How to test a diode
Diodes are one of the components that can be tested very easily.Ordinary diodes as wells as Zener diodes can be checked by using a multimeter. While testing a diode the forward conducting mode and reverse blocking mode has to be tested separately.

Testing ordinary diode using a digital multimeter.
To check an ordinary silicon diode using a digital multimeter, put the multimeter selector switch in the diode check mode. Connect the positive lead of multimeter to the anode and negative lead to cathode of the diode. If multimeter displays a voltage between 0.6 to 0.7, we can assume that the diode is healthy. This is the test for checking the forward conduction mode of diode. The displayed value is actually the potential barrier of the silicon diode and its value ranges from 0.6 to 0.7 volts depending on the temperature.

Now connect the positive lead of multimeter to the cathode and negative lead to the anode. If the multimeter shows an infinite reading (over range), we can assume that the diode is healthy. This is the test for checking the reverse blocking mode of the diode.

For testing Germanium diodes, the procedure is same but the display will be between 0.25 to 0.3 V to indicate a healthy condition in the forward biased mode. The potential barrier for Germanium diode is between 0.25 and 0.3V.When reverse biased the multimeter will show an infinite reading (over range) to indicate healthy condition.
Testing ordinary diode using analog multimeter.
To check an ordinary Silicon diode using an analogue multimeter, put the multimeter selector switch in a low resistance position (say 1K).Connect the positive lead of multimeter to anode of the diode and negative lead of multimeter to cathode of the diode. If meter shows a low resistance reading, we can assume that the diode is healthy. This is the test for checking forward biased mode of the diode.

Now put the multimeter selector switch in a high resistance position (say 100K).Connect the positive lead of multimeter to cathode of the diode and negative lead to anode of the diode. If the meter shows an infinite reading, we can assume that the diode is healthy. This is the test for checking the reverse blocking mode of the diode. The meter shows infinite or very high resistance reading because a reverse biased diode has a very high resistance (usually in the range of hundreds of K Ohms).

Testing Zener diode.
The forward characteristics of a Zener diode is similar to an ordinary diode.So the methods used for testing forward conducting mode of any ordinary diode is applicable to the Zener diode too.But in reverse mode, the reverse breakdown voltage has great significance and it has to be specifically tested.For example a 5.3V Zener diode must start conducting only when the applied reverse voltage just exceeds 5.3V.The reverse bias mode of Zener diode can be easily tested by using the circuit given below.The resistance R1 can be typically 100Ohms.The multimeter must be in voltage mode.Now slowly increase the output of variable power supply and at the same time observe the voltage shown in the multimeter. The multimeter display increases along with the increase in power supply voltage until the breakdown voltage. Beyond that the multimeter reading stays put despite of the power supply voltage. This is because the Zener diode is now in breakdown region and the voltage across it will remain constant irrespective of the increase in supply voltage and this constant voltage will be equal to the breakdown voltage. If the reading of multimeter in this instant is equal to the breakdown voltage specified by the manufacturer, we can assume that the Zener diode is healthy.

While carrying out this test, remember not to exceed the input excitation voltage to a point that forces the Zener diode to dissipate more power than it can safely handle. Typically current through the diode should not be allowed to exceed more than 10mA.

How To Check Capacitor - Electronic Repair
Read On To Learn How To Check A Capacitor
If you want to know if a capacitor is defective or not then you need to know how to check capacitors using a multimeter, in this lens you will learn the correct way to do this and the equipment you will need to do the job.

Equipment Needed To Check Capacitor
To perform a check on a capacitor whilst it is still in circuit you will need an ESR meter or if you are planning on removing the capacitor from the circuit then you can get away with just using a multi-meter as an ohm-meter to test the capacitor.

To find out if your capacitor is running at the correct micro farad then you will need to purchase a capacitor tester.

What You Need To Do To Check A Capacitor Assuming that you have already removed the capacitor from the circuit board you then need to make sure that the capacitor has been discharged as they carry a charge, the easiest way to do this on a relatively small capacitor is to use a 12v automotive bulb and touch the ground of the capacitor to the case of the bulb and the power pin to the contact point of the bulb, this will dissipate the charge and then you can safely check the capacitor with your multimeter.

To use a capacitor tester you need to select the correct micro-farad setting to use, if your capacitor says 680 micro-farad then set the tester to the higher range usually 2000 mf, once you have done this just attach the black probe lead to the ground on the capacitor and the red probe to the power, you should then get a reading of the exact micro-farad which you can compare to what is written on the side of the capacitor. Don't worry i have provided some useful videos further down the page to make it abit clearer for you.

To use a multimeter
To use a multimeter to check your capacitor is working effectively you need to set the meter to the high ranges 10k - 1m and connect the probes in the same way as the capacitor tester, black to ground red to power, as soon as the probes make contact the meter should swing near zero then slowly move toward infinity before coming to a rest at infinite ohms as the capacitor is being charged by the battery in the multimeter. If the capacitor is bad then the meter will go to zero ohms and remain there, if this is the case then this is known as a shortened capacitor.
In the case of an open capacitor there will be no ohm reading and some capacitors have a dielectric leakage, you will know this if the ohm-meter comes to a rest at a point before infinity but please check this against a known working capacitor.


what do you set the multimeter
In most cases you CAN'T use a multimeter to test a capacitor. At least, you can't measure the cap's value, but you can tell if the cap has a short.

A GOOD CAPACITOR will measure a very HIGH resistance on ALL ranges.

However, if the capacitor is SHORTED (a common problem) then the OHMETER function can be used to check it.

If the capacitor is SHORTED then the ohmeter will read 0 (zero) ohms.

It is also possible for a capacitor to have a HIGH RESISTANCE short. So check the capacitor using several different ohmeter ranges. A high resistance short will measure open ciruit on the low ohm ranges, and medium resistance on the high ohm ranges.

Very high value capacitor (like 100,000 uF) will show interesting results. When the ohmeter is first attached they will show zero ohms, but then the meter will slowly climb up to very high resistence readings. This is normal for very high capacitance values.

BTW: Watch the polarity on electrolytic caps. Always connect + to + and - to -

Other than the above, you need a special Capacitance Check Meter.