MD Helicopters 369D - Amplifier Replacement; Replacement of System Component; Wiring Diagram

CSP-HMI-3 MD Helicopters, Inc.
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Table 201. Troubleshooting − Public Address and Siren System (Cont.)
Symptom Corrective ActionProbable Trouble
No audio when public address
position is selected on control unit.
Microphone disconnected or
defective.
Connect or replace microphone.
Defective circuits in control unit. Replace control unit.
Disconnected or defective wire
harness between amplifier and
control unit.
Connect or replace wire harness
between amplifier and control unit.
No audio when siren position is
selected on control unit.
Defective siren circuits in amplifier. Replace amplifier.
Defective circuits in control unit. Replace control unit.
Disconnected or defective wire
harness between amplifier and
control unit.
Connect or replace wire harness
between amplifier and control unit.
No audio at loudspeaker(s).
Disconnected terminals at
loudspeaker(s).
Connect terminals at loudspeaker(s).
Damaged loudspeaker(s). Repair or replace loudspeaker(s).
3. Wiring Diagram
For the public address and siren system wiring
diagram, refer to Figure 202.
4. Replacement of System Component
A. Amplifier Replacement
(Ref. Figure 201)
(1). Verify BATTERY-OFF-EXT PWR
switch at OFF position.
(2). Open floor access door on left side of
pilot's compartment for access to
electronics compartment and amplifier.
(3). Disconnect wire harness assemblies
from amplifier at connectors P558,
P559 and P560.
(4). Loosen and remove four screws and
washers from amplifier support.
Remove amplifier and attached sup
ports from channel assembly in com
partment.
(5). Prepare replacement amplifier as
follows:
NOTE: A good structural electrical bond
(ground) must exist between amplifier and
channel assembly mounted in electronics
compartment.
(a). Remove bolts and washers securing
supports on removed amplifier.
Discard bolts and washers but retain
supports for installation.
(b). Remove and discard supports pro
vided on replacement amplifier.
Retain bolts and washers for installa
tion.
(c). Install supports retained from
removed amplifier and secure to
replacement amplifier with new bolts
and washers.
(d). Check and make certain that 15
ampere fuse is installed in amplifier.
(6). Install amplifier in electronics compart
ment and secure amplifier and attached
supports to channel assembly with
washers and screws.
(7). Connect wire harness assemblies (-15,
-17, -19) to amplifier at connectors
P558, P559 and P560.
(8). Perform system operational check.
(9). Close and secure floor access door on
left side of pilot's compartment.