Lab 10.1: Using a Multimeter

A multimeter is an invaluable tool when it comes to ensuring that the correct voltages are being passed to a device or computer. It helps you determine whether the problems you may be experiencing are the result of faulty power or a faulty device. If the proper voltages are not being delivered, the devices cannot function properly.

You can also use a multimeter to perform continuity checks on cables. A continuity check gives you a quick indication of whether a wire is broken. If you get a reading of 0 ohms, the wire is good. If the reading is infinite, there is a break in the cable. The same check can be performed on a fuse to see if it is still good.

Upon completion of this lab, you will be able to:

• Use a multimeter to measure DC voltages

• Use a multimeter to perform a continuity check

Set Up

For this lab, you will need the following:

• A working computer

• A multimeter with leads

• An IDE cable

Exercises

A multimeter is a very useful tool to help you identify the voltages that are being provided to your computer and peripheral devices.

Measuring DC Voltage on a Molex Connector

To measure DC voltage on a Molex connector,

1. Prepare the multimeter for use. If the multimeter has detachable leads, connect the black lead to the negative jack and the red lead to the positive jack on the multimeter. Set the multimeter to measure DC voltages. Set the meter to read for voltages less than 20VDC.

2. Turn off the computer and unplug it.

3. Remove the system cover.

4. Locate a Molex power connector. It will have two black wires, one red wire, and one yellow wire. The black wires are ground wires. You will determine the voltage carried on the red and yellow wires.

5. Connect the black multimeter lead to one of the black wires and the red multimeter lead to the red wire.

6. Plug in the computer and turn on the power. Observe the voltage reading and record it:

   Red wire voltage:

7. Turn off the computer and unplug it.

8. Leave the black multimeter lead connected to a black wire. Move the red multimeter lead to the yellow wire.

9. Plug in the computer and turn on the power. Observe the voltage reading and record it:

   Yellow wire voltage:

10. Turn off the computer and unplug it.

Measuring Continuity

To measure continuity,

1. If you have an extra IDE cable, you can use it; otherwise remove an IDE cable from your computer. Note the location of pin 1 on both the IDE controller on the motherboard and on the IDE devices.

2. Change the setting on the multimeter to read Ohms.

3. Place one lead on one end of pin 1 and the other lead at the other end of pin 1. Record the reading:

   Pin 1 reading:

4. If you removed the IDE cable, replace it in the computer. Take care to ensure that pin 1 is connected to pin 1 on the IDE controller on the motherboard and to the pin 1 on the IDE device.