To check the LED and find out its parameters, you need to have in your arsenal a multimeter, "Tsashka" or a universal tester. Let's learn how to use them.
Continuous ringing of individual LEDs
Let's start with a simple one, how to ring an LED with a multimeter. Switch the tester to the transistor test mode - Hfe and insert the LED into the connector, as in the picture below.
How to check if the LED is working? Insert the anode of the LED into the C connector of the zone marked PNP, and the cathode into E. In PNP connectors, C is the plus, and E in the NPN is the negative terminal. Do you see the glow? This means that the LED check is completed, if not, the polarity is wrong or the diode is defective.
The connector for testing transistors looks different, often it is a blue circle with holes, so it will be if you check the LED with a DT830 multimeter, as in the photo below.
Now how to check an LED with a multimeter in diode test mode. First, take a look at the verification diagram.
The diode test mode is indicated by a graphical image of a diode, more about the designations in. This method is suitable not only for LEDs with legs, but also for testing smd LEDs.
Checking the LEDs with a tester in the dial mode – shown in the figure below, and you can also see one of the types of connector for testing transistors described in the previous method. Write in the comments about what kind of tester you have and ask questions!
This method is worse, a bright glow of the diode appears from the tester, and in this case - a barely noticeable red glow.
Now pay attention to how to test the LED with a tester with anode detection function. The principle is the same, with the correct polarity, the LED will light up.
Infrared diode test
Indeed, almost every home has such an LED. They are widely used in remote controls. Let's imagine a situation that the remote control stops switching channels, you have already cleaned all the keyboard contacts and replaced the batteries, but it still does not work. So you need to watch the diode. How to check the IR LED?
The human eye does not see infrared radiation, in which the remote control transmits information to the TV, but it is seen by your phone camera. Such LEDs are used in night illumination of video surveillance cameras. Turn on the phone camera and press any button on the remote control - if it is working properly, you should see flickering.
Methods for checking an IR LED with a multimeter and a conventional one are the same. Another way to test an infrared LED for serviceability is to solder a red LED parallel to it. It will serve as a visual indicator of the operation of the IR diode. If it flickers, then signals are being sent to the diode and you need to change the IR diode. If the red does not flicker, then the signal is not received and the point is in the remote control itself, and not in the diode.
In the control circuit from the remote control there is another important element that receives radiation - a photocell. How to check the photocell with a multimeter? Switch on resistance measurement mode. When light hits the photocell, the state of its conductivity changes, then its resistance also changes downward. Observe this effect and see if it is in good condition or broken.
Checking the diode on the board
How to check an LED with a multimeter without unsoldering? In the principles of its verification, everything remains the same, but the methods change. It is convenient to check LEDs without soldering with probes.
Standard probes will not fit into the transistor connector, Hfe mode. But sewing needles, a piece of cable (twisted pair) or individual veins from a multicore cable will fit into it. In general, any thin conductor. If you solder it to a probe or foil PCB and connect the probes without plugs, you get such an adapter.
Now you can ring the LEDs with the multimeter on the board.
How to check the LEDs in a flashlight? Unscrew the lens unit or the front glass on the lamp, carefully unsolder the board from the battery pack if the length of the conductors does not allow it to be freely viewed and examined.
How to ring an LED lamp?
Any electrician has called an incandescent lamp many times, but how to check an ICE lamp with a tester?
To do this, you need to remove the diffuser, usually it is glued. To separate it from the body, you need a pick, or a plastic card, which must be tucked between the body and the diffuser.
If you cannot do this, try to warm up the gluing place a little with a hairdryer.
Now how to check the LED light bulb with a multimeter? Before you will be a board with LEDs, you need to touch the tester probes to their terminals. Such SMDs in diode test mode light up dim (but not always). One more way to check the serviceability is to make a continuity check from a battery of the "crown" type.
Krona gives out a voltage of 9-12V, so check the diodes short sliding touches to their poles. If the LED does not light up with the correct polarity, it needs to be replaced.
LED spotlight check
First, take a look at what LED is installed in the spotlight, if you see one yellow square, as in the photo below, then you will not be able to check it with a tester, the voltage of such light sources is high - 10-30 Volts or more.
You can check the performance of an LED of this type using a known good driver for the appropriate current and voltage.
If there are many small SMDs installed, checking such a spotlight with a multimeter is possible. First you need to disassemble it. In the case, you will find a driver, waterproof pads and a board with LED. The construction and testing process is similar to the LED lamp described above.
How to test an LED strip for performance
On our site there is a whole article about how we will consider express verification methods here.
I must say right away that it will not be possible to illuminate it entirely with a multimeter; in some situations, only a slight glow in the Hfe mode is possible. First, you can test each diode separately, in diode test mode.
Secondly, sometimes it is not the diodes that burn out, but the current-carrying parts. To check this, you need to put the tester in the dial mode and touch each power lead at different ends of the tested area. This will identify the whole part of the tape and the damaged one.
The red and blue lines highlight the strips that should ring from the very beginning to the end of the LED strip.
How to test an LED strip with a battery? The power supply of the tape is 12 volts. You can use a car battery, but it is large and not always on hand. Therefore, a 12V battery will come to the rescue. Used in radio doorbells and control panels. It can be used as a power source when calling problem areas of the LED strip.
Other ways to check
Let's see how to check the LED with a battery. We need a battery from the motherboard - CR2032 size. The voltage across it is about 3 volts, sufficient to test most LEDs.
Another option is to use a 4.5 or 9V battery, then you need to use a resistance of 75 ohms in the first case and 150-200 ohms in the second. Although from 4.5 volts, checking the LED is possible without a resistor with a short touch. The margin of safety LED will forgive you for this.
Determining the characteristics of diodes
Assemble the simplest circuit for characterizing an LED. It is so simple that you can do it without using a soldering iron.
Let's first look at how to find out with a multimeter how many volts our LED is using such a probe. To do this, carefully follow the instructions:
- Assemble the diagram. In the open circuit (on the “mA” diagram) set the multimeter in the current measurement mode.
- Move the potentiometer to the maximum resistance position. Reduce it smoothly, watch the diode glow and the current increase.
- Find out the rated current: As soon as the increase in brightness stops, pay attention to the reading of the ammeter. This is usually in the order of 20mA for 3, 5 and 10 mm LEDs. After the diode reaches the rated current, the brightness of the glow remains almost unchanged.
- Find out the voltage of the LED: connect a voltmeter to the LED terminals. If you have one measuring device, then exclude the ammeter from it and connect the tester in the voltage measurement mode in parallel to the diode into the circuit.
- Connect the power supply, take the voltage reading (see connection "V" in the diagram). Now you know how many volts your LED is.
- How to find out the power of an LED with a multimeter using this circuit? You have already taken all the readings to determine the power, you just need to multiply the milliamps by Volts, and you will get the power expressed in milliwatts.
However, it is extremely difficult to determine the change in brightness by eye and bring the LED to the nominal mode, you need to have a lot of experience. Let's simplify the process.
Tables to help
To reduce the likelihood of a diode burning out, determine by its appearance which type of LED it looks like. For this there are reference books and comparison tables, focus on the reference rated current when conducting the characterization process.
If you see that at the nominal value it clearly does not give out the full luminous flux, try exceeding the current for a short time and see if the brightness continues to rise as quickly as the current. Watch the heating of the LED. If you applied too much power, the diode will begin to heat up intensely. Conditionally normal will be the temperature at which you cannot hold your hand on the diode, but when you touch it, it does not leave a burn (70-75 ° C).
To understand the causes and consequences of doing this procedure, read.
After all the work done, check yourself again - compare the readings of the devices with the table values of the LEDs, select the nearest ones that are suitable in terms of parameters and correct the resistance of the circuit. This is how you are guaranteed to determine the voltage, current and wattage of the LED.
A 9V crown battery or a 12V battery is suitable as a power supply for the circuit, in addition, you will determine the total resistance for connecting the LED to such a power source - measure the resistances of the resistor and potentiometer in this position.
It is very simple to check the diode, but in practice there are different situations, so many questions arise, especially for beginners. An experienced electronics technician will, in appearance, determine the parameters of most LEDs, and in some cases, their serviceability.
