No backlight on TV

Captain Jack

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My mum has brought me a knackered Toshiba LCD TV - 40L3451DB - for me to either fix it or bin it. Symptoms are sound OK but no picture.

Shining a bright torch onto the display reveals that the picture is actually there but is extremely dim - no backlight. Googling around suggests that it's a relatively common issue - with the problem being poor connections to the backlight strip. How lucky would I be if that's actually the case....

Anyone have any experience with this? @Vipersan ?
 

Captain Jack

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Took it apart and found that some of the LEDs have blown on various strips. Some are short circuit, others are open. I suspect one LED's failure led to others to burn out (it's all in series). New strips ain't cheap but if I get a working TV out of it, it'll be worth it.
 

jeallen01

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FWIW, had a similar but slightly different issue, but on a much smaller scale with one of our old Dell 1525 laptops - turned out it was the inverter, and I got a replacement on eBay for <£7, not an easy replacement job but it's been working fine for 4 years since then.
 

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I have some LED back lighting strips from some old Samsung 46" LCD TV's, they are setup in 4 groups of 16 each, each strip is about 22.5 inches long by 5/16 inch wide, I dont have the tools to remove them from the backing strips.

These things are very very very bright, I tried one out and almost blinded myself, they came on a aluminum heat-sink plate that is 23 x 9.5 inches, I have removed the strips from the heat-sink, would they work?

LED strip 1B.jpg LED strip 1C.jpg
 

jeallen01

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Generic LED strips might have different light temperature characteristics to the OEM fit units in the TV, and that might mean that the resultant backlight colours might not be "normal".
 

Terryl

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These are direclty out of a Samsung LCD/LED back lit HDTV, so they are not generic, but may or may-not be a direct replacement, I've seen the same type setups on others, and the LED's look the same, and took the same voltage.

And the same problem happened to these TV's, the LED strips would over heat and loose connection to the power supply, they never used any heat-sink compound between the LED stips and the aluminum heat-sink, it was just a dry contact.

The later models had compound between the two.

I can't get any closer to the LED's for a good look see.

Does your LED driver board look like this one???

LED driver board 1B.jpg
 

Captain Jack

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Fixed it! The new LED strips did indeed resolve the issue. Better sell it quick before something else dies on it - especially after my loitering around inside it!

2017-10-30 10.04.17.jpg
2017-10-30 12.02.07.jpg
 

2cvbloke

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Looks like a good job there, the LEDs will probably outlast the rest of the TV now... :-rofl2
 

Captain Jack

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Looks like a good job there, the LEDs will probably outlast the rest of the TV now... :-rofl2
I doubt it - these lights only lasted 3 years, albeit on a "high" backlight setting. It's not a great TV - sound is asthmatic and picture quality is very difficult to get rid. SD quality is awful... HD is just about passable.
 

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I bet that was actually a Vestel inside.
 

Captain Jack

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Dunno but the picture wasn't brilliant to put it mildly.
 

2cvbloke

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One useful thing about LED backlit TVs is you can convert them into big worklights, remove the LCD panel, strip out the electronics, get a constant current LED power supply, add a switch, and there you go... :)

I did just that earlier this year with the neighbour's old 50" TV that had been smashed, had to use two power supplies as they split the LED banks into two, but it works nice and is really bright, just need to work out where to use it... :-rofl2
 

Captain Jack

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Trust

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Some time ago I replaced the broken round fluorescent lamp from my bench magnifying-glass into 2 copper wires with sevaral leds between .
Realy cool , no longer my nose above that hot fluorescent lamp .
 

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