
3. Connect a signal generator to the artificial mouth.
4. Adjust for an output of 100 dBspl or of 114 dBspl @ 1/4 inch from the opening to the lab microphone.
5. Remove the lab microphone.
6. Position the headset boom microphone 1/4 inch (6 mm) above the output of the artificial mouth.

Notice!

The acoustic hole in the boom mic should be aligned with the center of the artificial mouth opening. Windscreens should be removed for this test.

1. Measure the output of the headset microphone with a digital voltmeter.

Artificial mouth output Microphone sensitivity specification

All versions except -220: @100 dB	63 mVrms +16/-7 mVrms
@114 dB	316 mVrms +82/-34 mVrms
For -220 use: @100 dB	126 mVrms +33/-14 mVrms
@114 dB	631 mVrms +163/-169 mVrms

Table 6.2: Microphone sensitivity specifications

6.1.2 Microphone sensitivity adjustment

Microphone sensitivity is adjusted by turning the gain adjustment control, using a small screwdriver through the opening in the left outer housing assembly. The screwdriver connects with the gain adjustment potentiometer (R11) on the circuit board. Clockwise adjustment increases output level.

Technical line drawing of a mechanical component with a tool and circular feature (no text or symbols)

Figure 6.2: Gain Adjustment Control

For Internal Reference Only

Figure 6.3: Gain Adjustment Potentiometer (R11)

Final sensitivity at 1 kHz shall be set with gain adjust potentiometer R11. Refer to Microphone and amplifier sensitivity check, page 24.

6.1.3 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.

6.2 Circuit board - 200/300 Series Airman 750

The same circuit board is used in all 200 and 300 Series versions of the Airman 750 Headset. Circuit boards may be tested while outside of the headset chassis using the following test circuit:

1. Specifications apply with SW1 in both normal and reverse positions.
   Specifications
2. Vin = 0.47mVAC, 1000 Hz
3. lx = 17 ± 2mA
4. Vout = 297 - 592 mV

When pot is set to midpoint.

Figure 6.4: Test circuit for Airman 750

6.2.1 Testing the circuit board assembly

To test the circuit board assembly, do the following:

1. Construct the test circuit.
2. Connect the circuit board to the test circuit.
3. Remove the circuit board and wiring completely from the headset.
4. Set Vin to measure 0.47 mVAC, 1Khz, VOUT should read 297-592 mV, when pot is set to midpoint.

If the output is outside this range, replace the circuit board. Specifications apply with SW1 in both normal and reverse positions.

6.3 Speaker validation

6.3.1 Speaker sensitivity and frequency response verification

Transducer type Dynamic

Sensitivity (All Models) 104 dB SPL ±5 dB at 1 kHz, 1 mW

input to headset, at LOW volume control setting. 1 mW based on input impedance of headset being tested.

Frequency response Must meet standards outlined in the

specifications.

Earphone testing for the Airman 750 and 760 is done on a flat plate coupler.

To measure the speaker, do the following:

1. Calibrate a lab microphone.

2. Connect an audio analyzer to the lab microphone.

3. Place the calibrated lab microphone under the flat plate coupler and up through the hole, flush to the microphone positioning flange.

Figure 6.5: Flat Plate Coupler

1. Place the speaker (without the foam ear cushion or pad) flush to the top of the flat plate coupler, centered over the hole.
2. Use a constant voltage sine wave generator with a 50 Ω output impedance to supply the speaker with a 1 mW, 1 KHz signal to the appropriate connector. For more information, refer to Models covered, page 7.
   

Notice!

Once the headset/headphone is connected to the constant voltage sine wave generator, the output voltage can be measured at the sine wave generator or by the audio analyzer connected to the lab microphone.
6. Adjust the voltage across the headset per the following table.

VERSION VOLTAGE AC	ROSS HEADSET PLUG	SPEAKER WIRING IMPEDANCE
64300-200, -205,-208,-218, -219, -22064400-200	.39 VRMS Parallel 150 Ω
64300-300 .39 VRMS Stereo 300 Ω
64300-210, -212 .77 VRMS Series 600 Ω

Table 6.3: Headset/headphone voltage, speaker wiring, and impedance

1. Measure the acoustic output of the headset, using the audio analyzer OR the constant voltage sine wave generator.

Notice!

Earphone sensitivity @1 kHz should be 104 ±5 dB on the earphone.

1. Measure and record the acoustic output over the frequency range of 350 Hz to 3 KHz.

Notice!

The resultant curve should fit the limits as defined in Description and specifications, page 7.

1. Repeat steps 1 through 8 with the second speaker, if applicable.

7 Troubleshooting

7.1 Troubleshooting chart

	Check plug(s)	Check amplifier	Check cord	Check boom mic assembly and internal wiring	Check speaker(s) and internal wiring	Check amplifier gain adjust
Receiver inoperative	X X X
Microphone inoperative	X X X X
Receiver intermittent	X X X
Microphone intermittent	X X X X
Distorted receiver signal					X
Distorted microphone signal		X X X
Microphone level cannot be adjusted properly		X X X

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