Northern Airborne Technology AA21-4xx - Manual (Page 20)

AA21-400 Cabin PA System Manual SM34 Rev. 4.00
Page 2-2 Nov 10, 2003
ENG-FORM: 800-0106.DOT
Amendment #1 Jan 18, 2005
CONFIDENTIAL AND PROPRIETARY TO NORTHERN AIRBORNE TECHNOLOGY LTD.
2.3.3 Cautions
Use shielded cable exactly as shown and ground as indicated. All audio installations
can be severely degraded by incorrect wiring and shielding. Unusual buzzes, hums or
other background audio are symptomatic of multiple grounds, or noisy external systems
such as blowers or pumps sharing wiring with the audio system. Never operate any of
these units below their 8
Ω rated impedance.
2.3.4 Cabling and Wiring
All unshielded wire shall be selected in accordance with AC43.13-1B Change 1,
Paragraphs 11-76 through 11-78. Wire types should be to MIL-W-22759 as specified in
AC43.13-1B Change 1, Paragraphs 11-85, 11-86, and listed in Table 11-11. For
shielded wire applications, use Tefzel MIL-C-27500 shielded wire with solder sleeves
(for shield terminations) to make the most compact and easily terminated interconnect.
Follow the wiring diagrams in Section 2.6 as required.
Allow 3 inches from the end of the wire to the shield termination to allow the hood to be easily
installed. Note that the hood is a ‘clamshell’ hood, and is installed after the wiring is complete.
All wiring should be at least 22 AWG, except power and ground lines, which should be
at least 20 AWG. Ensure that all ground connections are clean and well secured. To
prevent system failure or inadequate equipment protection, power must be supplied
from a separate breaker or fuse and not connected to any other source.
2.3.5 Post-Installation Checks
2.3.5.1 Voltage/resistance checks
Do not attach the AA21-400 until the following conditions are met.
Check the following:
a) P101
pins <1> <2> and <3> for +28 Vdc relative to ground.
b) P101
pins <14>, <15> and <16> for continuity to ground (below 0.5 Ω).
c) P101
pins <18>, and <22> (with switches open) for infinite resistance to ground (> 10 M Ω).
d)
P101 pin <5> to pin <7> for 4 – 6 Ω (typical).