Northern Airborne Technology 251 - Manual (Page 23)

Model 251 Passenger Speaker Amplifier
SM251 Installation and Operation Manual
Section 3 Rev: 1.00 Issue 2 Page 3-1
ENG-FORM: 806-0114.DOT
CONFIDENTIAL AND PROPRIETARY TO NORTHERN AIRBORNE TECHNOLOGY LTD.
Section 3 Operation
3.1 Introduction
Information in this section consists of functional and operational procedures for the Model 251 Passenger
Speaker Amplifier.
.
3.2 General Information
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.
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.
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).
The Model 251 Passenger Speaker Amplifier has no operator accessible controls. During installation, it
may be determined that internal level adjustments are required. Qualified personnel only shall complete
internal level adjustments.
Section 3 ends