CSP-HMI-3 MD Helicopters, Inc.
MAINTENANCE MANUAL
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Revision 12
97-06-00
The information disclosed herein is proprietary to MD Helicopters, Inc.
Neither this document nor any part hereof may be reproduced or transferred to
other documents or used or disclosed to others for manufacturing or any other
purpose except as specifically authorized in writing by MD Helicopters, Inc.
Copyright © 1999−2016 by MD Helicopters, Inc.
amplification on J509 pin C, E, F, H,
and J. When a RADIO-ICS switch at
one of the passenger intercom stations
or on the pilot's or copilot's cyclic stick is
pressed to the ICS position, one of J509
pins aa, bb, cc, X or Z goes lo; the ICS
keying circuit in turn operates, enab
ling the amplified signals to be routed
out on J509 pins U and V to the
common phone hi audio line for distri
bution to headset earphones at all
intercom stations.
During radio transmission, the pilot's
(or copilot's) microphone audio signal is
routed un-amplified out on J509 pin D
to the transmitter of the vhf COMM
transceiver.
Microphones are supplied operating
voltage from the ICS control unit via
J509 pins C, E, F, H and J.
(2). Receiver Audio:
Audio signals incoming from the
various receivers on J509 pins K, L, M,
N and P are amplified and distributed
to headset earphones at the intercom
stations. The amplified signals are
present across J509 pins U and V
during both ICS operation and radio
transmission.
(3). Transmit Keying:
When the pilot's (or copilot's) RADIO-
ICS switch is pressed to the RADIO
(transmit) position, a transmit keying
control signal (ground) is input on J509
pin W (or pin X) to disable the ICS
keying function.
The transmit keying ground is routed
out on J509 pin dd to the transmitter of
the vhf COMM radio transceiver, to
activate radio transmission.
(4). Radio Transmit Audio:
When the RADIO-ICS switch on the
pilot's or copilot's cyclic stick is pressed
to the RADIO position, J509 pin W or
pin X goes lo to activate the radio
transmit keying function. The un-am
plified audio signal from the micro
phone is in turn routed out on J509 pin
D to the transmitter of the selected vhf
COMM transceiver for radio transmis
sion.
(5). Sidetone Audio:
During radio transmission, sidetone
audio signals from the transmitter of
the vhf COMM 1 transceiver are input
on J509 pin R, amplified and routed out
J509 pins U and V for distribution to
headset earphones at all intercom
stations. Signals from a second vhf
COMM radio (if installed) are input on
J509 pin S and processed in the same
manner.
G97-0601
RADIO
COMM 1
COMM 2
XMIT
COM 1
COM 1
OR
O
F
F
Figure 1. Radio Selector Switch
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