5
Next turn the SPA-4S unit "on". Set the SPA-4S volume control to
mid-position. Set SPA-4S squelch control fully clockwise. Verify
that the Pilot and co-pilot can operate the aircraft radio(s). As be-
fore, all headsets on the intercom will hear the aircraft radio(s).
Check that all headset positions can intercom.
It may be necessary at this time to adjust the SPA-4S unit 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 SPA-4S 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 transmissions over
the aircraft radio, an appropriate adjustment can be made. Clock-
wise 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 installa-
tion of the intercom or if a new radio is installed. (The output is set
for unity gain at Sigtronics).
You are now ready to check for proper wiring of the music source.
First, make sure squelch is off (full counter clockwise) and inter-
com is ON. Turn on the music source and listen for music through
pilot and co-pilot headsets, and passenger headsets. There
should be music.
If everything checks out, refer to the SPA-4S OPERATING IN-
STRUCTIONS sheet for proper use and other operating modes of
the Sigtronics SPA-4S intercom system. If something does not
work as described, carefully go over the intercom wiring again. If
something is still not right or you have any questions regarding the
installation and operation of the Sigtronics SPA-4S intercom or
any other Sigtronics product feel free to contact us directly or
email us at [email protected]. Technicians are available Mon-
day though Friday 8 am to 4:30 PM Pacific time.
See the separate SPA-4S OPERATING INSTRUCTIONS sheet
for complete operation information.
HOW TO SELECT MUSIC OPTIONS
To select either full music mute during intercom or no music mute
during intercom the unit must be removed from the aircraft. This is
done by first removing the volume and squelch control knobs with
and 0.05 inch Allen wrench. Then remove the two mounting
screws and switch nut that hold the unit in the panel. The unit is
now free for removal from the aircraft after disconnecting the ca-
bles at the plugs.
To enable either of these options, modification to the bottom of the
units’ circuit board is required.
CAUTION –
a qualified technician
should perform this modification. First remove the three screws
securing the bottom cover to the case and carefully lift and remove
the cover. Note that the circuit board does not have to be removed
from its case to complete the modifications.
To select full mute during intercom solder the two small-insulated
jumper wires at the locations specified in Figure 7.
OR...
To select no music mute during intercom cut the circuit traces with
a small sharp blade at the X’s per Figure 8.
Replace the cover and secure it with the three screws as before.
Install the unit back into the panel and plug in the two cables.
SPA-4SN PUSH-TO-INTERCOM INSTRUCTIONS
Install a separate momentary switch at each headset position.
Connect per Figure 9. To use the push-to-intercom feature, turn
the squelch control on the intercom fully counter-clockwise. Then
to activate, press the push-to-intercom switch(s). Alternately, to
use the intercom in voice activated (VOX) mode set the intercom
squelch as normal. See the separate SPA-4S OPERATING IN-
STRUCTIONS sheet.
Sigtronics Corporation
949 N. Cataract Ave, #D
San Dimas, Ca 91773
(909) 305-9399
www.sigtronics.com
SPA4SINST 10/10/2002 REV B
…when it counts!
FIGURE 7
FIGURE 8
TO
A
TO
A
(12) VIOLET
PUSH-TO-INTERCOM
SWITCHES
(1 PER HEADSET)
TO SPA-4SN
J1 PIN 12
FIGURE 9
