When audio lines are balanced twisted pair, the induced noise voltage is the same on both conductors
and, therefore, cancels out before it is amplified. But when the circuit becomes unbalanced, the induced
noise voltage is not the same on both conductors and is, therefore, amplified and causes an audible hum
or buzz. To solve the problem, locate the source of the ground by checking each conductor and moving
from one junction point to the next and disconnecting the effected circuit. Improperly grounded circuits
are often the result of poor terminations such that small strands protrude and touch adjacent terminals.
In many instances, the presence of water or moisture and deposits in a junction box form a conductive
solution that causes a ground fault or leakage to ground.
Low Level Audio At All Stations
This problem can occur when there is a dead short across any channel or page line. The system will
still function but the audio level will be the lowest at the stations closest to the short. Locate the short
by checking with an ohmmeter at the junction boxes and disconnecting the effected sections.
Cross Talk
Channel and page lines are twisted pair wires and balanced such that when circuits are accidentally
crossed during installation interference between two lines will occur. Cross talk can also occur when
there is leakage or a ground fault on two of the channel lines or when there is a missing or open line
balance resistor. The resistance between the channel line circuits should be very high or infinite.
Inoperative Station
In a properly operating system an inoperative station indicates miswiring or a problem with the sta-
tion itself. Check the wiring connection. If the problem is not caused by miswiring, swap the plug-in
modules of the effected station with one that is operating properly to identify the defective module.
VI. MAINTENANCE.
SAFETY MESSAGE TO MAINTENANCE PERSONNEL
Listed below are some important safety instructions and precautions you should follow:
• Read and understand all instructions before installing or operating this system.
• Any maintenance to the SelectFone station must be done with power turned off.
• Any maintenance to the unit must be performed by a trained electrician in accordance with NEC
Guidelines and local codes.
• Never alter the unit in any manner. Safety in hazardous locations may be endangered if additional
openings or other alterations are made in units specifically designed for use in these locations.
• The nameplate, which may contain cautionary or other information of importance to maintenance
personnel, should NOT be obscured in any way. Ensure that the nameplate remains readable when
the housing’s exterior is painted.
Failure to follow all safety precautions and instructions may result in property damage, serious
injury, or death.
Other than cleaning, no regularly scheduled maintenance is required. To ensure unit is operating
properly, it should be tested at regularly scheduled intervals.
VII. SERVICE
The Federal Signal factory will service your equipment or provide technical assistance with any
problems that cannot be handled locally.
Any units returned to Federal Signal for service, inspection, or repair must be accompanied by a Re-
turn Material Authorization. The R.M.A. can be obtained from the local Manufacturer’s Representa-
tive or by calling the factory.
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