23413500

23-41-35

COMPONENT MAINTENANCEMANUAL with IPLHMEC 25-KAXPART NO 025-230-415

componentmaintenance manual

(with illustrated parts list)

Sennheiser electronic GmbH & Co. KGD - 30900 WedemarkTel.: 05130 / 600 - 0

Fax: 05130 / 600 - 300Vendor Code: D 8114

Printed in Germany

June 29/98

• 75532

This manual includes coverage of the following equipment:

Model No Sennheiser Part No

Boomset HMEC 25-KAX 025-230-415

HMEC 25

23-41-35


Record of RevisionsPages 1/2

June 29/98

RECORD OF REVISIONS

REVNO

ISSUEDATE

DATEINSERTED BY REV

NOISSUEDATE

DATEINSERTED BYREV

NOISSUEDATE

DATEINSERTED BY

23-41-35


Record of Temporary RevisionsPages 1/2

June 29/98

RECORD OF TEMPORARY REVISIONS

BYBYISSUEDATE

PAGENUMBER

DATEREMOVED

TEMPORARYREV NO

23-41-35


Service Bulletin ListPages 1/2

June 29/98

SERVICE BULLETIN LIST

SERVICEBULLETIN

NO

MANUALREVISION

DATE

MANUALREVISIONNUMBER

SUBJECT

NOTE: Refer to modification history figure preceding schematic diagrams for additional servicebulletin information

23-41-35


LIST OF EFFECTIVE PAGES

SUBJECT PAGE DATE

Title June 29/98

Record of 1 June 29/98Revisions 2 Blank

Record of 1 June 29/98Temporary 2 BlankRevisions

Service Bulletin 1 June 29/98List 2 Blank

List of Effective 1 June 29/98Pages 2 Blank

Table of 1 June 29/98Contents 2 June 29/98

Introduction 1 June 29/982 June 29/983 June 29/984 June 29/98

Description 1 June 29/98and Operation 2 June 29/98

3 June 29/984 June 29/985 June 29/986 Blank

Testing and 101 June 29/98Troubleshooting 102 June 29/98

103 June 29/98104 June 29/98105 June 29/98106 June 29/98107 June 29/98108 June 29/98109 June 29/98110 June 29/98111 June 29/98112 June 29/98

SUBJECT PAGE DATE

Disassembly 301 June 29/98302 June 29/98303 June 29/98304 Blank

Cleaning 401 June 29/98402 Blank

Check 501 June 29/98502 Blank

Repair 601 June 29/98602 Blank

Assembly 701 June 29/98(Including 702 June 29/98Storage) 703 June 29/98

704 June 29/98

Fits and 801 June 29/98Clearances 802 Blank

Special Tools, 901 June 29/98Fixtures, and 902 June 29/98Equipment 903 June 29/98

904 June 29/98

Illustrated Parts 1001 June 29/98List 1002 June 29/98

1003 June 29/981004 June 29/981005 June 29/981006 Blank

List of Effective PagesPages 1/2

June 29/98

* The asterisk indicates pages changed, added, or deleted by the current change.

23-41-35


TABLE OF CONTENTS

SUBJECT PAGE

INTRODUCTION.......................................................................................................................... 1

1. General ....................................................................................................................... 12. List of Illustrations ........................................................................................................ 23. Advisories ................................................................................................................... 34. Frontispiece................................................................................................................. 4

DESCRIPTION AND OPERATION................................................................................................... 1

1. General ....................................................................................................................... 12. Purpose of Equipment .................................................................................................. 13. Equipment Specifications .............................................................................................. 24. Equipment Description.................................................................................................. 3

A. Mechanical Description ....................................................................................... 3B. Electrical Description .......................................................................................... 5

TESTING ............................................................................................................................... 101

1. Testing .................................................................................................................... 101A. Introduction ................................................................................................... 101B. Test Equipment and Power Requirements ........................................................ 101C. Test Procedures ............................................................................................ 101

2. Troubleshooting ....................................................................................................... 103A. Philosophy ..................................................................................................... 103B. Troubleshooting Approach .............................................................................. 103C. Troubleshooting Aids ...................................................................................... 104D. NoiseGard® active noise compensation ............................................................ 104E. Introduction to HMEC 25 Troubleshooting ........................................................ 105

DISASSEMBLY ....................................................................................................................... 301

1. Introduction ............................................................................................................. 3012. Precautions and General Techniques ......................................................................... 3013. Procedure ............................................................................................................... 301

A. Ear pad Disassembly ...................................................................................... 302B. Headphone Capsule Disassembly .................................................................... 302C. Microphone Arm Holder Disassembly ............................................................... 303

CLEANING ............................................................................................................................. 401

1. Introduction ............................................................................................................. 4012. Cleaning Materials .................................................................................................... 4013. Procedures .............................................................................................................. 401

Table of ContentsPage 1

June 29/98


23-41-35

TABLE OF CONTENTS

SUBJECT PAGE

CHECK .................................................................................................................................. 501

1. Introduction ............................................................................................................. 5012. Procedures.............................................................................................................. 501

REPAIR .................................................................................................................................. 601

1. Introduction ............................................................................................................. 6012. Repair Supplies ........................................................................................................ 6013. Procedures.............................................................................................................. 601

ASSEMBLY ............................................................................................................................ 701

1. General ................................................................................................................... 7012. Precautions and General Techniques ......................................................................... 701

A. Wiring ............................................................................................................ 7013. Detailed Assembly Procedures .................................................................................. 701

A. Microphone Arm Holder Assembly ................................................................... 702B. Headphone Capsule Assembly ........................................................................ 703C. Ear Pad Assembly .......................................................................................... 703

4. Final Testing ............................................................................................................ 7045. Storage Instructions ................................................................................................. 704

FITS AND CLEARANCES ......................................................................................................... 801

SPECIAL TOOLS, FIXTURES, AND EQUIPMENT ......................................................................... 901

1. Test Equipment/Resource Requirements ................................................................... 901

ILLUSTRATED PARTS LIST .................................................................................................... 1001

1. Introduction ........................................................................................................... 1001A. Detailed Parts List ........................................................................................ 1001

Table of ContentsPage 2

June 29/98

23-41-35


INTRODUCTION

1. General

This component maintenance manual (with illustrated parts list) includes maintenance instructions preparedin accordance with ATA Specification No 100 for Manufacturers’ Technical Data for the SennheiserHMEC 25 Boomset.

REMARK: TESTING AND SERVICING HEADPHONE AND MICROPHONE SECTION IS HANDLED IN TWOSEPARATE MANUALS. WITH THE NEW VERSION OF THE HMEC 25 BOOMSET THEMICROPHONE AMPLIFIER IS LOCATED IN THE HOUSING OF THE NEW MKE 45 ELECTRETMICROPHONE. THIS MODULAR DESIGN OF ELECTRET MICROPHONE CAPSULE ANDMICROPHONE AMPLIFIER FITTED TOGETHER IN A STAND-ALONE HOUSING SEPARATE FROMTHE HEADPHONE SECTION PROVIDES A HIGHER FLEXIBILITY TOWARDS NEW PRODUCTS,SO THAT ALL NEW HEADSETS FOR AVIATION (E.G. HMEC 25, HME 45 AND HMEC 45) AREEQUIPPED LIKEWISE.

The maintenance instructions are presented in the following sections: Description and Operation; Testing;Disassembly; Cleaning; Check; Repair; Assembly (Including Storage); Fits and Clearances; Special Tools,Fixtures, and Equipment; and Illustrated Parts List.

This component maintenance manual provides shop-verified procedures that will enable a mechanicunfamiliar with the equipment to restore it to a serviceable condition. The procedures are prepared for themechanic that performs shop work and not for the aircraft mechanic.

CAUTION: THE MATERIAL IN THIS MANUAL IS SUBJECT TO CHANGE. BEFORE ATTEMPTING ANYMAINTENANCE OPERATION ON THE EQUIPMENT COVERED IN THIS MANUAL, VERIFY THATYOU HAVE COMPLETE AND UP-TO-DATE PUBLICATIONS BY REFERRING TO THE APPLICABLEPUBLICATIONS AND SERVICE BULLETIN INDEXES.

We welcome your comments concerning this manual. Although every effort has been made to keep it freefrom errors, some may occur. When reporting a specific problem, please describe it briefly and includethe manual part number, the paragraph or figure number, and the page number.

Send your comments to: Sennheiser electronic GmbH & Co. KGPublications DepartmentD - 30900 Wedemark

IntroductionPage 1

June 29/98


23-41-35

2. List of Illustrations

FIGURE PAGE

1 Equipment Covered ....................................................................................................... 12 Equipment Specifications ............................................................................................... 23 HMEC 25-KAX Outline Dimensions .................................................................................. 34 HMEC 25-KAX Connector Pin Assignments ...................................................................... 4

101 Test Setup Diagram 1 ............................................................................................... 102102 Test Procedures ....................................................................................................... 102103 Test Procedure Outline .............................................................................................. 105104 Test Setup Diagram 2 ............................................................................................... 106105 Fault Isolation Procedure ........................................................................................... 106106 Test Setup Diagram 3 ............................................................................................... 107107 HMEC 25 NoiseGard® Circuit Card Assembly, Maintenance Aid Diagram ....................... 108108 HMEC 25 NoiseGard® Circuit Card Assembly, Schematic Diagram ................................ 109109 HMEC 25-KAX Schematic Diagram ............................................................................. 110110 HMEC 25 Wiring Diagram .......................................................................................... 111111 HMEC 25-KAX Connecting Cable ................................................................................ 112

301 HMEC 25 Ear Pad Disassembly .................................................................................. 302302 HMEC 25 Headphone Capsule Disassembly ................................................................ 302303 HMEC 25 Microphone Arm Holder Disassembly ........................................................... 303

401 Cleaning Materials ..................................................................................................... 401

701 HMEC 25 Microphone Arm Holder Assembly ............................................................... 702702 HMEC 25 Headphone Capsule Assembly ..................................................................... 703703 HMEC 25 Ear Pad Assembly ...................................................................................... 703

901 Tools, Fixtures, and Equipment .................................................................................. 901

1 HMEC 25-KAX Boomset Assembly ............................................................................ 10022 HMEC 25 Microphone Arm Holder Assembly ............................................................. 1004

IntroductionPage 2

June 29/98

23-41-35


IntroductionPage 3

June 29/98

3. Advisories

WARNING: THIS UNIT EXHIBITS A VERY HIGH DEGREE OF FUNCTIONAL INTEGRITY. NEVERTHELESS,USERS MUST RECOGNIZE THAT IT IS NOT PRACTICAL TO PROVIDE MONITORING FOR ALL CONCEIVABLESYSTEM FAILURES AND THAT, HOWEVER UNLIKELY, IT IS POSSIBLE THAT ERRONEOUS OPERATIONCOULD OCCUR WITHOUT A FAULT INDICATION. THE PILOT HAS THE RESPONSIBILITY TO DETECT SUCHAN OCCURRENCE BY MEANS OF CROSS-CHECKS WITH REDUNDANT OR CORRELATED INFORMATIONAVAILABLE IN THE COCKPIT.

WARNING: WHILE PERFORMING MAINTENANCE WITH THE COVERS REMOVED FROM THIS UNIT, SERVICEPERSONNEL ARE ADVISED TO OBSERVE STANDARD SAFETY PRECAUTIONS TO PREVENT PERSONALINJURY.

CAUTION:

ESDS DEVICES ARE SUBJECT TO DAMAGE BY EXCESSIVE LEVELS OF VOLTAGE AND/OR CURRENT, JUSTAS ARE MORE CONVENTIONAL SEMICONDUCTOR DEVICES. HOWEVER, THE PRECAUTIONS NORMALLYUSED TO PROTECT SEMICONDUCTORS ARE NOT SUFFICIENT FOR THE PROTECTION OF ESDSCOMPONENTS, BECAUSE OF THEIR VERY HIGH ELECTRICAL RESISTANCE. THE LOW-ENERGY SOURCETHAT MOST COMMONLY DESTROYS ESDS DEVICES IS THE HUMAN BODY, WHICH IN CONJUNCTION WITHNONCONDUCTIVE GARMENTS AND FLOOR COVERINGS GENERATES AND RETAINS STATIC ELECTRICITY.

IN ORDER TO ADEQUATELY PROTECT ESDS DEVICES, THE DEVICE AND EVERYTHING THAT CONTACTS ITMUST BE BROUGHT TO GROUND POTENTIAL BY PROVIDING A CONDUCTIVE SURFACE AND DISCHARGEPATHS. THE FOLLOWING PRECAUTIONS MUST BE FOLLOWED:

A. DEENERGIZE OR DISCONNECT ALL POWER AND SIGNAL SOURCES AND LOADS.

B. PLACE THE UNIT ON GROUNDED CONDUCTIVE WORK SURFACE.

C. GROUND THE REPAIR OPERATOR THROUGH A CONDUCTIVE WRIST STRAP OR OTHER DEVICE USING A470-kΩ OR 1-MΩ SERIES RESISTOR TO PROTECT THE OPERATOR.

D. GROUND ANY TOOLS, SUCH AS SOLDERING EQUIPMENT, THAT WILL CONTACT THE UNIT. CONTACTWITH THE OPERATOR’S HAND PROVIDES A SUFFICIENT GROUND FOR TOOLS THAT ARE OTHERWISEELECTRICALLY ISOLATED.

E. WHEN ESDS DEVICES AND ASSEMBLIES ARE NOT IN THE UNIT, THEY SHOULD BE ON THECONDUCTIVE WORK SURFACE OR IN CONDUCTIVE CONTAINERS. WHEN A DEVICE OR ASSEMBLY ISINSERTED IN OR REMOVED FROM A CONTAINER, THE OPERATOR SHOULD MAINTAIN CONTACT WITHTHE CONDUCTIVE PORTION OF THE CONTAINER. DO NOT USE PLASTIC BAGS UNLESS THEY HAVEBEEN IMPREGNATED WITH A CONDUCTIVE MATERIAL.

F. DO NOT HANDLE ESDS DEVICES UNNECESSARILY OR REMOVE THEM FROM THEIR PACKAGES UNTILACTUALLY USED OR TESTED.

G. TO PREVENT DAMAGE BY TRANSIENT VOLTAGES, ONLY SOLDERING IRONS HAVING ZERO VOLTAGEAT THE TIP SHOULD BE USED.

CAU

TIO

N CAU

TION

ELECTROSTATICSENSITIVE DEVICES

OBSERVE PRECAUTIONSFOR HANDLING


23-41-35Introduction

Page 4June 29/98

4. Frontispiece

Typical HMEC 25 Boomset

23-41-35


Page 1June 29/98

DESCRIPTION AND OPERATION

1. General

Refer to frontispiece for an overall view of the HMEC 25 Boomset. Figure 1 is a list of the equipmentcovered in this manual.

MODEL NO DESCRIPTION SENNHEISERPART NUMBER

HMEC 25-KAX Boomset with microphone amplifier and 025-230-415jack connector. Microphone amplifier isfitted in the microphone housing. The Boomsetfacilitates +12 to 35 V Jack Panel powering using aspecially designed XLR connectorwith a DC/DC Converter.

Equipment CoveredFigure 1

2. Purpose of Equipment

The HMEC 25 Boomset was designed to provide excellent wearing comfort by making it lightweight,provide unequaled transmission quality by using Sennheiser´s own noise-compensated microphones andacoustically matched earphone transducers.

The HMEC 25 Boomset is designed to permit permanent use in aircraft cockpits. It incorporateselectronic circuits and components that serve to process signals for a Standard Jack Panel.

The HMEC 25 Boomset is powered from +16 V dc supplied by a Standard Jack Panel.The NoiseGard® circuit is powered from +12 to 35 V dc supplied by a Jack Panel.


23-41-35

PhysicalWeight, without cable approx. 170 grLength of cable 1.8 m

Panel connector PJ-055 (Headphone), PJ-068 (Microphone)XLR 3-pin plug (Panel powering)

HeadphonesTransducer principle dynamic, supraaural, closedFrequency response 16 to 22,000 HzImpedance 200 Ω (connected in parallel)Sensitivity (1 kHz, 1 mW) 92 dB/SPL ± 3 dBActive noise compensation ≥ 15 dB ± 1.5 dB between 100 Hz and 2 kHzTotal harmonic distortion < 1 %Headband pressure approx. 2.5 N

Microphone and amplifier*Transducer principle back-electret condenser capsule, noise-compensatedFrequency response 300 to 5,000 HzMax. sound pressure level 120 dB(distortion < 5 %)Output voltage 400 mV ± 3 dB at 114 dB/SPL

(corresponding to RTCA/DO 214)Terminating impedance 150 ΩSupply voltage typ. 16 V dc (8 V to 16 V), approx. 20 mAPower supply for NoiseGard® system +12 to 35 V dc Jack Panel supply fed into XLR 3-pin plug.

Typical current consumption between 10 mA and 30 mAwith a maximum of 50 mA

3. Equipment Specifications

Figure 2 lists the specifications for the HMEC 25-KAX Boomset.

CHARACTERISTICS SPECIFICATION

Page 2June 29/98

Equipment SpecificationsFigure 2

*NOTE: For servicing the MKE 45 microphone refer to the CMM MKE 45, Part No. 70566, ATARF 23-41-24.

23-41-35


4. Equipment Description

A. Mechanical Description

The HMEC 25-KAX Boomset is connected to a Standard Jack Panel with two jack plugs. The boomsetconsists of a split headband and two headphone systems. The boom microphone can be rotated throughapprox. ±135°.

Page 3June 29/98

HMEC 25-KAX Outline DimensionsFigure 3


23-41-35

B. Electrical Description

The MKE 45 microphone of the HMEC 25-KAX Boomset is powered from + 16 V dc. The boomset consistsof a boom microphone with amplifier for air traffic communication and two headphone systems.

Page 4June 29/98

PIN / CONDUCTOR FUNCTION

1 / red Boom microphone Hi2,4 / blue,screen Boom microphone Lo3 / blue Ground (Supply voltage)5 / red +12 V Supply voltage6 / black Audio sidetone Lo7,8 / yellow,blue Audio sidetone Hi

HMEC 25-KAX Connector Pin AssignmentsFigure 4

Front view

Input +12 to 35 V Ground

5

3

23-41-35


TESTING AND TROUBLESHOOTING

1. Testing

A. Introduction

Avionics equipment requiring testing usually falls into the following categories:

(1) Units received from the line maintenance personnel with a general complaint of bad or no function thatrequire testing to verify that a fault exists.

(2) Units that have been repaired and must be verified by the repairing agency as a part of the repaircycle.

WARNING: WHILE PERFORMING MAINTENANCE WITH THE COVERS REMOVED FROM THIS UNIT, ALLSERVICE PERSONNEL IS ADVISED TO OBSERVE STANDARD SAFETY PRECAUTIONS TOPREVENT PERSONAL INJURY.

The testing information included covers the headphone and NoiseGard® section and is provided to assistthe technician in accomplishing the above two categories.For testing the microphone section (Electret capsule and amplifier) refer to the Component MaintenanceManual for the MKE 45 microphone, Part No. 70566, ATARF 23-41-24.

The performance test provides a functional operational check of the equipment and is recommended to beused as a customer acceptance test if the customer decides to do so. In addition, this test must beperformed on units removed from an aircraft for test or repair prior to reinstallation of that unit.

In the event of a unit from an aircraft is received with a specific complaint, the performance test does nothave to be performed. Saving time rather refer to the test procedure, figure 102, to begin immediatetroubleshooting.

B. Test Equipment and Power Requirements

(1) Test Equipment

Refer to figure 108 and to Tools, Fixtures, and Equipment, figure 901, for test equipment required.

(2) Power Source

The HMEC 25 Boomset requires +16 V dc power for test purposes.The NoiseGard® circuit must be powered by switching on an external +12 to 35 V supply.

C. Test Procedures

Refer to figure 101 for initial setup.

Page 101June 29/98


23-41-35Page 102

June 29/98

SINE - WAVEGENERATOR

Test ProceduresFigure 102

Test Setup Diagram 1Figure 101

IMPEDANCEMETER

Audio frequency signalfrom Jack plug Pin 7,8 to Pin 6

from Jack plug Pin 7,8 to Pin 6

STEP PROCEDURE RESULTS

1.0 HEADPHONE / NoiseGard® CHECK

1.1 Connect Boomset to supply voltage(+12 to 35 V dc).

1.2 Set sine wave generator to 1 kHz/775 mV acand connect as shown in figure 101.Switch off NoiseGard® circuit.

1.3 Vary audio frequency of the sine-wave Aural test of headphonegenerator from 20 Hz to 20 kHz. capsules. Check distortion.

1.4 Disconnect sine-wave generator and check 200 Ωimpedance with impedance meter (1 kHz)

1.5 Disconnect impedance meter and switch onNoiseGard® circuit. Check current consumption. I ≈ (14 - 18) mA

1.6 Put Boomset onto your head. Using your hands No ambient noise like rustle,gently knock against the capsule housing (both humming or hissing must beleft and right). audible. Imax ≈ 50 mA.

1.7 Connect Boomset with sine wave generator and Audio signal must be presentset to 2.2 V rms. Vary audio frequency of the at both left and right channel.sine-wave generator from 20 Hz to 20 kHz. No ambient noise must occur.

23-41-35


Page 103June 29/98

2. Troubleshooting

A. Philosophy

This section is the focal point that repair personnel should use to isolate faults in the unit. All sections ofthis manual contain important information to aid in the accomplishment of total repair and understanding ofthe unit. These sections are referenced, as necessary, to facilitate completion of the repair task.

Troubleshooting avionics equipment usually falls into two categories: failures with a specific complaint andfailures with an unspecified complaint. The function of this section is to guide fault isolation, first to aspecific malfunction, and then to the applicable circuit area. Voltages and waveforms, in addition to thetheory of operation, help lead the technician to isolation of faulty parts.

B. Troubleshooting Approach

(1) Unspecified Complaint

Troubleshooting a unit with an unspecified complaint requires the technician to test the unit according tothe performance test to determine if a fault actually exists.

In cases where the unit passes all portions of the test and no fault is discovered, the unit can be returnedto the aircraft as good and reinstalled.

When a unit does fail the performance test, the next objective is to isolate the actual fault or faults, andbegin in-depth troubleshooting procedures. Begin by performing the specific associated test in the faultisolation test procedure in this section.

(2) Specified Complaint

The test technician may, at his discretion, choose to omit the performance test and proceed directly tothe fault isolation test.

(3) Fault Isolation Test

The next logical step is to perform the specific fault isolation test that is associated with the complaint orfailed step in the performance test. These tests examine more completely the functions and circuitsassociated with the trouble area.

Further testing using the troubleshooting aids provided throughout this manual is necessary to isolateindividual failed parts. These troubleshooting aids are identified and explained in paragraph C.


23-41-35

C. Troubleshooting Aids

(1) Maintenance Aid Diagrams

Maintenance aid diagrams illustrate the physical location of all components on the major assemblies andcan be found adjacent to each applicable schematic diagram.

(2) Test Points

Test points are physical points located on an assembly to allow a technican to make necessary voltageand waveform measurements during fault isolation procedures. These points may or may not be actualjacks.

The test points are identified in a rectangle on the schematic and maintenance aid diagrams. Each testpoint identifies a major voltage or waveform important for circuit operation. These points may also bereferenced in test and troubleshooting procedures.

(3) Waveforms

Waveforms are an important tool in troubleshooting and can be used to fault isolate to a defective stagewhen used properly. Waveforms are located on the maintenance aid diagrams when applicable, and arekeyed to proper test points to aid in their physical location. Near each waveform are listed theoscilloscope settings the technician can use to reconstruct the conditions required to obtain the propermeasurement.

(4) Voltages

Circuit voltages are illustrated on the schematic diagram to help the technician in circuit fault isolation.

D. NoiseGard® active noise compensation

The basic principle of NoiseGard® active noise compensation is built upon the idea of cancelling a definedsignal spectrum of ambient noise disturbing speech related signals. In technical terms this is achieved byadding the ambient noise with the same, but phase-inverted (180°) signal in an electronic circuit. Bothelectret mic capsule, feedback circuitry and headphone capsule represent one complete (and pre-aligned)unit, i.e. due to component tolerances in each unit repairing or exchanging just one unit could lead to anexcessive deviation of bias points towards the compensating parameters. Each such service case meansan elaborated alignment is of high importance involving very specific test procedures and equipment.

For that reason we do not recommend repairing any of these units in separate but preferably exchangingthem as a complete unit! Your stock should be prepared to keep a certain number of complete units asspare in case any malfunction in the compensating circuit is detected. The defective devices then afterexchanging should be sent to the Sennheiser headquarter plant where repair is performed according to allspecifications. Thereafter the devices will be returned to keep your stock complete.

Spare Part No. for ordering a complete unit: – 75550 –

Also refer to page 1002/1003, Detailed Parts List, for an overall - view.

Page 104June 29/98

23-41-35


Page 105June 29/98

(2) Fault Isolation Procedure

The fault isolation procedure (figure 105) is provided as an aid in isolating the cause of failure in aparticular test.

NOTE: The symptoms listed in the fault isolation procedure are those thought to be the most commonand are to help the technican test the circuit in logical sequence. They may not cover all possibleproblems. If a problem is encountered that is not covered in the fault isolation procedure, thewaveforms on the maintenance aid diagrams should be used to isolate a particular problem.

2 NoiseGard® dc voltage Checks internal dc voltages (NoiseGard®) 1.0

3 NoiseGard® signal processing Checks NoiseGard® active/passive function 2.0

PURPOSE OF TESTTESTFAULT ISOLATIONPROCEDURE STEP(SEE FIGURE 105)

TEST NAME

Test Procedure OutlineFigure 103

E. Introduction to HMEC 25 Troubleshooting

(1) Test Procedure Contents

To aid in determining the most direct approach to troubleshooting, especially on units with specificcomplaints, an outline of the test procedure contents (figure 103) is provided. The outline lists each test,the purpose of the test, and refers to a particular section in the fault isolation procedure should a test fail.


23-41-35

Fault Isolation ProcedureFigure 105 (Sheet 1 of 3)

REMARK: Further measurements are not recommendable. Refer to page 105/paragraph 2.D foramendments given towards handling NoiseGard® active noise compensation.


Page 106June 29/98

TP3/4 TP5/6HMEC 25NoiseGard®

Circuit CardAssembly TP2

TP1

TESTSTEP RESULTSCIRCUIT COMMENTS

1.0 NoiseGard® DC VOLTAGE

1.1 Supply voltage (internal).Check from TP3/4 to TP2 (gnd). + 6 V dc. Check C19/21.Check from TP5/6 to TP2 (gnd). – 6 V dc.

1.2 Supply voltage electret mic capsule. + 5 V dc. Check C18, R1.Check from TP1 to TP2 (gnd).

1.3 Bias voltage output amplifier.Check from Q5/7 (collector) + 6 V dc. Check Q5/7.to TP2 (gnd).Check from Q6/8 (collector) – 6 V dc. Check Q6/8.to TP2 (gnd).

DVM DC/DC CONVERTER

(XLR 3-pin)

+12 V+12 to 35 V

23-41-35


Page 107June 29/98

Fault Isolation ProcedureFigure 105 (Sheet 2 of 3)


REMARK: Further measurements are not recommendable. Refer to page 105/paragraph 2.D foramendments given towards handling NoiseGard® active noise compensation. For exactcomponent location refer to pages 108/109.

AF-meter

SINE - WAVEGENERATOR

NoiseGard® Compensation Circuit

No servicing/repairing of any electroniccomponents within NoiseGard®

Compensation Circuit. Refer to page105/paragraph 2.D.

m

Active Audio Circuit

Passive Audio Circuit

Audio frequency1 kHz /775 mV ac HMEC 25 NoiseGard®

Circuit Card Assembly

2.0 NoiseGard® SIGNAL PROCESSING

Passive* Active* CompensationAudio signal Audio signal Circuit

2.1 OK NOP NOP Check NoiseGard® ± 6 V supply voltage.Check from TP3 and TP6 to TP2 (gnd).

2.2 OK NOP OK Check C7/14, Q5/6, R13/19, U1-2/3-1/4-2.

2.3 NOP OK OK Check Q3/4/7/8, R20.

2.4 NOP NOP OK Check C8/9.Check cable (TP7/8 and TP9/10 to JackPlug) for loose or intermittent connection.

TESTSTEP

RESULTSCIRCUIT

*pass.= NoiseGard® off act. = NoiseGard® on


23-41-35

HMEC 25 NoiseGard® Circuit Card Assembly,Maintenance Aid Diagram

Figure 107

Page 108June 29/98

Component side

Solder side

+

23-41-35

CO

MPO

NEN

T MAIN

TENAN

CE

MAN

UAL w

ith IPLHM

EC 25-KAXPART N

O 025-230-415

HMEC 25 N

oiseGard

® Circuit Card Assembly,

Schematic Diagram

Figure 108

Page 109June 29/98


23-41-35

HMEC 25-KAX Schematic DiagramFigure 109

Page 110June 29/98

(Solder side)

Ground +(12 - 35) V

23-41-35

CO

MPO

NEN

T MAIN

TENAN

CE

MAN

UAL w

ith IPLHM

EC 25-KAXPART N

O 025-230-415

Page 111June 29/98

HMEC 25 W

iring DiagramFigure 110

green green

yellow

white

whitebrown

screen

white/screen

orangeblue/screen

Connecting cable

Microphone side Headphone side

transducercapsule

compensatingcapsule KE4

>>>>

greenscreen

bluered

screen

browntransducercapsule

compensatingcapsule KE4

>>>>

greenscreen

bluered

brownwhitegreen

Headband cable

brown

Microphone armMKE 45 MicrophoneTP 4

TP 9white/screen

brown

red

CO

MPO

NEN

T MAIN

TENAN

CE

MAN

UAL w

ith IPLHM

EC 25-KAXPART N

O 025-230-415

23-41-35Page 112

June 29/98

HMEC 25-KAX Connecting Cable

Figure 111

Front view

Input +12 to 35 V Ground

5

3

23-41-35


Page 301June 29/98

DISASSEMBLY

1. Introduction

Disassemble the HMEC 25 Boomset only when repair is necessary and only to the extent necessary toeffect repair. Perform the performance tests and the fault isolation test given in the Testing andTroubleshooting section to determine if and what disassembly is required.

Procedures are in the order of disassembly from the highest to the lowest subassembly. Disassemble onlyas far as indicated by the nature of the fault. The order of disassembly of electronic equipment can usuallybe determined by inspection. Special techniques, cautions, warnings, and unique procedures, whenrequired, are in this section.

2. Precautions and General Techniques

Mark, or otherwise identify, all disconnected electrical wiring. Make note of coding, placement of leads,and methods of applying insulation (if any) before unsoldering or removing any electrical parts.

WARNING: REMOVE POWER BEFORE DISASSEMBLING ANY PORTION OF THE EQUIPMENT.DISASSEMBLING THE EQUIPMENT WITH THE POWER CONNECTED IS DANGEROUS TO LIFEAND ALSO MAY CAUSE VOLTAGE TRANSIENTS THAT CAN DAMAGE THE EQUIPMENT.

CAUTION:

REFER TO ESDS HANDLING CAUTION IN ADVISORIES PARAGRAPH IN MANUAL INTRODUCTION.

3. Procedure

NOTE: Numbers in parenthesis refer to item numbers on the referenced figures in the Illustrated Parts List.When an IPL item number is followed with a lettered suffix (25A, 25B, 25C, etc) that is used to list differentpart numbers for a given item required by use-on codes, only the basic IPL item number (25) is referencedin the following procedures.

CAU

TIO

N CAU

TION




23-41-35

A. EAR PAD DISASSEMBLY (Refer to figure 301)

(1) Place headphone capsule (1) face down on work surface and hold it in position with one hand.Remove the ear pad (2) with other hand.

Page 302June 29/98

HMEC 25 Headphone Capsule DisassemblyFigure 302

HMEC 25 Ear Pad DisassemblyFigure 301

2

1

5

3

4

6

B. HEADPHONE CAPSULE DISASSEMBLY (Refer to figure 302)

(1) Insert a screw driver between rim of capsule housing (3) and headphone capsule (4).

(2) Lever headphone capsule (4) out ofcapsule housing (3).

(3) Unsolder wires and capsuleconnectors from circuit cardassembly (5).

(4) Remove circuit cardassembly (5)and foam pad (6).

23-41-35


HMEC 25 Microphone Arm Holder DisassemblyFigure 303

Pages 303/304June 29/98

C. MICROPHONE ARM HOLDER DISASSEMBLY (Refer to figure 303)

(1) Loosen retain-clip (7) and pull microphone arm (8) out of its guide notch.

(2) Loosen Phillips screws (9) and remove microphone arm holder as illustrated.

9 7

8

23-41-35


Pages 401/402June 29/98

CLEANING

1. Introduction

This section presents the unique special instructions necessary for cleaning parts and disassembledassemblies of this equipment. For standard cleaning instructions, the technician should follow theinstructions outlined in the Standard Shop Practices.

2. Cleaning Materials

Cleaning materials required to clean special areas of this equipment are listed in figure 401. Equivalentsubstitutes may be used.

MATERIAL RECOMMENDED TYPE

Isopropyl alcohol Various

Watchmaker tissues Various

Cleaning MaterialsFigure 401

3. Procedures

WARNING: OBSERVE ALL WARNINGS AND CAUTIONS LISTED IN THE ADVISORIES PARAGRAPH OF THISMANUAL.

CAUTION: DO NOT REUSE TISSUES FOR CLEANING; DO NOT REUSE OR CONTAMINATE THE CLEANINGSOLUTION BY REDIPPING THE TISSUE INTO THE CLEANING SOLUTION CONTAINER.

23-41-35


Pages 501/502June 29/98

CHECK

1. Introduction

This section presents the unique special instructions necessary to verify the condition of disassembled andcleaned assemblies of this equipment. For standard equipment checks, the technician should follow theinstructions outlined in the Standard Shop Practices manual.

2. Procedures

WARNING: OBSERVE ALL WARNINGS AND CAUTIONS LISTED IN THE ADVISORIES PARAGRAPH OF THISMANUAL AND THE STANDARD SHOP PRACTICES.

A. Check all parts for perfect mechanical operation.

23-41-35


REPAIR

1. Introduction

This section presents the unique special instructions necessary for the repair of disassembled assembliesof this equipment. For standard repair procedures, the technician should follow the instructions outlined inthe Repair section of the Standard Shop Practices.

2. Repair Supplies

No special supplies are required to repair this equipment.

3. Procedures

WARNING: OBSERVE ALL WARNINGS AND CAUTIONS LISTED IN THE ADVISORIES PARAGRAPH OF THISMANUAL AND THE STANDARD SHOP PRACTICES.

No special procedures are required to repair this equipment.

Pages 601/602June 29/98

23-41-35


Page 701June 29/98

ASSEMBLY (INCLUDING STORAGE)

1. General

This section presents instructions for assembling the HMEC 25 Boomset. Procedures are in order of thelowest major part or subassembly and proceed to a completely assembled unit. All necessary repairs orreplacements should be made before beginning assembly procedures.

2. Precaution and General Techniques

CAUTION:

REFER TO ESDS HANDLING CAUTION IN ADVISORIES PARAGRAPH IN MANUAL INTRODUCTION.

CAUTION: WHEN REPLACING A SOLID-STATE COMPONENT, USE A HEAT SINK ATTACHED TO THELEADS TO PREVENT DAMAGE TO THE DEVICE. SOLDER IRON SHOULD BE GROUNDEDPROPERLY WITH RESPECT TO BOARD OR CHASSIS WHEN REPLACING LOW-VOLTAGEDEVICES (DIODES, TRANSISTORS, INTEGRATED CIRCUITS, ETC).

CAUTION: BEFORE REPLACING MODULES OR SUBASSEMBLIES, DISCONNECT POWER FROM THEHMEC 25. FAILURE TO COMPLY WILL CAUSE DAMAGE TO ELECTRICAL COMPONENTS.

A. Wiring

NOTE: Before soldering any part, refer to notes on color coding, placement of leads, and wireinsulation made during disassembly. If not available, determine by examining a unit known to becorrect.

(1) All wire connections are to be soldered as specified in MIL-S-6872 using rosin-cor4 solder, FederalSpecification QQ-S-5716 composition Sn 60.

(2) Replace electrical wiring with wire of the same size and color code as that removed.

(3) Lace all electrical harness and tie at all breakouts. Lace ties should be approximately 13 mm (1/2 in)apart. Use Dacron lacing cord, nonwaxed lacing cord, or Tyraps.

3. Detailed Assembly Procedures

NOTE: All item numbers in parenthesis refer to item numbers on the referenced figures in the IllustratedParts List. When an IPL item number is followed with a lettered suffix (25A, 25B, 25C, etc) that isused to list different part numbers for a given item required by use-on codes, only the basic IPLitem number (25) is referenced in the following procedures.

CAU

TIO

N CAU

TION




23-41-35Page 702

June 29/98

HMEC 25 Microphone Arm Holder AssemblyFigure 701

A. MICROPHONE ARM HOLDER ASSEMBLY (Refer to figure 701)

(1) Assemble microphone arm holder as illustrated and secure Phillips screws (9).

(2) Push microphone arm (8) onto its guide notch and secure with retain-clip (7).

9 7

8

23-41-35


Page 703June 29/98

HMEC 25 Headphone Capsule AssemblyFigure 702

HMEC 25 Ear Pad AssemblyFigure 703

2

1

B. HEADPHONE CAPSULE ASSEMBLY (Refer to figure 702)

(1) Place circuit card assembly (5) and foam pad (6) in capsule housing (3) in sequence as below.

(2) Solder wires and capsule connectors on circuit card assembly (5) in the same position whendisassembling.

(3) Fit headphone capsule (4) in capsule housing (3) matching with the notch guide.

C. EAR PAD ASSEMBLY (Refer to figure 703)

(1) Place headphone capsule (1) face down on work surface and hold it in position with one hand.Mount ear pad (2) with other hand.

5

3

4

6


23-41-35

4. Final Testing

After all repairs have been made and the HMEC 25 has been reassembled, the unit should be checkedaccording to the procedure in the Testing section.

5. Storage Instructions

Ensure all subassemblies are secured to the chassis. Place the equipment in the original container ifavailable. Do not store in polyurethane bags for longer than a few month. Before storing the equipment,include a desiccant. At no time should the ambient temperature of the storage area fallbelow – 20 °C (– 4 °F) or rise above + 70 °C (158 °F).

Page 704June 29/98

23-41-35


FITS AND CLEARANCES

The fits and clearances that must be observed during assembly of this equipment are indicated, whereapplicable, in the Assembly section of this manual.

Pages 801/802June 29/98

23-41-35


SPECIAL TOOLS, FIXTURES, AND EQUIPMENT

1. Test Equipment/Resource Requirements

Figure 901 provides the minimum use specifications (MUS) for the test equipment resources required toperform test and alignment procedures for the HMEC 25 Boomset. The MUS are the generic technicaldescription, by parameter and characteristic, of the test equipment/resources required independent of aspecific manufacturer’s model, and are provided to aid in utilization of existing or alternate test resources.Unless otherwise specified, only one unit of each test equipment/resource is required.

A unit-under-test (UUT) requirement to test resource capability ratio of 1:1 was used to derive all accuracyparameter characteristics. The test performing activity should utilize test equipment/ resource withcapability that exceeds the identified accuracy characteristic in accordance with applicable local test andmeasurement integrity control to those listed as representative, as other equipment may be entirelysatisfactory if specified and recalibrated as necessary to maintain that capability.

REPRESENTATIVETYPE

ITEM(MUS

REF NO) NO CHARACTERISTICFUNCTION/PARAMETER

MAINTLEVELCODE

MINIMUM USE SPECIFICATION

Page 901June 29/98

Tools, Fixtures, and EquipmentFigure 901 (Sheet 1 of 4)

Oscilloscope 1.0 Vertical characteristics Hitachi V-1150 IIITektronix R5440

1.1 Modes of operation 2-channel

1.2 Bandwidth Dc to 10 MHz

1.3 Signal amplitude range (p-p) 10 mV to 200 V

1.4 Input impedance > 10 MΩ

1.5 Deflection factor range 2 mV/div to 5 V/div

1.6 Deflection factor accuracy ± 3 % of signal dis-play (p-p)

1.7 Input coupling Ac / dc

1.8 Maximum input 50 V dc, 200 V ac

1.9 Trigger source Internal, external,channel A, channel B

(Cont) 2.0 Horizontal characteristics


23-41-35

REPRESENTATIVETYPE

ITEM(MUS


MAINTLEVELCODE


Page 902June 29/98


Oscilloscope 2.1 Sweep modes Norm, auto single(Cont)

2.2 Sweep ranges 1 µs to 1 s/div

2.3 Time base (sweep) accuracy ± 3 %

2.4 Sweep trigger modes Dc, ac and/or edge,single sweep, norm,auto

2.5 Delay time base Not applicable

3.0 General

3.1 Remote operation Optional

3.2 Functions All

AF-meter 1.0 Ac voltage function Sennheiser II, IIIUPM 550-1

1.1 Amplitude range 30 µV to 300 V

1.2 Frequency range 10 Hz to 100 kHz

1.3 Accuracy ± 3 % of reading

1.4 Input impedance 1 MΩ / 50 pF

1.5 Display Ac V (rms)

1.6 Dynamic properties according toDIN 45633 andDIN 45500

1.7 Input level potentiometer 0 dB to -10 dB

2.0 Integrated filter

2.1 1000 Hz stop filter Attenuation at1000 Hz > 66 dB

23-41-35


REPRESENTATIVETYPE

ITEM(MUS


MAINTLEVELCODE


Page 903June 29/98


Audio 1.0 Frequency range 5 Hz to 500 kHz Leader LAG-126 IIIGenerator

1.1 Output waveform Sine and squarewave, selectable

1.2 Attenuator 10 dB x 7, 1 dB x 9,0.1 x 9 dB, fineadjuster for sinewave

1.3 Output impedance 600 Ω ± 3 %,unbalanced

2.0 Sine wave function

2.1 Maximum output voltage + 10 dB ± 0.3 dB,with a dBm - dBVchangeover switch

2.2 Distortion factor Less than 0.005 % :20 Hz to 20 kHzLess than 0.01 % :10 Hz to 50 kHzLess than 0.1 % :5 Hz to 500 kHz

2.3 Level flatness ± 0.2 dB :5 Hz to 20 kHz± 0.5 dB :20 kHz to 500 kHz

3.0 Square wave function

3.1 Maximum output voltage Approx. 4 V p-p

3.2 Rise - time Less than 200 ns

3.3 Overshot Less than 5 % athigher than - 30 dBV


23-41-35

REPRESENTATIVETYPE

ITEM(MUS


MAINTLEVELCODE


Page 904June 29/98


Impedance 1.0 Test frequencies 63 Hz, 250 Hz, Sennheiser ZP 3 IImeter 1 kHz, 4 kHz, 8 kHz,

16 kHz

1.1 Display 3 1/2 digits

1.1 Measuring ranges 19.99 Ω to1.999 MΩ

1.2 Accuracy ± 5 %

1.3 Capacitances 5 pF to 2000 µF

1.4 Inductances 10 µH to 5000 H

23-41-35


Page 1001June 29/98

ILLUSTRATED PARTS LIST

1. Introduction

The purpose of this parts list is for identification, requisition, and issuance of parts. Parts listed meetcritical equipment design specification requirements. Use only part numbers specified in this parts list forreplacement of parts.

A. Detailed Parts List

FIG-ITEM Column—Digits are item numbers assigned in sequence to correspond with item numbers on theillustration.

PART NO Column—Listed are standard Sennheiser part numbers. Sennheiser part numbering systemconsists of 5 digits.

AIRLINE PART NO Column—Part numbers will be included by the airlines as applicable.

INDENT Column—Items are coded 1, 2, 3, etc, to indicate the relationship to the next higher assembly.

NOMENCLATURE Column—Listed are the noun name, modifier, descriptive information, and reference toother figures. REV (Revision Identifier) dash (—) denotes original, letter A first change, letter B secondchange, etc. Service Bulletins are identified by SB 1, SB 2, etc. Electrostatic Discharge Sensitive devicesare identified by (ESDS). Refer to the Advisories at the front of the manual for proper handling of theseparts.

EFFECT CODE Column—Part variations within a group of equipment are indicated by a letter code (A, B, C,etc). Absence of a code indicates part applies to all models.

UNITS PER ASSY Column—Quantities specified are per item number.


23-41-35Page 1002June 29/98

HMEC 25-KAX Boomset AssemblyFigure 1

150

160

20

80

10

120

30

140

130

100

110

70

170

50

40

90

90

60

23-41-35


Page 1003June 29/98

DETAILED PARTS LIST

EFFECTCODE

AIRLINEPART

NUMBER

INDENT

UNITSPERASSY

FIG-ITEM PART NUMBER NOMENCLATURE

1-001 025-230-415 1 Boomset HMEC 25-KAX for Airlines RF1-010 48234 2 Split headband 11-020 75550 2 Dyn. headphone capsule with PCB, Replacement 21-030 70743 2 Microphone arm holder 11-040 58877 2 Electret microphone with amplifier 11-050 75818 2 Cable 1.8m / jack 6.3m + 5.25s + XLR-3M 11-060 24821 3 Ring RD7.0, 6.0x2.5 (strain relief for 1-050) 11-070 75527 2 Annular earpad, pair 11-070A 69417 2 Annular earpad, pair, velour 11-080 58715 2 Cable 500mm 11-090 24812 3 Ring RD5.0, 4.2x1.5 (strain relief for 1-080) 31-100 59997 2 Flexible microphone arm with plug 11-110 19849 2 Strain relief 11-120 57122 2 Sleeve RDI1.8x3.0 31-130 57124 2 Sleeve RDI3.5x16.5 11-140 75427 2 Cap, microphone side 11-150 75464 2 Cap housing HMEC 25-KAX 11-160 50722 2 Type plate 11-170 44740 2 Clip 1


23-41-35Page 1004June 29/98

HMEC 25 Microphone Arm Holder AssemblyFigure 2

2030

10

40

50 70

60

60

23-41-35


DETAILED PARTS LIST

EFFECTCODE

AIRLINEPART

NUMBER

INDENT

UNITSPERASSY

FIG-ITEM PART NUMBER NOMENCLATURE

2-001 70743 1 Microphone arm holder RF2-010 44619 2 Base for microphone arm 12-020 39796 2 Disk spring 12-030 19846 2 Ring 12-040 33320 2 Pressure spring 12-050 33321 2 Stop pin 12-060 46590 2 Lens screw M2x8 DIN7985 22-070 19848 2 Cap 1

Page 1005/1006June 29/98

Documents

23413500