Northern Airborne Technology 250 - Manual (Page 10)

EQUIPMENT MANUAL 250-16-1
250/250-16-1 Page 1
EQUIPMENT MANUAL
MODEL 250-[ ]
1.0 OPERATING INSTRUCTIONS AND EQUIPMENT LIMITATIONS
The Model 250 Passenger Speaker Amplifier is a remotely controlled, electronic unit that operates
upon command from switches and potentiometers in the cockpit or cabin of the aircraft. The
Model 250 provides Seat Belt and No Smoking sign chime tones, a Cabin Call ringer tone, ADF,
Pilot Select Comm., TV, Briefer and Cabin Paging audio, all in mono, to the cabin speakers. It
also provides audio taken from an external AM/FM stereo receiver/cassette tape or CD player, in
stereo, to the cabin speakers.
Both 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.
All inputs and operating modes are electronically switched. Ground signals, supplied by manual
switches in the cockpit, enable the electronic switches in the Model 250. The circuitry is arranged
to give Paging and Brief audio priority; the PA MIC or Brief switch signals essentially open the
Stereo Left, Stereo Right, ADF 1, ADF 2, Pilot Select COMM, and TV audio inputs. Microphone
bias current is available from the Model 250 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. The attenuators each have approximately 30 dB (min.) of range and are
each controlled by a remote volume potentiometer. The pots required are zero to 10,000 ohm,
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 volume control attenuator for the Stereo Input to Speaker Output audio channel.
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 speakers 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 250 end plate, to set the chime or ringer levels heard in the
passenger speakers.
The Left and Right Speaker Amplifier output ratings are each 28 watts into 2 ohms (30 Watts
typical). Both speaker amplifier outputs are internally protected against open and short circuits as
well as over-temperature (>105°C).