Sigtronics RMS-640 Installation Instructions - Manual (Page 5)

page 5
UPGRADING A ST-400 INSTALLATION TO A ST-440
Intercom Chassis Mounting
The SAS unit is specifically designed to easily replace a
SPA. The panels are exactly the same dimensions (1” x 2.5”),
however the SAS units are 1 3/4” longer than the SPA units.
Make sure that you have the extra depth required behind
your panel. The five mounting holes are exactly in the same
positions. Only the center hole will have to be changed
(enlarged from 1/4” to 1/2”).
To upgrade, first remove the SPA unit from the aircraft panel.
This is done by unscrewing the two Phillips head screws and
the nut on the ON/OFF switch. Remove the printed SPA
panel. Pull the SPA unit out and unplug the white connector
from the RES cable. Next, drill the center hole in the aircraft
panel out to 1/2”. Then to mount the SAS chassis per the
“Mounting Chassis” instructions on page 2.
Unplug all four connectors going to the RES switcher unit.
Remove the RES unit from its mounting chassis by removing
the four corner screws. Remove the RMS switcher unit from
its chassis similarly. Put the RMS switcher into the RES
chassis and secure.
Disconnect the RES music input cable (J3) from the music
source and install the RMS input cable per Notes 8 and 10
under “WIRING INSTRUCTIONS” on page 4.
Remove the RES switch harness and Panel by removing
the two 1/4” nuts on the switch bushings. Disconnect the
wires from the intercom stereo headphone jacks. Install the
RMS switch harness and Panel per paragraphs 2, 3, and 4
under the “SWITCHERHARNESSINSTALLATION” section
on page 2.
Rewire all the stereo headphone jacks per Figure 3.
INSTALLATION CHECK-OUT AND
ADJUSTMENTS
After the system is installed, again check that the SAS and
RMS unit chassis, jacks, and wiring harnesses are clear of
all aircraft operating controls and cause no interference with
them. Check out the Stereocom installation by following the
instructions:
Plug in all the headset mic and phone plugs into the
respective intercom jacks. Put on the pilot’s headset and
position the boom mic close to the mouth, as is the practice
with a hand-held mic. Voice clarity is best when the mic is at
one side of the mouth and 1/4” from the lips.
To assure that the aircraft radios, pilot’s headset, and PTT
switch are connected and functioning properly, turn the SAS
units OFF/ALL/ISO switch to the “OFF” position. Turn the
PILOT and PASSenger MUSIC ON/OFF switches “OFF”.
If applicable, set the aircraft audio panel to “Headphone”
position. Then turn on the aircraft radio(s) as usual, and
verify that the pilot can hear the radios and can transmit
using his push-to-talk switch and headset. Aircraft radio(s)
and audio panel should operate exactly as they did before
the Stereocom system was installed. Aircraft radio reception
should be heard in the pilots headset. Aircraft radio reception
should not be heard in the co-pilot or passenger headsets.
There should be no intercom between headsets with the SAS
unit turned “OFF”.
Next turn the SAS unit OFF/ALL/ISO switch to the “ALL”
position. Set the SAS volume control to mid-position. Verify
that all headset positions can now intercom with each other,
including the passengers. Verify that both pilot and co-pilot
can operate the aircraft radio(s). In this mode all headsets
on the intercom will hear the aircraft radio(s).
It may be necessary at this time to adjust the SAS unit
transmit mic output to the aircraft radios. A small adjustable
potentiometer is provided inside the unit for this purpose. It
is accessible through a hole in the side of the SAS chassis.
It is marked “MOD. ADJ.”, and can be adjusted with a small
blade screwdriver. In the event of over-modulation (garbled)
or reports of weak transmission’s over the aircraft radio, an
appropriate adjustment can be made. Clockwise rotation
increases the output level to the aircraft radio mic input.
Counter-clockwise rotation decreases modulation level.
This adjustment sometimes needs to be made after the initial
installation of the intercom or if a new radio is installed. (The
output is set for unity gain at Sigtronics).
To verify music operation, connect your music source to the
music input jack, if applicable. Turn on the music source
and set volume to low level. Next turn “ON” the PILOT and
PASSenger Stereocom MUSIC ON/OFF switches. When the
aircraft radio and intercom are quiet you will hear music in the
headsets. Adjust the music source volume to a comfortable
level. Verify that music is heard in all headsets and is
interrupted by intercom conversations. If everything checks
out, refer to the ST-440/ST-640 STEREOCOM OPERATING
INSTRUCTIONS for proper use and other operating modes
of the Sigtronics Stereocom system. If something does
not work as described, carefully go over the system wiring
again. If ok, refer to the following section for helpful hints and
solutions to common problems:
HELPFUL HINTS AND TECHNICAL
INFORMATION
SAS-440/SAS-640 Sidetone Modification
Most aircraft radios, when transmitting, provide what is called
“sidetone”. Without sidetone, you will not hear yourself or your
co-pilot transmit to ATC. This can be distracting, especially
during instruction, because no one on the intercom will
hear the outgoing transmission of the radio conversation.
Some aircraft radios, however, do not provide this function.
Also, some radios are designed to drive only one headset.
Therefore, if you have such a radio, the sidetone may be
extremely weak or nonexistent.
If this is the case and the sidetone cannot be turned up in
the radio(s), a simple modification can be performed within
the SAS unit to simulate sidetone. The SAS requires partial
disassembly to accomplish this modification. First unplug and
remove the SAS unit from the aircraft. To disassemble unit,