Alternative backlight for an LCD tv
Not too long ago I purchased a used LCD tv from eBay. The price was good at $100 for a 27″, but the backlight died within a week of use! After some research I found out that practically no one carried a replacement inverter for this model. The only alternative that I found was done on a 17″ LCD monitor using LED lights. This is where I started.
My tv is a 27″ widescreen, so I figure I need a lot of LEDs. I started with 24 and quickly tripled that. I had to drill a little hole for each LED to put in place. I protected all the contacts with heat shrink wrap and hot glue, which I also used for fixing the LEDs to the tv. Each light takes about 3.5V DC, so I strung six in serial to power it with 24V DC. These batches were put in parallel. The first attempt produced bright lines on the screen, because the LEDs are spot lights (very narrow light beam).
Next logical step was to put little pieces of reflective tape on each LED. At this point you really have to learn to be patient! Unfortunately, I did not like the result. Considering how the tv is constructed, it has 3 films that the light has to go through before hitting the actual screen (pixel matrix glass plate). This clearly wasn’t enough for the LEDs to become diffused. Here is a picture:
My second idea involved a flashlight type of approach. I wanted to use a regular light bulb and to create a cone shape in order to spread the light onto the screen. Initially I wanted to use wood for the prototype, but then I decided to make it even easier by using styrofoam. Styrofoam did not offer the rigidity, but it definitely left the tv very light! The idea is simple: make the cone shape out of styrofoam and then cover the inside with tinfoal to make it reflective.
I had to go through a number of bulbs to get the right tint too. Finally, I found a good energy saving (13 watt) light bulb that produced a good tone of white. Regular bulbs at 60 watts+ get way too hot for this model. To finish things up I used a 5VDC relay, so the bulb would work only when the tv works. Here are few shots:
For more pictures visit my Picasa Page.
Tags: alternative, backlight, LCD, LED, replacement, television, tv
April 18th, 2008 at 7:30 pm
Your idea is original but you would benefit from using screw in flourescent bulbs. They put out 60 watts while using about 12 and don’t overheat like regular bulbs do. That’s what is used, in a rectangular strip form, as the original backlight. I also have the same problem with my TV. Dell sells strip backlighting for their monitors so you should look into it. I too have been using a flashlight on the front of the TV to see images. What a pain in then rear.