TV Backlight Issue

To answer this, we need to understand a little about how a TV makes its image

A TV makes a self-luminous image. A flat panel TV makes this image using one of two basic ways, commonly known as OLED and LCD. Confusingly, both types use LEDs to make the light for the image, and some LCD displays are called LED displays. We will concentrate on the LCD displays and let the OLED types go.

The LCD display uses white LED backlights to provide light that the LCD matrix then modulates. The liquid crystal (hence the LC of LCD) in this display is formed into tiny pixels or dots. These have electronically controlled color filters that regulate the color and brightness of the light.

But the starting place is the backlight—no backlight—no image.

• Many backlights in TVs with an LCD have strips of multiple LEDs behind the LCD. (there are TVs that have LEDs around the edge of the screen.)
• The LEDs on these strips have lenses which serve to spread ot the light they produce.
• Generally the backlight circuit with these LED strips is fed a constant current at whatever voltage is needed.
  • Brightness is increased by increasing the level of the constant current (which causes more heat to be generated in the LEDs).

Heat is the leading cause of backlight failure. What fails and the consequences of the failure can vary.

The failure of one LED on a strip might create a slightly dim area on the screen. When a more serious failure occurs, such as multiple LEDs failing and becoming short circuits, the power supply will shut down because it will overheat.

If an LED fails as an open circuit, then the entire backlight will usually stop working.

LEDs are arranged differently on different TVs so that some failures may affect a specific TV differently. You can test the strips to find out what has failed.

Heat is the great enemy of virtually all electronic components and backlights are no exception. More heat—more failures.

Keeping the brightness turned up constantly, especially to 100%, will increase failures in the LEDs from heat generation. This is the single worst thing you can do to your TV. Also, TV’s that are on 24/7 are more prone to failure because of long term heating.

Over time, components like resistors, capacitors, and diodes on the strip will degrade because of the heat produced by the LEDs. When they fail, they frequently damage the LED strip irreparably, such as causing burnt areas on it.

Associated with the heat failures mentioned above, the lenses that spread the light from each LED can fall off. This is usually caused by excessive heat, which melts the adhesive holding them to the strip. This will cause a bright spot on the screen instead of a darker area.

The lenses can be reglued in place. This process requires a means to perfectly place the lens to reglue it, or the light will not be spread evenly. A new strip (or strips) may be a better choice.

1. Backlight failures usually cause dark areas, which are most noticeable when the image is dark because you will see a darker spot on the screen. The lit portions will bleed through light, but where the LEDs are not working, the screen will be darker.
2. Lens Failures will cause bright spots while the area remains lit, although perhaps a bit dimmed.
3. Edge-lit TVs aren’t as common, and failures in those units often show up as a dark half-screen.
4. If the screen will not light at all in any portion:
   1. you may have a power supply failure (uncommon), or
   2. you may have a sufficient number of failed LEDs or other components on the strips that the power supply shuts down.

Many backlight failures are repairable. Once the damaged component is identified, it can be replaced.

If the backlights or anything on the backlight strips are the problem, replace ALL the backlights, especially if there is more than one failure. Backlight strip kits cost around $30-60US, which is considerably less than a new TV.  It’s kind of like headlights on a car, if one burns out, the other one will probably follow soon. So do them all.

Follow this Samsung Television Backlight Replacement guide for more details.

Here is a good video by a reputable author with some valuable diagnostic information