Modular Units

packaged functional assembly of wired electronic

can compensate quickly for the efficiency of the horn

components for use with other such assemblies. A

being greater than the cone's (fig. 4-18, view C).

modular assembly is constructed with standardized

Suppose you want to get as much power out of a horn

as the cone is delivering, and the cone is tied to the 5-watt

units or modules. An equipment that consists of

replaceable assemblies (any type) is said to be of

tap of its transformer. Tying the horn to the 1-watt tap

unitized construction. Modular construction is a type of

of its transformer would take into account the 5:1

unitized construction that consists of modular

efficiency ratio. Now you can make the horn twice as

loud as the cone by stepping up its tapped position to the

assemblies.

2-watt level.

For example, think of a carton of cigarettes. If each

There is a limit to how many speakers you can tie

pack were a module, the carton would be an equipment

of modular construction. Notice that the packs can be

across the line in this system, a limit that holds for the

arranged differently without changing the outside

transformerless matched system as well. The total load

dimensions of the carton. Although the cigarette packs

on the system by all the speaker transformers and the

are all the same size, the assemblies in many pieces of

speakers should not exceed the total power capacity of

equipment are not.

the amplifier. In the transformer system, you find the

limit by adding the rating capacities of the transformers.

By their original concept, many modular assemblies

In the matched-impedance system, you must measure

were not to be maintained in the field. The intention was

the voltage across voltages to power values, then add

to replace a faulty assembly and ship it to a repair

them up.

facility. As assemblies became more complex, the point

On a constant-voltage line, what do you do with a

was reached where the supply system required for the

transformer that is marked in impedance with no

replacement was too costly. Many of the original

mention of power? Using the formula,

modules were potted to discourage maintenance

personnel from tampering with the insides.

When the Navy reassessed this concept and called

for shipboard maintenance of as much equipment as

possible, most manufacturers began to make

convert the primary impedance of the transformer to

components accessible. However, it is difficult to dispel

power. As an example, suppose the transformer has a

the conviction that modular assemblies are impossible

primary marked 167 ohms and a secondary marked 8

to repair. This conviction may stem from a lack of

ohms. How much power does this transformer take from

experience in working with the printed circuits and the

the 70.7-volt line for its 8-ohm speaker load?

other components in modular assemblies. It is true that

Solution:

special tools and techniques are required. It is also true

that satisfactory repairs can be made to any printed

circuit by using a little care and common sense. With a

little experience, repairs can be made as easily as in

conventional assemblies, and often more easily because

of improved accessibility.

MODULAR UNITS

REPAIR OF DEFECTIVE COMPONENTS

The demand for small, maintainable circuitry in

military equipment has led to many different

One of the time-consuming steps of troubleshooting

construction techniques. One of the most popular is

is the identification of specific components. In

modular construction. Since modular assemblies

conventionally wired equipment, components are not

incorporate several subminiaturized features not found

always easy to locate. The circuitry in the chassis can

in conventional equipment, some specialized

become confusing since related components are often

knowledge and tools are required for efficient repair and

positioned in different areas of the chassis.

maintenance.

In equipment that includes printed-circuit boards,

MAINTENANCE CONCEPT

identification of circuitry and components may be

relatively simple. This type of circuit construction

A few definitions are helpful in understanding the

allows uniform placement of components. Just a quick,

terms involved. A module is, in the electronic sense, a

once-over glance of the circuitry is often all you need to

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