How to test electronic components

Checking electronic components It is one of the fundamental tasks when a circuit does not work or when you are going to solder the component, checking that it works correctly before doing so and then having to remove the solder to replace it.

Well, here we will show you how to do it in a simple way on each electronic device with the help of a multitester or multimeter, like the ones I recommend here:

UNI-T UT890C Multimeter...

PeakTech 3441 –...

Industrial FLUKE 115 True...

I would also recommend buying some good probes with alligator clips so you can make your measurements more comfortable. In some cases you will have to manipulate other things, and you will need to free your hands. With tip probes you will have to keep your hands busy and maintain contact, which is uncomfortable. With clamps, you can have your hands free and the measurements will be even more accurate, as the tips do not move around on the terminals…

IMCCZONY Power Cable Kit...

Check conductivity (closed circuit, not open) and short circuit

These tests can be performed on both cables and printed circuit tracks, thus proving that there is continuity between the two ends, meaning that the electrical conductor is not broken or cut. To begin, you have to follow these steps:

Turn on your digital multimeter.
Turn the selector to the icon that shows a diode and buzzer symbol.
Touch both ends of the conductor you want to test with the multimeter test probes.
If the display shows 0 and the buzzer sounds, then the conductor is in good condition, not cut or broken.

Tip: Remember to keep the probe tips clean, as well as the terminals or connectors you are going to insert them into. Dirt, rust, etc., can alter the measurement values.

On the other hand, for Check for short circuits in these same conductors, that is, tracks or cables that have come into contact when they should not, then the steps to follow are these others:

Turn on the multimeter or digital multimeter.
Turn the selector to the diode and buzzer symbol.
Using the multimeter probes, touch the two tips or ends of the circuit or conductor you want to test.
If a measurement other than 0 appears on the display and the buzzer does not sound, then there may be a short circuit.

Just as tests are performed on conductors, the operation of switches or push buttons could also be tested using the same steps, seeing if acting on them closes and opens the circuit while keeping the tips in contact with the input and output terminals.

Check resistance

Now for check a resistor, then we have a very simple way to do it. The procedure to do it step by step is as follows:

Turn on your multimeter.
Select the mode to measure resistances, that is, the one with the Ohm symbol (Ω).
Now, using the test leads, you need to touch both terminals of the resistor.
If the ohm measurement on the screen matches what the resistor should be giving (remember that it won't be exact, due to tolerance, so if there are a few ohms too many or too few, that's fine), then everything is fine. Otherwise, the resistor has a problem, such as when it gives a value close to zero or too high.

If the resistor is installed in a circuit, it would be ideal to remove it to make the measurement correctly, so that nothing else interferes with the measurement of the value, although many times this is not done, and the terminals or contacts are simply touched without removing…

Check fuse

To Check if a fuse is in good condition or if it has broken, if it is not visible to the naked eye, then you can do the same as to measure the continuity of a circuit, as we did in the first section. That is, the steps would be:

Turn on your multimeter or voltmeter.
Turn the selector to the icon that shows a diode and buzzer symbol.
Using the test leads, touch both terminals of the fuse.
If the display shows a 0 and the buzzer sounds, then the fuse is in good condition. Otherwise, it will indicate that it has blown and must be replaced.

Check inductor or coil

With this test you will not only be able to Check the inductors or coils of the circuits, also those of other elements such as transformer coils. The steps in this case would be the following:

Turn on your digital multimeter.
Select the mode for measuring Henries (H), or Wb/A, which appears on the thumbwheel. On some instruments this may be indicated by an X1.
Now touch the test leads to the two conductive ends of the coil. *Make sure the probes are connected correctly to your multimeter, as some need to connect them to the connectors where an Lx appears to measure inductances.
This way, we can check on screen if the measurement is correct.

You can also test for continuity in the same way we did before, to see if the coil is broken. But remember, if there is continuity, it doesn't mean the coil is good... What is true is that if there is no continuity, then we can say that the coil is broken.

Check diode

To Check semiconductor diodes, we can follow these other steps that I show you here in a simple way:

Connect your multimeter.
Select the diode test icon, which is the same one you've been using to test circuits for continuity. It has a diode symbol on it.
With the black tip you should touch the cathode of the diode, while with the red test tip you should touch the anode of the diode. This is important. Also, in this case the black probe should be connected to the COM port of the multimeter, and the red one to the one with the symbol on it. Ω.
Now you will see the values on the screen. If the screen shows approximately 0.7v for silicon diodes, or 0.3v for germanium diodes, then it is good. Other values will indicate that the diode is not good.

Remember that you can also connect it in reverse polarization, in that case, connect the red to the cathode and the black to the anode. In this case, .1 will appear on the screen if the diode is good.

Remember, if you need to replace a diode, always do so with one of the same specification. Or, if this is not possible, one slightly higher than the original, but never lower.

You could also check LED diodes, In these cases, the steps are:

Turn on your multimeter.
Select the diode test icon, as above for conventional diodes.
In this case, the black probe should be in contact with the shorter terminal of the LED diode, while the longer one will be in contact with the red probe. Remember that in reverse polarity it will not light up.
You should now see the LED light up if it is working properly.

Finally, if you want Testing a Zener Diode, You have to do this:

Turn on your digital multimeter.
Select the diode test icon, which is the same one you've been using to test circuits for continuity. It has a diode symbol on it.
With the black tip you should touch the cathode of the diode, while with the red test tip you should touch the anode of the diode. This is important. Also, in this case the black probe should be connected to the COM port of the multimeter, and the red one to the one with the symbol on it. Ω.
In this case, it is completely different from the conventional diode. While connected directly it will provide a figure on the screen, when connected in reverse, in this case, no measurement will be obtained on the screen.

Check capacitor

To Check electrolytic capacitors Using a multimeter, the steps you need to follow are:

Turn on your multimeter.
Select the mode to measure capacities (Farads).
It is important to place the black probe on the negative terminal of the capacitor. While the red probe will go to the positive pin.
You will now be able to see on the screen whether the measurement corresponds to the capacitor specifications, as with the resistors. Remember again that due to tolerance, it may not be an exact value. On the other hand, if you see that the measurement is much lower than it should be, then it may indicate that the capacitor has lost capacity and needs to be replaced.

If you have to check a ceramic capacitor, the steps would be the same, although in this case it is not necessary to pay attention to the terminals to which you connect the probes. Any measurement below the capacity it should give or intermittent measurements will indicate a fault.

Check transistor

Check NPN or PNP bipolar transistors It's also quite simple. You just have to be clear about which pin corresponds to which part or the other. As you know, we have the emitter (E), the base (B) and the collector (C). If your multimeter has the option to test transistors, you just have to insert the pins accordingly into the circle with contacts E, B and C on your multimeter, and it will perform the tests. However, if you don't have this option on your model, we will use the diode mode:

Connect your multimeter.
Select the diode test icon.
Now, the tests we can do are:
- Base to Emitter: with the positive tip on the base of the transistor and the negative tip on the emitter. If the NPN transistor is in good condition, it should display a voltage drop of between 0.45V and 0.90V on the screen. If it is a PNP, we will see OL or Over Limit on the screen, that is, an overflow due to the value that exceeds the measurement threshold.
- Base to Collector: In this case, the positive lead will go to the base, while the negative is connected to the collector of the transistor. If the NPN is in good condition, it will show a voltage drop as in the previous case. In the PNP it will also show OL.
- Emitter to Base: For this test, the negative probe is connected to the base, and the positive probe to the emitter. In the case of a PNP in good condition, it will show 0.45V to 0.90V. In the case of an NPN, it will show OL.
- Collector to Base: Connect the negative lead of the multimeter to the base, and the positive lead to the collector. In a good PNP, it will show the same voltage drop as in the previous point. In the case of an NPN, the limit will also appear to be exceeded.
- Emitter to Collector: In this case, the negative lead goes to the emitter, the positive lead to the collector. If the transistor is in good condition, both in the NPN and PNP, the display will indicate OL.
- Collector to Emitter: We connect the negative to the collector and the positive to the emitter. In NPN and PNP transistors in good condition, OL is displayed.

In case of wanting Testing FET Transistors, such as N-channel or P-channel, we can also use our multimeter. Remember that in this case we have the source (S), gate (G) and drain (D) terminals. The steps would be:

Turn on your multimeter or multimeter.
Select the mode to check diodes.
The tests that we can perform in this case, using an N-channel MOSFET as an example (remember that for the P-channel it would be different in some cases due to the gate polarization...), are:
- Connect the positive probe to the gate and the negative probe to the drain. If the transistor is good it will not show conduction.
- Connect the positive probe to the gate and the negative probe to the source. If everything is OK, there should be no conduction either.
- With the positive tip to the drain and the negative to the source. If the MOSFET is good, it will look like there is a short circuit between these two terminals, but this is not the case…*
- We reverse the probes on the previous terminals, positive for source and negative for drain. In this case, it should also look like there is a short circuit between the terminals if everything is OK.*
- If we repeat the two previous tests, we will see that it is no longer short-circuited, the reason was that the gate was activated by the test voltage…

*When taking the measurements we made on the transistor gate, the voltage measured by the multimeter was sufficient to polarize and charge the transistor gate. And as long as the gate maintains that charge we will have conduction between the drain and source terminals. In some transistors, the gate charge can remain for quite a long time, long enough for someone without experience to think that the transistor is faulty. The solution is to make sure, before taking the measurements, that the transistor gate is discharged and to do this we can make a short circuit between the gate-drain or gate-source terminals with a conductive metal or with the tip of the multimeter itself.

Check relay

In case of wanting Check the status of a relay, you can also use your multimeter in a simple way. However, here you have to keep in mind one detail. As you know, on one side we have the NC and NO terminals, on the other the Common terminal. You also have the terminals for the relay coil. If you test these two coil terminals, to check the coil, you can do the same as for measuring coils or inductors as we said before.

Another check you can do is between terminals NO and C, or between NC and C. In the first case there should be continuity, in the second there should not be, that is, the circuit would be open. We also learned how to do this before…

Check Xtal

Last but not least, you can also try the so-called Xtal, or oscillating crystals which generate clock signals. In this case:

Turn on your multimeter.
Select the mode to measure frequencies (Hz).
Touch the Xtal terminals with the test probes.
On the screen you should get the measurements corresponding to the oscillator you are measuring. For example, if you measure an 8 Hz oscillator, you should have that measurement on the screen. If, for example, 2.5 Hz or anomalous values appear, it will indicate that it is broken.

Final Tips

To carry out the checks, I advise you Always have the component datasheets you are going to test so that you have in mind the values that you should obtain in each case, and thus compare them with those that appear on the multimeter screen. Remember to also read the manual of your multimeter, since there may be slight differences between models.

Of course, Always keep your multimeter in good condition, Avoid dust, rust or debris that can cause incorrect readings. Also, make sure other components are working properly, for example, if the buzzer is working by touching a circuit or wire that you know for sure has continuity, etc. Keep the battery in good condition, as a low battery charge could also cause incorrect readings.

If you are going to measure components soldered to circuits, without removing them, take into account the circuit. For example, there may be a circuit with traces that you make contact with to measure a resistance, but if those traces also pass through other resistors in series or parallel, it will alter the values…