Toggle  Switches Toggle switches work in several different ways. Let’s  examine  the  three  most  common  types— alternate-action; momentary-action/contact, 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 computer’s software. Placing the switch in permanent up or down position can also cause an immediate or delayed response from the computer’s 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 up/down position. Two-Position Switches Two-position switches can be left in an up or down locked position. In  either  position  there  will  an immediate response. TOPIC 2—TYPES OF COMPUTER CONTROLLING UNITS AND THEIR CONTROLS We have discussed the types of controls that are associated with controlling units. Next you’ll 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 controlling  units. 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 performing. You  will  find  the  operation  of  the controlling units in the computer’s technical or owner’s manual. In the operation or initial setup section of the technical or owner’s 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 operational programs. 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. 3-4