Sigtronics EAI Operating Instructions - Manual (Page 8)

3. Check for open headset jack barrel connection (black wire).
The open could be anywhere along the black wire connec-
tion between the jack and the EAI unit.
4. Check for a microphone line (white / black, white / orange,
or tan wires) shorted to the headphone line (blue wire). The
short could be at one of the headset jacks or in the wiring
between the unit and a jack.
Note that for 2 and 3 above, it will only squeal if a headset
is actually plugged into the specific jack that is wired incor-
rectly.
PTT Test:
If all above is good, make sure all headsets are plugged into
their respective jacks. Put on the Engineer’s (driver) headset
and position the microphone as usual. Press the Engineer’s
PTT switch. While continuing to hold down the switch, talk
into the mic and verify that you can still hear yourself. Also,
while holding down the PTT switch, verify that none of the
other head set microphones are active. Release the PTT
switch.
Now put on the Captain’s headset, position the microphone,
and press the Captain’s PTT switch. Verify that only Captain’s
head set microphone is active as his switch is held down.
If the system has a jack and PTT wired up at the vehicles pump
panel, unplug the headset from the drivers position and plug
it into the pump panels jack. Press and hold down the pump
panel PTT switch. Verify that only the pump panel headset
microphone is active.
If all works fine, skip down to “Electrical Noise Test” on this
page. If anything does not work as above, you have one of
three possible PTT switch wiring errors:
1. PTT line (white / red or white / blue wires) open or not
connected between a PTT switch and the EAI unit.
2. Open or missing return line (black wire) to a PTT switch.
3. Reversed PTT lines. The Engineers PTT line connected to
the Captain’s PTT switch and visa versa.
Electrical Noise Test:
The last thing to do before the radios are hooked up to the
unit is a simple noise test to verify system wiring as well as
vehicle electrical system integrity.
1. Unplug all intercom headsets except for the drivers.
2. Make sure all the EAI panel controls and switches are set
as in “System Setup” on page 6.
3. Start the vehicles engine and let it idle a bit. This is a station-
ary test - the vehicle should not be moving and should be
in “PARK” or “NEUTRAL” with brakes set.
4. Close all vehicle windows and doors to eliminate as much
background noise as possible.
5. Turn on as much vehicle electrical equipment as possible.
This usually means all lights and strobes. Do not turn on
sirens or horns.
6. Put on the driver’s headset, position the mic, and make sure
the headset volume control is set to maximum.
7. With the vehicle still in “PARK” or “NEUTRAL” and brakes set,
slowly increase the vehicle engine rpm from idle to about
1500 RPM and back again. While doing this, listen for any
whine or hum in the headsets. Except for some possible
engine background noise being picked up from the head-
set microphone you should not hear any “Electrical” whine
or hum in the headset.
8. Shut off the vehicle engine as well as the lights, strobes,
etc. If, while the engine was running, there was no electrical
noise, skip down to “Radio Hook Up” on page 9. If you did
hear electrical noise, use the following to track down the
problem:
Turn the vehicle power off and disconnect the EAI ground
connection (green wire) from ground. Turn on the vehicle
power (engine off), put on the driver’s headset and see if
the intercom part of the EAI unit is working.
If You Can Hear Yourself In The Headset:
1. Then the EAI intercom return wire (black) is incorrectly
grounded to the vehicle chassis. Look for:
a) A headset jack barrel touching the vehicle chassis. Most
common when a headset jack is mounted directly into
the vehicle’s panel without using the supplied insulat-
ing washers or incorrectly installing the washers.
b) The black wire pinched or cut and shorting to the vehi-
cle chassis. This can be anywhere along the intercom
wiring as the black wire goes to all head set jacks and
PTT switches.
2. Once the problem has been found and fixed, again make
sure that the intercom now does not work with the green
wire disconnected. You could have the black wire grounded
in more than one spot.
3. The next step is to reconnect the green wire and do the
electrical noise test again to assure that you have fixed all
possible noise problems.
If You Cannot Hear Yourself In The Headset:
The intercom wiring is correct, but excessive electrical noise
from the vehicle’s power system is affecting the EAI unit
operation. This noise is getting into the unit on the EAI power
wires (red and green). There are basically two types of power
line electrical noise sources:
1. Noise generated directly by the vehicle’s electrical/charging
system - most commonly known as alternator whine. This
is only present when the vehicle’s engine is running and
recognized by the fact that the pitch or frequency of the
whine changes directly with the change in engine rpm.
(Higher frequency at higher engine rpm’s and lower fre-
quency at lower rpm’s.)
The preferred way to solve this type of problem is to have
the vehicle’s electrical / charging system serviced. The most
common cause of this type of noise is bad diodes in the
vehicle’s alternator. Other possible causes are: bad vehicle
voltage regulator; bad alternator or battery cable con-
nections; missing or bad engine or alternator grounding
straps.
If servicing the vehicle’s charging system is impracti-
cal, installing a good alternator whine power line filter
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