MAINTENANCE AND REPAIR
The best designed and built equipment occasionally
There are many factors that cause
faults: moving equipment, atmospheric conditions, and
the age of the equipment, just to name a few. A
preventive maintenance schedule should be developed
that requires a set routine of periodic tests, checks, and
inspections to head off trouble before it develops.
When repairing a PA. system, you should always
follow the manufacturers recommendations and
guidelines. Replacing faulty parts with the exact
replacement parts is always the correct procedure.
Trouble in a public address system is often caused
by nothing more than a loose connection or a break in
the cable shield. Check for simple faults of this type
before you begin a lengthy test of the system.
The identification and location of serious troubles
in a system may require the use of signal-tracing
equipment, such as an audio-signal generator, a meter,
or an oscilloscope. When you test the electrical circuit,
the most important point to remember is that you need to
pinpoint the location of the trouble. A careful study of
the circuit diagram is essential.
Some of the problems that cause defects in a P.A.
system are poor solder connections and loose
When checking solder
connections, make certain that both metals are
absolutely clean and that the completed soldering job is
firm and durable. Faulty soldering in a P.A. system can
cause defects that are difficult to identify and locate.
Too much solder can cause shorts in microphone
connections that may not be visible.
Mechanical connections are easy to check; just
ensure that all connections with a mechanical connector
are tight. This type of connector will be found in the rear
of the amplifier or in the console and speakers.
An interoffice communication system is used to
transmit orders and information among offices that are
only a short distance apart. Frequently, such offices are
in the same building. When an interoffice
communication system is used, you are responsible for
the installation and maintenance of the system.
An intercom system consists of two basic
configurations: the all-master system and the single-
master multiple remote system.
With the all-master system, any station can call any
other station or several stations can be connected
together for a conference.
With the single-master multiple remote system, the
single-master station can selectively call any remote
station, and any remote can call the master station.
Basically, an intercom system consists of one or
more stations, a junction box, one or more remote
speaker units, and the wire necessary to make the
The basic parts of a master station consist of a
speaker-microphone, a selector switch panel, a
combination volume control, ON/OFF switch, a pilot
light, and a listen-talk switch, all of which are mounted
in a cabinet.
The basic parts of a remote speaker unit consist of a
speaker-microphone, a push switch for signaling the
master, and a terminal board for interconnection to the
MASTER AND REMOTE STATION
You can accomplish the installation of an intercom
system easily if you follow the manufacturers
instructions and the NEC© guidelines.
Any combination of master stations and remote
stations up to the capacity of the master station can be
used. Where it is not necessary for remote stations to
communicate among themselves, you should usually
install only one master station.
Install the master station within reach of a 120-volt,
60-hertz ac power outlet. The master station and the
remote stations should be installed on the desk or in the
working spaces of the personnel who will use them. If
some of the units are to be installed outdoors, take the
necessary precautions to protect them from adverse
The size of cable to be used in making connections
between units is governed by the length of wire and the
type of system you install. The maximum wire
resistance permissible will be stated in the operating