Cheap LCD TV Gets Cheaper Fix

Most hacks need some fair bit of skill and knowledge if you want to come out successful at the other end. Others, you just plunge in blindly with a “heck, it’s already broken so I can’t make it any worse” attitude. Throwing caution to the wind, you dive in, rip things up, and see if you can manage to catch the bull by the horns.

[Jim]’s cheap LCD TV, barely a few years old, died. It was purchased from the store whose blue polo-shirted cashiers can drive you nuts with their incessant questions. [Jim] just rolled up his sleeves and rather haphazardly managed to fix his TV while adding an extra feature along the way.

His initial check confirmed that the LCD panel worked. Using a flashlight, he could see that the panel was displaying video which meant it was the backlight that wasn’t working. Opening up the TV, he located the LED driver board whose output turned out to be zero volts. [Jim] happened to have a lot of WS2812B strips lying around, along with their power supplies and RGB color controllers. The obvious solution was to ditch the existing LEDs and power supply and use the WS2812B strips.

Surprisingly, the original backlight consisted of just 21 LEDs arranged in three rows. He ripped those out, put in the WS2812B strips, and taped the jumble of wires out of sight. After putting it back together, [Jim] was happy to see it worked, although the new strips were not as bright as the old ones, causing some uneven light bands. He solved this by adding a few more strips of LEDs. It took him a couple of hours to fix his TV, but by the end of it, he had a TV whose backlight could be adjusted to any color using the external color controllers — although we’re not too sure what good that would be.

34 thoughts on “Cheap LCD TV Gets Cheaper Fix

  1. What I usually do after performing the flashlight test or testing the power supply board is simply googling the part number on the faulty board and a few hits always pop up. so I’m typically spending as little 20£ on a replacement inverter board because the part is old stock. LCD-tvs are incredible easy to fix when it is either the inverter or main PSU that’s gone, which in most cases it is, Buying a sufficient bright LED strip and driver is not much cheaper, if at all.

    1. The thing you already have is always cheaper than the thing you need to buy. Especially if you don’t have any planned purpose for such part. But yes, I agree that it would have made the repair easier.

      Unfortunately there’s always risk of said part having a design flaw, in this case it’s only a matter of time until the replacement part goes bad too. Early LG/Samsung LCD monitors had a very high rate of failure for the power supply. In this case getting a replacement power supply from the same time would just mean fixing the problem for a couple of months. In this case replacing the caps that failed with better caps was a much better alternative.

      And I’m not sure that displaying everything in R, G or B is exactly an improvement over a white back-light/tone. This may not count as a feature..

      1. I have a 32″ sharp LCD in my bedroom they used really cheap and nasty CapXon capacitors in the PSU eventually they turned bad and I opened it up for a look spotting brown rust stuff coming out of the capacitor’s I changed them for some cheap ones I had lying around and the fix worked. I then ordered some better quality Nichicon high temperature (105C) branded ones and I never had a problem since.
        It is always worth a go fixing something that is already broken not much to lose. I got lucky and it was a capacitor fix, So long as the screen is intact you are normally always better off buying replacements or replacing faulty components. I would have gone for a new PSU but because of the capacitor choice of the manufacturer I choose what I thought would be best a component level fix.

    2. I salvaged a really nice Soyo 24″ display 1920×1200. It had bad power supply and a bad diode, common problem with these monitors. I ended up ripping them out, checked specs, made a custom 5v and 24v power supply using laptop power supply brick (24v source). Being outside, the 24v brick dumps heat outside rather than inside, and 5v doesn’t add much heat. Still working 10 years later, not bad for a freebie dumpster dive and $20 in parts

  2. This gives ideas. Take a monitor, change the backlight to a real WS2811 stripes. Connect controller to USB.

    Then comes the tricky part. Write plugin to X which finds the position of pointer and increase the backlight under it. Using only red channel, you get perfect night vision display.

  3. If watching in bed at night you could dial back the blues and keep the reds. There are numerous articles about the unnatural blue light of mobile phone screens making it harder to fall asleep at night.

  4. There are some intriguing possibilities since you’re playing with both color addition and color subtraction. The LCD image is made by turning on and off filtered dots of RGB intended for white light, and the light is now any color you choose. So if the backlight is blue and the foreground image dot is blue, you get light, if it’s red you get black. A truly devious tinkerer (with a tolerance for seizure-level flickering) could do some interesting things by timing the background light/image frames in unusual ways.

  5. My computer monitor is a Sony Bravia KDL-40NX713 (TV tuner ripped out ready to send to OFCOM/TV licencing as proof I don’t watch TV… AT ALL).

    I got the screen from the scrapped items pile as a “sinage display”. It was written off as the thing Quote: Clicked and won’t boot. Sounds like a safety concern as it will go bang.Un-quote.

    I asked to take it home… £0.20p pack of resistors form Maplins (UK Radioshak equivalent) and it worked.

    The Mainboard pulls the normally low BACKLIGHT_EN signal high, but the voltage devider on the BACKLIGHT_EN was missing the pull-up side voltage (and thus bulled too low to see the signal). Found a 9v source after a regulator and soldered a pullup.

  6. Pretty much I had to add extra strips to my Samsung 52″ LCD TV. My situation is that I replaced CCFLs instead of LED lights. I had to go pretty much 24 strips to align with 24 CCFLs. I tossed the CCFL drivers and added an LCD power source and rewired all the connections. The only problem I see in what I did is that the light boxes are different from a CCFL based unit to an LED based unit. Namely in the depth of the box. LEDs need to either be closer to the diffusing acrylic sheets or you need more of them to avoid the banding. I will say that it turned out successful, even thought it does look a little Frankenstein-ish.

  7. Props for actually *troubleshooting* the unit (vs. taking a random board out and tossing it in the oven to “reflow” it – which seems to be a trend here). Actually had one dufus neighbor actually stuff his entire non-working computer monitor in an oven to try and fix it (“like-on-the-internet”)…. “SMH”….

  8. A 20 cent capacitor would have probably been all it took to fix the LED driver board, which is hand built anyway so should be hand fixable, unlike the logic board. My guess is that 100v cap on the right hand side. Just say’n.

    1. That’s exactly what I did with my Vizio 47″ TV. It took two capacitors for each high voltage power supply (it has two), and I was back in business. I happened to have some high quality replacement electrolytics in my junk box.

      1. Sure. But when implement this the natural color coordinates more near to yellowish white is almost impossible to achieve, I suppose. In other words, you can’t get a correlated color temperature as you want, due to the limited bandwidth of the colors used (a white, with just 3 spikes to adjust the entire light band), because the black body light is a bit different than the rainbow colours. At least, that makes sense to me.

  9. Looking at the photo album, the LED power comes off the main PSU. I’d worry that the *rest* of the PSU would break soon, but considering these LED’s were basically a $0 fix (the LED’s were dumpster-dove from Christmas!), might as well wait…

    Also, anyone else think stores ordering non-LED christmas lights these days are nuts/delusional?

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