Using Digital Multimeters
One test which is simple that you are able to perform on a power cord is checking the output voltages. This reveals whether a power cord is operating properly and whether the output voltages are in the appropriate tolerance range. Remember that you have to measure each voltages with the power cord attached to a good load, which often means testing as the power cord is still installed in the device and attached to peripheral devices and the motherboard.
Picking out a Meter
You have to have an easy electronic multimeter (DMM) and electronic volt ohm meter (DVOM) to do voltage and also resistance checks on electric circuits (see Figure 17.39). Only have a DMM rather than the old needle type multimeters because the earlier meters function by injecting 9V into the circuit when computing resistance, which damages very computer circuits.
A DMM uses a significantly lower voltage (usually 1.5V) when making resistance measurements, that is safe for electronic equipment. You are able to get a great DMM with numerous features from many sources. I choose the small, pocket size meters for computer work since they’re not hard to take with you.
A number of options to search for in an excellent DMM are as follows:
Pocket size – This’s self explanatory, but small meters with numerous, if not every, of the functions of larger ones can be found. The intricate features found on several of the bigger meters aren’t actually needed for computer work.
Overload protection – In case you plug the meter right into a voltage or even present outside of the meter’s capability to measure, the meter protects itself from harm. Cheaper meters lack the protection and also may be quickly harmed by reading present or maybe voltage values which are too much.
Autoranging – The meter automatically selects the appropriate resistance or voltage range when creating measurements. This’s desirable to the mechanical range selection; however, great meters provide both autoranging capability along with a mechanical range override.
Detachable probe leads – The leads may be damaged very easily, and quite often an assortment of differently shaped probes are needed for various tests. Cheaper meters hold the leads forever attached, which implies you cannot easily replace them. Search for a meter with removable leads which plug in to the meter.
Audible continuity test – Even though you are able to utilize the ohm scale for testing continuity (zero ohms indicates continuity), a continuity test feature can cause the meter to develop a beep sound when continuity exists between the meter test leads. By utilizing the sound, you easily can test other items and cable assemblies for continuity. Once you have this feature, you won’t ever need to make use of the ohms display for this function once again.
Instant power off – These meters run on electric batteries, moreover the batteries can effortlessly be worn down when the meter is unintentionally left on. The best multimeters for computer repair provide an instant shutoff which turns away from the device when it senses no readings for a predetermined time.
Instant display hold – This function allows you to keep the final stable reading on the screen even with the reading is considered. This’s particularly beneficial in case you’re attempting to work in a difficult-to-reach area single handedly.
Bare minimum and maximum trap – This feature allows the meter to capture the highest and lowest readings in mind and keep them for later screen, and that is particularly beneficial in case you’ve readings that’re fluctuating too rapidly to find out on the screen.
Even though you are able to buy a simple pocket DMM for just twenty dolars, one with each one of these functions is priced closer to hundred dolars, and many may get so much higher.