Mulja tv repair portal
Equipment Repairs => LCD TV forum => Topic started by: Turnip on March 26, 2017,08:38:54
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Hi folks,
Just got a Sharp LC32LD145K with sound but no backlight. Notice backlight uses just a pair of leads so guess all strips in series, although that represents rather a lot of volts
Checked voltage from 17IPS19-5 reading 25v where surprisingly the Black lead was positive. Tried a string tester and at 20m/a got a max reading of 17.5v.
Suspect a huge number of S/C diodes - Chris.
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The LED driver board isn't behind the screen by any chance? I was 'foxed' once, the two wires carried about 24V DC for the board.... I expected a third wire for the PWM brightness control, mind you it wasn't a Sharp, thought I'd just mention.
Dave
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Thanks Dave,
Thought take it apart finding two series strings of 11 Leds with the first Led on each string S/C.
Curious thing, when I then connected the 'String Tester' all but the duff pair lit up. Odd as I'd checked the voltage from 17IPS19-5 (25v) and also with the string tester when disconnected from supply (17.5v) - Bit odd, might well have a supply issue if it can suss just two duff diodes out of 22.
Next problem is that the strips are really well stuck down, and lenses pop off when I try lift, even with a certain amount of hairdryer heat.
Tend to suspect flexing also liable to offend the good diodes - Maybe rip strips out and replace all diodes.
At 10p per genuine LG diode - £2.20 is cheaper than £46 for a new pair of strips - Much more fun too if you have the time - Chris.
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Thanks Dave,
Thought take it apart finding two series strings of 11 Leds with the first Led on each string S/C.
Curious thing, when I then connected the 'String Tester' all but the duff pair lit up. Odd as I'd checked the voltage from 17IPS19-5 (25v) and also with the string tester when disconnected from supply (17.5v) - Bit odd, might well have a supply issue if it can suss just two duff diodes out of 22.
Next problem is that the strips are really well stuck down, and lenses pop off when I try lift, even with a certain amount of hairdryer heat.
Tend to suspect flexing also liable to offend the good diodes - Maybe rip strips out and replace all diodes.
At 10p per genuine LG diode - £2.20 is cheaper than £46 for a new pair of strips - Much more fun too if you have the time - Chris.
Have you got a link to genuine lg leds at that price or is it just through trade etc
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Hi Vince,
Mentioned the Leds on quuq a few weeks ago. Think they're still listed as -
100-500-1000pcs-High-Power-LG-110LM-1watt-3528-LED-Backlight-Television-Backlit
Used my first new ones today and they looked far better than smashed screen Leds that may work, but seem a bit the worse for wear under magnification - Chris.
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Yes thats the ones i have ordered thanks again.
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Hi folks,
Think mention after replacing the two duff Leds - All OK.
Seems then that the 17IPS19-5 can suss two duff Leds cutting supply to a basic 25v feed.
Checked supply voltages from the menu - Max 85v Mid 78v Min 75v - Set it to Mid so it doesn't come back for a while - Chris.
Just sorted another one, one burned and S/C Led. As it's such a pain to lift the strips, thought try Bonesys idea - Crumble the top, clean the area, remove surface covering so there's enough exposed copper. Use LMP solder and an iron bit wide enough to melt both sides at the same time and watch the new Led sink into place - Much faster with this screen, but doesn't work so easily with the ones where both sides of the Led are at the same potential for heat sinking, and the feed to the next Led is in fine print.
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I tend to use a wallpaper scraper to lift the strips off of the metal frame, it requires a fair amount of force to get them up initially but prevents the lenses from popping off :)
Also noticed one seller selling those leds 300 for £11+ postage better price than buying a thousand of them! I suspect the price should be £21 so I ordered some! I will keep a few and sell the rest on ebay!
http://www.ebay.co.uk/itm/252450138118
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Hi Cheeky,
Them leds is getting cheaper all the time. Suspect time you get your spares on Ebay they'll be even cheaper.
Currently paying 10p a pop, and as usually need just two or three - Margin is pretty good, but have to allow for folks who turn the backlight up to 100% within 3 months and pop a few more.
Currently a good earner with 32 inch stuff - Chris.