Digital and Analog Multimeters

What is a Multimeter?

• Multimeter is a combination of different kind of testing meters including an ammeter, ohmmeter and voltmeter which helps to detect the correct operation or failure of various types of components.
• Multimeter consists of an analog or digital display, 2 probes and a selector switch.
• Multimeters are used to measure resistance, amperes and voltages.
• Beginners should prefer auto-ranging digital multimeters than buying analog multimeters for safety purposes.

How to use a multimeter safely?

1. Multimeters should not be used over maximum voltages mentioned in the multimeter.
2. Filter capacitors in power supplies should be discharged before testing.
3. Disconnect the input power before making resistance or diode test.
4. Don’t attempt to repair or service the multimeter.
5. Don’t touch the metal probes , while testing for currents and voltages.
6. Always turn off the power and disconnect the probes before replacing the batteries or fuse in multimeters.

A computer will not switch ON, If there is a faulty switch, blown power supply or a bad power cable.

How to test a computer power supply using multimeters?

• ATX power supplies won’t work unless it is connected to the motherboard. You must insert the metal probes into the backside of the connector to make contact with the wires.
• Use the power supply’s pin diagram to identify the different testing locations. Usually power is carried through pins 1,2,4,6,9,10,11,19 and 20.
• Set the multimeter to DC voltage and range to 20 Volts.
• Insert the black metal probe into the back of the connector with any black wire and insert the red metal probe into the back of pin 12. Multimeter should display voltages between 11 or 12 volts. Also test the pin 10. If the voltage is too low or high, power should be replaced as it is failing.
• Also test the pins 4,8,9,19 and 20  for 5 volts.
• Also test the pins 1, 2 and 11 for 3.3 Volts.

How to check the ON/OFF switch in computers?

• Unplug the PC’s power cable.
• In ATX ON/OFF switches, either 2 wires or 4 wires are used.
• Connect multimeter probes to 2 wires of the ON/OFF switch, and press the ON/OFF button to view the drop in resistance. If the resistance drops  to near zero, the switch is working. No need to replace.
• Note, before pressing the start button, multimeter shows infinite resistance. In digital multimeters, i indicates infinite resistance.

How to test a BIOS battery in computers?

• Unplug the computer’s power cable from wall outlet.
• Press and hold the ON/OFF button for 5 seconds to drain the residual power from the motherboard.

• Set the multimeter to DC voltage. Place the multimeter’s black lead to the negative terminal of CMOS battery and red probe to the positive side. Crosscheck with the CMOS battery’s voltage rating.

How to test the motherboard components?

Logic probes are used by experts to check the motherboard components. But multimeters can only be used to check the voltage, current and resistance of the motherboard components, if required. 

As shown in the above image, Fluke is the topmost brand in multimeters. Also have a look at the blow multimeters from triplett and get one now to measure.

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