Toggle switches work in several different ways.
Lets examine the three most common types
two-position; and three-position.
Alternate-action toggle switches Alternate-
action toggle switches can be permanent up and return
to neutral, or they can be permanent up or down.
Placing the switch in a permanent up position will turn
a unit on or off, activate a function, or set a parameter.
Returning the switch to the center position (neutral)
may or may not interact with the computers software.
Placing the switch in permanent up or down position
can also cause an immediate or delayed response from
the computers software.
Momentary-action/contact, two-position toggle
switches Momentary-action/contact, two-position
toggle switches are usually used to initiate an operation
or perform a function. Depressing the switch down
momentarily activates this switch, and it will then return
to a neutral position (center) when not being used.
Three-position toggle switches Three-position
toggle switches operate basically the same way as the
momentary action/contact, two-position toggle
switches except one more variable has been added.
These switches can be placed in a locked up position,
left in the center position (neutral), or in the down
position, which can be a momentary-action or locked
down position. The center position may be used to set
a parameter, or it may be used to disable the locked
Two-position switches can be left in an up or down
In either position there will an
TOPIC 2TYPES OF COMPUTER
CONTROLLING UNITS AND THEIR
We have discussed the types of controls that are
associated with controlling units. Next youll study the
different types of controlling units associated with
computers. It is important to note that not all types of
controlling units are used to control every computer.
You will not find each and every one of these controlling
units on every computer you operate and maintain.
However, some computers have a combination of two
or more of these controlling units to enable you to
operate and perform maintenance on the computer. To
show you how controls and indicators are generally
labeled on drawings, we selected several examples and
have presented them in figures. These examples point
out many of the controls and indicators used on
Learn the capabilities and limitations of each of
these controlling units to enhance your abilities to
operate and maintain any type of computer. We do not
go into a detailed discussion of these controlling units,
but rather we discuss the tasks they are capable of
You will find the operation of the
controlling units in the computers technical or owners
manual. In the operation or initial setup section of the
technical or owners manual, you will find a general
description of the controlling unit or units on your
system. It will give the operation, an illustration, and
tables and figures to describe each control and indicator
used by the computer or associated equipment.
Manuals that have a functional description section
provide all details of operation. Controlling units are
also supported by circuit diagrams (prints) that contain
information you can use to perform maintenance.
All controls and indicators are important; be
particularly aware of controls that when activated
interact with computer operations. Computer
operations include those operations that are executed by
programs/software as well as manual operations
activated when performing corrective maintenance.
The programs and software include the diagnostics used
to perform preventive maintenance as well as the
An example of a manual
operation would be a short maintenance program you
would assemble and manually load into the computer
and run to check a specific function of the computer.
Know and understand the controls and indicators
thoroughly. They are your means of monitoring
computer operations and an aid when you perform
maintenance. Detailed information of every control
and indicator will include the following:
The name of the control or indicator
Type of control or indicator
Function and use of the control or indicator
F i g u r e 3 - 2 i s a n e x a m p l e o f a
typical controlling unit for a computer.