Mulja tv repair portal
Equipment Repairs => LCD TV forum => Topic started by: Turnip on March 01, 2018,10:37:07
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Hi folks,
Got a Toshiba 40BL702B in where expecting to replace duff Vestel Leds find it's a Sammy screen with edge lit leds.
Screen is LTA400HM13 - Famed for failure.
Wonder if there's a best way to attack it - Chris.
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Hi Chris,
With much care. LEDs are very close to the edge and raised a bit, I think. Easy to knock off in disassembly. Did just that, but with a bit of
aussie ingenuity was able to short one LED out without upsetting the current sensors. Generally unrepairable. Bruce
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Hi Bruce,
Thanks for the 'heads up' - Got screen apart without incident finding two Led strips with two Leds duff on one of the four sections.
Guess the next bit is the problem as strips are glued to the aluminium heat sink so have to be removed to get any heat on the back of the strip so can lift duff Leds off and resolder new ones.
Wonder if the glue used is something like 'hot melt' as don't want to try prise the strips off as will wreck them - Chris.
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All a bit iffey, Chris. Guess they were made not to be repaired. As a last resort you may be able to wiggle faulty LEDs and break them away. This will expose the tiny pads, but getting another LED in may be a challenge. Good luck with it. Bruce
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Thanks Bruce,
Chap who supplied new Leds suggested 'Hot Melt' to secure them, but didn't mention how to release strips, so suspect a bit of heat the biz.
Might try with a paint stripper, but first think try with my Henly Solon 60 Watt soldering iron clipped to the heat sink sink might do both release and resoldering.
Have a Henly Solon 125 watt iron, but usually use it for sorting seized grease in antique motor ball joints, clipped with a 'G-cramp' for half a day - Seems to work, most times - Chris.
Later - Heated heat sink with 125 watt but Leds wouldn't shift. However, heat enabled me to prise the strip out, and with the iron underneath, Leds could be lifted off strip no problem. Replacing was interesting as thought solder paste might be the biz - It wasn't as the new Led floated about the strip then dropped off due to the heat. Next tried using LMP solder dabbed on the five pads and a drop of liquid flux to ensure soldering. Worked a dream, the Leds didn't shift, soldering looked perfect and the string functioned. Just wondering what to stick it back in with - Could use double sided tape as original but not sure of holding qualities with the stuff I can get, and it's important with maybe 40 watts of heat to dissipate to the heat sink.
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Maybe something like this
http://bit.ly/2DKzqTo
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No Paypal. You have to pay by credit card, but I have dealt with Aliexpress before and they've been OK so far. It's a long wait though,
Bruce
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Hi folks,
Got my tape Ebay - uktape232 - 6mm x 25m at £1.35 inc post. seems ideal. Noticed that heat from the Leds had caused the filters to corrugate a bit at the top, but screen and set now functions.
Now, had they put the Leds at the bottom, they would have cooked the integrated screen drive panel and flexies as well. Feel Edge lit screens great for monitors and small stuff, but back lit more sensible for anything bigger as heat is dissipated over the whole back panel (Unless its plastic where it catches fire) - Chris.
Perhaps if the Leds were arranged both sides, might be better, though would cost.
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Hi Chris'
Agree with you about the heat generated. I accidentally placed my hand on one through the week and was horrified at the heat level.
Bruce
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Would the crinkles not cause anomaly in casting shadows etc and don't they use infra red activated glues?
Dave
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Hi Davy, you've got me there, knowing nothing about IR glues.
Picture seems pretty even top to bottom though I did forget the order of the various sheets - Recall there were three to do something or other, and possibly replaced them in the correct order, though don't know if it's significant.
Worst bit was static electricity, where the more I wiped off extraneous crap, the more it flew in - Fun, so ordered 50 more Leds from China as guess there will be a lot more, and next time I will label the sheets - Chris.
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I try to keep the sheets sandwiched between two dustbin liners, my way of thinking is they will grab particles better than the filters due to the static charge. It's a real pain keeping the dust and hairs out.... you can't see the devil but when it lands on the filters it can be quite noticeable.
Remember well, unpacking a Hoover auto washing machine from the box..... I yanked the plastic bag it was wrapped in and got one hell of a belt, ya could have lit a city with the charge.
I'll stand to be corrected, the most mottled or denser sheet goes on the bottom and mistier ones at the top.
You could try the old grammy phone antistatic brush or cloth if they must be wiped, I did wipe one once with a very lightly moist lint free cloth and seemed to turn out OK after letting it dry a few minutes.
Dave
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Denser sheet on bottom as you say as the top ones have 'lugs' to go on plastic surround
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I try to remove them as one sheet, all together, but just in case I scrawl numbers on the plastic tabs before I remove them. Apparently the order is significant. It's when you attempt to clean them that you get all confused. Bruce