Bias Lighting From TV Backlight Strip

Introduction: Bias Lighting From TV Backlight Strip

About: Have built my own PCs and enjoy tinkering. Also very interested in 3D printing. Using Fusion 360 to design parts to run on my Flsun i3 DIY kit.

This began with a trash picked Samsung Md55B TV..

Found the LCD screen was damaged showing only a few vertical lines when switched on.

Decided to take the set apart, to access the Power Board and other electronics.

See Step 4 for more on Bias Lighting. Other uses for LED strips: Wardrobe Lights, Work lamp, USB powered light, Cutlery Cabinet Light.

CAUTION

Make sure power is disconnected and allow the Capacitors to discharge before commencing the Disassembly.

Supplies

LED Strips from trash TV.

Any spare Power Adaptor from old Telecom device.

Solder Iron, resistor, wire.

Step 1: Very Careful DisAssembly

NOTE: Procedure below applies to this particular brand and model. Other Makes/Model may vary a little.

Place the set with the screen facing down on a flat surface or table.

Start by unscrewing all fastners on the back cover.

This will expose the electronics: Power Board, Main Board and T-Con Board in the middle (near bottom) and the two speakers.

Unplug the cable and put the speakers aside, so they do not fall off when turning set over.

Carefully unclip the ribbon cables going to the LCD screen. Then begin unclipping the bezel and retainer along the 4 sides.

Carefully turn the set over and lift off the LCD screen. Then unclip plastic strips holding the diffuser plate and reflector sheet.

This should expose the LED backlights and paper shroud. From the underside squeeze and release the plastic standoffs holding the paper shroud, and remove it to expose the LED strips.

Step 2: The LED Backlights

This particular Samsung model had just one cable from the Power Board to the Backlight Busbar.

It had 98 LEDs in 7 rows with 2 strips per row and 7 LEDs on each strip.

The were labelled Samsung 2012SV55 94V-0 Right 07 - 7 Off and Left 07x7. PN CEM-3- S E 88441.

Begin by unclip the cable from the power board and then very carefully unclip each strip and the vertical bus bar.

I then needed to investigate the voltage required to operate the Leds to determine how I could use them.

After much Google searching and close examination of the PCB copper tracks, it appeared that they were all in series. It did not make sense as it meant there was only less than 1V drop across each LED.
I needed to remove the diffuser lens covering each LED to look at the tracks more closely. It appears the lens is glued on the 3 pads.

Step 3: Breadboard Tests and Trials

Since online searches were not very successful in finding more details, I decided to do some breadboard tests.

Having many spare power adaptors from old mobile phone and telecommunication equipment, I selected a 12V Adaptor for testing.

First I scraped away small pads on the positive and negative tracks for each Led. (See the 3D model pictorial view.) Note the polarity marked on the Led strips.

Applied voltage across 3 , 4 and then 5 LEDS. and found that the maximum possible was 4 LEDs, with the 12V adaptor. This means that the LEDs require approx. 3V to operate.

Other Makes or models could be slightly different, and will need to tested as described above.

Step 4: Application As Bias Lighting for TV

While doing various Google searches to get details on the LEDs, stumbled on this article on Bias TV lighting.

See the attached link for more details.

https://www.digitaltrends.com/home-theater/bias-li...

It was an excellent use for the LED strips.

I had to trial different value resistors in series to achieve maximum light output. Approx 100 ohms gave the best light output. To be absolutely sure use Ohms Law. V = I * R/

Just need to solder positive at one end and connect the resistor in series on the -ve end.

The strip can just be fixed to the back of the TV with double sided tape, or if needed place in an enclosure with a diffuser cover.

It may need a bit of trial and adjustment to find the best position.

Other uses as in the introduction, will need a simple portable enclosure with diffuser plate.

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