COBHAM 251 Manual de usuario
Amendment #2 Aug 9, 2011
CONFIDENTIAL AND PROPRIETARY TO COBHAM
DOCUMENT NUMBER 251-16-1
251
PASSENGER SPEAKER AMPLIFIER
1
INSTALLATION AND OPERATION MANUAL
REV "-" Sep 15, 2004
Cobham
6400 Wilkinson Drive
Prescott, AZ 86301-6164
(928) 708-1500
SEALED
2011.08.16
17:15:38
-07'00'
251-16-1 Rev. - 251 Passenger Speaker Amplifier Installation and Operation Manual
Aug 9, 2011 Page ii
ENG-FORM: 820-0109.DOT Amendment #2 Aug 9, 2011
CONFIDENTIAL AND PROPRIETARY TO COBHAM
Cobham
has acquired the assets of Nothern Airborne
Technology Ltd. and dB Systems Inc., and
has reissued this manual in its entirety
Cobham
will be responsible for all future
amendments and revisions.
251-16-1 Rev. - 251 Passenger Speaker Amplifier Installation and Operation Manual
Aug 9, 2011 Page iii
ENG-FORM: 820-0109.DOT Amendment #2 Aug 9, 2011
CONFIDENTIAL AND PROPRIETARY TO COBHAM
Periodically Cobham will release manual amendments. In order to maintain the most
accurate and up to date manual these amendments should be carried out immediately
upon receipt and recorded on the following amendment record.
AMENDMENT RECORD
Amend
ment
Number
Amendment
Date
Amendment Change Check Approve
1 Aug 3/07
2 Aug 9/11 Incorporated ECR11040.
Added 251-[ ] MOD F.
Insert any Amendment Instruction sheets after this page.
Zack Pahlman
2011.08.16
11:01:10 -07'00'
Geoff
Melton
2011.08.16
14:45:47
-07'00'
Aaron
Voigt
(Approved
)
2011.08.1
6
16:23:14
-07'00'
INSTALL_OPS
MANUAL AMENDMENT
Manual: 251-16-1 Amendment #: 2
Document #: 251-16-1 809-0002 Amendment Date: Aug 9, 2011
Amendment # 2 August 9, 2011 Page 1
ENG-FORM: 809-0109.DOT
CONFIDENTIAL AND PROPRIETARY TO COBHAM
The purpose of this amendment is to update the 251 outline drawing and MOD table
per ECR11040.
Amendment Instructions:
Remove Pages Replace With Pages
1
Title Page Amendment # 1 Title Page Amendment # 2
Page ii Amendment # 1 Page ii Amendment # 2
Page iii Amendment # 1 Page iii Amendment # 2
Page b Amendment #1 Page b Amendment #2
Page c Amendment #1 Page c Amendment #2
Page d Amendment #1 Page d Amendment #2
2Remove Drawings Replace With Drawings
251 Rev 1.51 (page 7) 251 Rev 1.70 (page 7)
2Add Drawings After Drawings
251-003 810-0 Rev 1.30 Page 15
251-006 810-0 Rev 1.00 251-003 810-0 Rev 1.30
Note: Ensure that all drawings are inserted in the order shown on the latest drawing lists.
2 Update the Amendment Record sheet at the front of the manual.
3 Insert this page into the manual after the Amendment Record sheet (page iii).
Manual Amendment ends after the following amended pages
INSTALLATION & OPERATION
MANUAL AMENDMENT
Manual: SM251 251 Series Amendment #: 1
Document # SM251\Install_Ops\809-0001 Amendment Date: Aug 03, 2004
Amendment #1 Aug 03, 2004 Page 1
ENG-FORM: 809-0107.DOT
PROPRIETARY AND CONFIDENTIAL TO NORTHERN AIRBORNE TECHNOLOGY LTD.
The purpose of this amendment is to correct the outline drawing and include the NAT
information.
Amendment Instructions:
Remove Pages Replace With Pages
1
251-16-1 Title Page, rev - SM251 Title Page, rev -
Pages b – c, rev - Pages b – d, rev -, Amendment #1
Page 7 Page 7, Amendment #1
Insert Pages After Page
2
Pages ii – iii SM251 Title Page
Add Section (to the end of the manual)
3
4.0 Supplements
4 Update the Amendment Record sheet at the front of the manual.
5 Insert this page into the manual after the Amendment Record sheet (page iii).
Manual Amendment ends after the following amended pages
EQUIPMENT MANUAL 251-16-1 REV -
251/251-16-1 Amendment #1 Aug 03, 2004 Page a
CHANGE RECORD
DATE CHANGE CHECK APPROVAL
3-11-03
ORIGINAL DOCUMENT RELEASED
AP
ML
EQUIPMENT MANUAL 251-16-1 REV -
251/251-16-1 Amendment #2 Aug 9, 2011 Page b
PROPRIETARY AND CONFIDENTIAL TO COBHAM
TABLE OF CONTENTS
Page
1.0 EQUIPMENT OPERATIONS AND INSTALLATION .................................................................1
2.0 SPECIFICATIONS ....................................................................................................................3
3.0 INSTALLATION PROCEDURES, WIRING DIAGRAM, AND LIMITATIONS............................6
3.1 PHYSICAL.................................................................................................................................6
3.2 ELECTRICAL ............................................................................................................................6
Tables
Table A Detail Part Numbers..........................................................................................................c
Table 1 Pinout Listing .....................................................................................................................9
Table 2 Environmental Qualification Form ...................................................................................14
Figures / Drawings
251 Outline, Model 251-[ ], Passenger Speaker Amplifier (Rev 1.70)....................................7
Figure 2 Model 251-[ ] Block Diagram ...........................................................................................8
Figure 3 Model 251-[ ] Wiring Diagram .......................................................................................10
Figure 4 Internal Trim Pot Adjustments.........................................................................................13
EQUIPMENT MANUAL 251-16-1 REV -
251/251-16-1 Amendment #2 Aug 9, 2011 Page c
PROPRIETARY AND CONFIDENTIAL TO COBHAM
MODEL 251 DETAIL PART NUMBER PROCEDURES AND LEVELS
The following is a tabulation of all detail part numbers available for the
Model 251 Passenger Speaker Amplifier. A Model 251 with an
associated detail part number is designated as a Model 251-XXX,
where XXX is the applicable three digit detail part number.
Table A. Detail Part Numbers
Detail Part No. Description of Detail
001 Low pass filters adjusted for -3 dB attenuation at 90 Hz on left and
right speaker outputs. High pass filters adjusted for -3 dB attenuation
at 20 Khz on left and right speaker outputs.
-001 calibration is designed for use with 4-inch speakers.
002 Identical to 251 Base Model. Part number 251-002 was created to
prevent a conflict with an existing part number 251 in customer part
system.
003 Identical to 251 Base Model with the following exceptions:
a) Briefing audio is to output through the right speaker only.
b) The receiver inputs and switches are not available.
c) The briefer switch input is externally grounded, disabling the
Stereo Left input and the Stereo Right input.
Installation information can be found in the 251-003 Installation and
Operation Manual Supplement.
006 Identical to 251 Base Model with the following exceptions:
a) The chime tones are routed to the PA sidetone audio output.
b) The chime tones are activated upon the activation of the PA
key.
Installation information can be found in the 251-006 Installation and
Operation Manual Supplement.
EQUIPMENT MANUAL 251-16-1 REV -
251/251-16-1 Amendment #2 Aug 9, 2011 Page d
PROPRIETARY AND CONFIDENTIAL TO COBHAM
SM251 FIGURES
This page lists the drawings necessary for complete maintenance and troubleshooting.
The applicable serial numbers are shown in the right hand column.
Previously only the most current revision of each figure was included in this
manual. For these figures, the rev is listed as "N/A".
Table B. Figures with Applicable Serial Numbers
FIGURE/DWG REV. DESCRIPTION TYPE SERIAL #
251 1.70 Passenger Speaker Amplifier Outline All
2 N/A Passenger Speaker Amplifier Block Diagram All
3 N/A Passenger Speaker Amplifier Wiring Diagram All
4 N/A Passenger Speaker Amplifier Internal Trim Pot Adjustment All
EQUIPMENT MANUAL 251-16-1
251/251-16-1
Page 1
EQUIPMENT MANUAL
MODEL 251
PASSENGER SPEAKER AMPLIFIER
1.0 EQUIPMENT OPERATIONS AND INSTALLATION
The Model 251 Passenger Speaker Amplifier is a remotely controlled, electronic unit that operates
upon command from remote switches and potentiometers in the cockpit or cabin of the aircraft.
The Model 251 provides Seat Belt and No Smoking sign chime tones, a Cabin Call ringer tone,
ADF, Pilot Select Comm. (PSC), Briefer, and Cabin Paging audio (all in mono) to the cabin
speakers. It also provides audio from an external AM/FM stereo receiver/cassette tape or CD
player (in stereo) to the cabin speakers and auxiliary monitor outputs.
The left and right speaker amplifier channels are each powered through separate internal fuses so
that a failure in one speaker channel will not disable the other speaker channel or the remaining
control circuitry. The left and right monitor outputs are powered from a third power supply circuit.
All inputs and operating modes are electronically switched. Ground signals, supplied by manual
switches in the cockpit, enable the electronic switches in the Model 251. The circuitry is arranged
to give audio priority to paging, briefer, and chimes; the PA MIC, BRIEF, and Seat Belt/No
Smoking chime switch signals mute the Stereo Left, Stereo Right, ADF 1, ADF 2, PSC, and TV
audio inputs. PA, briefer, and chimes will automatically enable speakers even if the speaker
switch is off. Microphone bias current is available from the Model 251 for the PA MIC microphone
input.
Electronic attenuators are employed to control paging volume and master receiver (ADF 1, ADF 2,
PSC, and TV) volume. Each attenuator has approximately 30 dB (minimum) of range and is
controlled by a remote volume potentiometer. The pots required are zero to 10,000 ohms, linear
taper, and are electrically arranged to provide maximum resistance for maximum volume. The
audio source (stereo tape cassette player, etc.) for the Stereo Left and Right inputs should have
its own external volume control attenuator for the Stereo Input to Speaker and Monitor Output
audio channels. The left and right stereo inputs are fully floating (differential type).
A musical chime tone is provided to the cabin speakers to alert the passengers of a change in the
Fasten Seat Belt or No Smoking sign status. A Cabin Call ringer tone is also provided to the
cabin for a cockpit to cabin intercom system. The chime and ringer tones do not pass through
either of the electronic attenuators. Internal screwdriver potentiometer adjustments are
accessible, after removal of the Model 251 end plate, to set the chime or ringer levels heard in the
passenger speakers.
Each left and right speaker amplifier output rating is 28 Watts into 2 ohms (30 Watts typical) or 49
Watts into 1 ohm. Both speaker amplifier outputs are internally protected against open and short
circuits as well as over-temperature (>105°C). A remote electronic ON/OFF switch for the left and
right speaker outputs is provided. A remote electronic speaker mute control is also provided. The
mute control can be connected to the aircraft’s Weight-On-Wheels switch to lower speaker
volume upon landing when lower cabin ambient noise levels are present and less speaker volume
is needed. The speaker mute control drops speaker level by approximately 1/2 (-6 dB) when
grounded.
Left and right stereo monitor outputs are provided for connecting to a cabin headphone amplifier
or headphone audio distribution system. The monitor outputs are line-level (1 V
RMS
adjustable)
outputs that carry the same audio signals as the speaker outputs. Unlike the speaker outputs, the
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