How to fix LCD/LED TVs black screen

Ever had your TV exhibiting nothing however a black display screen even when the audio was working? Sadly, that’s a standard situation with low/middle-end LCD/LED TVs nowadays… Much more irritating, this situation usually comes from a quite tiny and low cost part that may be simply changed. Most typical points are:

• Faulty capacitor on the ability provide board
• Faulty LED within the backlight system

On this put up, we’ll check out the latter and at one option to repair it.

One among my relations had this precise symptom occurring unexpectedly. This downside on low-end TVs usually happens inside the first couple years. Because the restore prices for that sort of TV is fairly low, contemplating repairing it your self could be a good suggestion!

Prognosis

Step one into restore is to search out the foundation reason behind the difficulty. As backlight failure is a quite common situation, that is the very first thing to check. To take action, the best manner is to energy in your display screen, put a flashlight very near it and verify if you happen to can see the picture via. The picture can be very darkish, like turning the brightness of the display screen very very low.

Now that we now the picture itself is ok, this implies the primary board might be high-quality too, so we're going to check the backlight system itself.

That suggests disassembling the TV to entry the backlight which is between the LCD display screen within the entrance and the boards within the rear. In my case, with a Samsung F5000, I needed to course of as follows:

Disassembly

First we now have to take away the again housing to disclose the boards (from left to proper: foremost board, T-CON, energy provide) and disconnect the LCD panel from the T-CON board.

Flip the TV round to take away the entrance housing and the LCD panel. Be very cautious with the panel as this can be very fragile!

Now that LCD panel is eliminated, we will take away the bezel that preserve the backlight diffuser and entry the backlight itself.

Right here we will see that the backlight system is manufactured from LEDs which is fairly easy to interchange when being the reason for the failure.

Be aware: Older TVs have neon tubes for backlight, which is thicker and fewer uncovered to this sort of failure. LED backlight is the commonest factor nowadays, however don't mistake an LED TV with an OLED TV. The primary one is a basic LCD panel with a LED backlight, whereas the second is an OLED panel that doesn’t want any backlight as it's built-in in every pixels (making the spare elements way more costly by the way in which).

So, let’s take away that white cowl which is a part of the sunshine diffuser to have a superb have a look at the backlight.

As we will see, the backlight system is manufactured from 5 LED strips. Very first thing to do is search for burnt LEDs. Most LED backlight methods have strips set in sequence, that means that if one of many them fails, all of the system goes darkish…

Be aware: In the event you look carefully, you’ll see that one seems completely different than the others! third strip from the highest, sixth LED from the left. We’ll check it quickly!

Testing

Utilizing a multimeter, we will affirm that the strips are certainly set in sequence, so now we now have to check every strip individually. Professionals use LED testers resembling this one (about 40$ on amazon) however as I didn’t had one on the time, I made a decision to make one, McGyver fashion! 🤓

One LED like these ones usually wants between 2.5-3.6v enter voltage to gentle up. By wanting up this mannequin on-line, I came upon that those used on these strips want 3.6v; in order there are 9 LEDs per strip: 3.6 x 9 = 32.4v enter voltage required to gentle a single strip. That’s the utmost voltage we do NOT wish to exceed, in any other case LEDs could possibly be broken throughout testing.

So, I took Three 9v batteries that have been laying in a drawer, put them in sequence to make a digital 27v battery (Three x 9v). It’s much less then the optimum 32.4v required however not that a lot decrease, it would be capable of gentle the strip a bit so we will determine which isn't working. Here's a have a look at the set-up:

The factor with 9v batteries is that they're made to be plugged with each other! So that you simply have to put some cables on each ends and there you go.

Now we merely have to check every strips individually to see in the event that they gentle up or not. For every that doesn’t completly, it should imply it has not less than one faulty LED.

After repeating this operation on all strips, I discovered just one faulty LED, the identical we thought seemed burnt after we first had a have a look at the backlight (third strip from the highest, sixth LED from the left). For a greater understanding at what a burnt LED seems like listed below are 2 footage of a burnt one and an OK one. Thoughts the roasted colour in comparison with the common one.

Restore

Now that we now have determine what appears to be the difficulty, we now have Three choices:

• Exchange the entire strip with a brand new one
• Exchange the LED with a brand new one
• By-pass the LED and cross our fingers that the backlight will nonetheless be homogeneous sufficient

For starters I’ll go along with the third one, simply to verify there isn't any different points with the TV, however afterwards it’s higher to interchange the LED with a brand new one, in any other case you may discover a darker spot on the picture.

Often we'd like a heater to take away the LED correctly however I had none. So after just a few attempt with a hairdryer, I went messy and soldered a wire under it. 🙈

As soon as we now have by-passed the LED, we will energy the TV on. Cautious! Excessive voltage (200-300v) runs via the TV when plug, so be very cautious the way you deal with it so that you don’t electrify your self!

And Voilà! all of the backlight ought to gentle up once more.

Now we simply have to unplug the TV, exchange the LED with a brand new one and put every thing again collectively. Simply to make sure, we must always energy the TV again on and verify that every thing is ok.

Conclusion

There could be a whole lot of different root causes for comparable signs, a black display screen usually seems like one thing very critical and subsequently costly to restore, however this case is the right instance that taking a while to search for the foundation trigger can someday result in a superb shock: right here a 1$ repair!

And most of all, repairing is at all times higher than throwing away! 😊