Properly soldering leds

Soon, perhaps, workshops may appear with the sign "Solder LEDs" due to the increasing number of LED-backlit devices every day. The usual Ilyich light bulbs, which have illuminated the path to a bright future for nearly a century, are being replaced by LED lamps. The name speaks for itself: the main component in devices is the LED. Despite the progress and development of various technologies, the installation of the LED in the devices is performed using the old-fashioned soldering method. But while this niche in the business does not have its pioneers, you can try to master the repair of LED devices yourself.

The scheme of the device led strip

Diagram of the device LED strip.

Device classification

In everyday life, we have to deal mainly with three groups of devices containing LEDs and available for home repair. Despite the general method of testing, replacing or installing new diodes, each of them has its own peculiarities when checking for serviceability. If you do not take into account the differences, efforts and funds for repairs may be wasted. There are various devices:

  • self-powered;
  • mains powered;
  • motorcycles and other vehicles.
SMD LED Soldering Aid Scheme

Circuitry for soldering SMD LEDs.

Self-powered devices. This group includes flashlights of various designs, control panels, toys and everything else with a power source from batteries or rechargeable batteries. The voltage used is small and safe.

Network powered devices. This group can be included in the first place lamps with power from the outlet or through switches. It also includes all devices for charging mobile, kitchen devices, television and audio equipment, and so on. They use a voltage of 220 V, during operation it is necessary to observe precautions.

Cars, motorcycles and other vehicles. Mainly used voltage 12 - 14.5 V, it is safe for life. At such a voltage, high-power LEDs work, diodes of small and medium groups should be connected via a limiting resistance or a current stabilizer. If the connection is incorrect, the LED may be out of order.

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Using the instrument to check

LED soldering scheme

Scheme soldering LEDs.

Before replacing the LEDs, you need to make sure that the problem is in the failure of the LED, and not in another part of the circuit. The test can be performed by the device, if available, or by an improvised device. Checking the device is carried out in accordance with the instructions to the device. There are two options for verification. In the first device is set to the voltage measurement mode, the probes are connected to the LED, power is supplied and the button is pressed, when turned on, the LED should be on. If the device shows the presence of voltage, but there is no light, the element needs to be changed. In the second embodiment, the test is performed by measuring the conductivity in the forward and reverse direction.

If the device is digital, the switch is set to the diode test mode; in the resistance test mode, the device does not respond to the connected diode. The dial gauge can be checked in resistance measurement mode. The LED is similar to a diode and is checked the same way. In the absence of breakdown or breakage, the device should show a small resistance when connected in direct polarity, and much more in connection with the return polarity. If the instrument reading when changing polarity is equally small or large, the LED is faulty. The luminescence of light-emitting diodes when checking by the device can arise only on the most low-power LEDs.

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Checking homemade device

Diode wiring diagram

Diode connection scheme.

Testing can be done homemade device. The best homemade version is to use the backlight unit from a regular lighter. To do this, you must carefully remove it in the kit from the case. The unit must be in working condition. The verification method is simple, instead of an element on the unit or with it, you need to connect a diode that needs testing and close the switch contacts. If the native LED is on, but the test is not, you need to turn the last one and insert the legs in reverse. That is, change the polarity of the connection. LEDs conduct current in one direction. Close the contacts again. If the second version of the glow will not, you can throw. When testing, consider the electrical parameters of the LED being tested. The unit is designed to work with components from the group of average power, current up to 60 mA, voltage 4-5 V. When checking elements from the group of low power it is necessary in series with the LED to connect the limiting resistance.

The operation of infrared LEDs (remote controls) can be checked with a mobile phone with a camera. The phone turns on the shooting mode, the camera is sent to the LED in the remote. A button is pressed to create a signal for transmission. On the screen, the color of the diode should change, otherwise it may be faulty.

When repairing devices with a group of LEDs (flashlights, lamps, automotive lighting devices), you should pay attention to the method of connecting LEDs. Classic connections - serial and parallel. Possible combinations of groups in which several elements are connected in parallel, and the groups themselves in series. When checking a large number of LEDs located on the board, it is desirable to mark faulty elements with a felt-tip pen or a marker.

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How to solder LEDs

Connection diagram of two LED strips in one power supply

Connection diagram of two LED strips in one power supply.

A set of necessary tools and materials:

Soldering iron with a rated power of 40 W, in the absence of a more powerful with the use of nozzles.

  1. Tweezers or small platypuses, copper wire with a diameter of 1 - 1.5 mm.
  2. Side cutters or small pliers.
  3. A vice or other device for fixing the board.
  4. Toothpick or matches, you can simply wooden stick.
  5. Tin, rosin, alcohol, solvent.
  6. Acid soldering or aspirin.
  7. Device or improvised device for testing.

First, before soldering the diodes, it is necessary to disassemble the device for the most convenient access to the place of soldering of the diodes. If possible, separate the board with the LEDs from the device. To clean the surface from dust and other dirt, possible oxides, using a tampon or cloth moistened with alcohol. Conduct an external inspection and determine the status of soldered contacts. It is not uncommon for the contacts to oxidize at the soldering points or if the connection is cracked from mechanical impact on the diode case during operation.

LED device

LED device.

With these signs, it is still necessary to check the LED for good health. If the LED is in good condition, heat the damaged contact with a soldering iron until the tin melts and allow to cool. Then once again carefully inspect the place of soldering and try to slightly move the legs of the LED. The cracks or free movement of the legs indicate a poor connection. In this case, the diode should be evaporated completely, remove the oxide film from the legs, cover with a thin layer of tin (tin) and solder back.

To remove the film, apply soldering acid on the feet at the soldering points and wait 4-5 minutes. You can clean it more quickly with an aspirin tablet. You need to put the contacts on the pill and warm up with a soldering iron. Working with a soldering iron does not require much ingenuity: turn on the outlet, wait until it reaches the melting point of tin. You can determine the degree of heating by periodically trying to melt the tin. If the soldering iron is new, you should wait until it burns (stops smoking) and chew the sting. The soldering points should be warmed up by applying a soldering iron tip to them. The contact area should be as large as possible. In order to properly solder the LEDs, the power of the soldering iron for components of low and medium power should be no more than 40 watts.

If you have a soldering iron of greater power, you can wrap a copper wire with a flattened end on the sting and solder it. Defective LEDs can be soldered without any problems, without fear of overheating.

After removing the old elements, the holes must be cleaned of solder.

The clogged hole is heated and a toothpick is inserted into it. Wand can be slightly rotated. On new LEDs, if necessary, bend the findings, the element is placed in the holes. In order not to fall out, on the reverse side of the legs you can bend and trim the excess. The soldering tip needs to grab a small portion of the solder and apply it to the junction. As soon as the tin snaps the lead and the track, remove the sting and blow. Something like this you need to solder the LEDs. Solder for soldering should be used with a low melting point.

On sale there are special packaging in the form of a pencil. They contain a ready-to-use solder mix with a flux in the form of a wire. The tip of this wire should be attached to the place of soldering and heated. The risk of overheating the diode with less. Good LEDs should be protected from heat. To do this, you can use tweezers from copper wire, made by yourself. The pins of the LED must be intercepted with tweezers above the soldering point and held until the solder cools. After replacing all the elements, it is necessary to clean the places of the ration from rosin with a tampon or a cloth moistened with alcohol, to remove all excess tin. Carefully inspect the place of rations on the possibility of fusing nearby contacts and tracks.

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