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LG 42LS575T intermittent backlight issue
dynomoman:
Hello,
Having an issue with an LG 42LS575T that has an intermittent backlight problem. This model has a separate LED driver board.
The set seems to run ok for a few hours. Turn off and next day it wont always come on. I get sound with no picture. Shine a torch at the screen and I see the LCD is working ok, just backlight dropped out. I tried freeze and heat treatment but it shows nothing
Has anyone seen this issue before on this set ?
Thank you!
downunder:
Hi Dyno,
Time to strip the display panel and check the LED strips, after you check that BL-ON (INV-ON) signal is present when it fails, as well as a substantial voltage present on the connector on the LED driver board supplying the LEDs plus 24V supply to the LED driver.
LED backlights are essentially a "bad technology" and they're falling over like flies. One bad LED results in no LEDs at all due to protection circuits. A common cause of grief is that the LED strips often have a joiner near halfway on each strip. These sometimes develop a bad connection or high resistance. You may also find signs of overheating around a bad LED. Remember that the LEDs on each strip are in series.
Could ramble on for hours about LED backlighting, so see how you go.
Bruce
dynomoman:
Thanks for the info Bruce.
If this set is like my LG 47 inch version the LED s are along one edge. I had to take my main tv a 47 inch LG panel apart due to a bad LED strip which I found was a track had shorted on the strip and went open circuit. A manufacturing defect by the looks of it.I manage to repair that one ok, but it's not a job for the faint hearted for sure.
This 42 inch i am working on runs ok for days at a time then fails to light the backlight. I am not 100% it's the LED S but it could be. I will carry out some checks as you suggest. I agree running these LED S so bright with all that heat must really punish them.
I have read on the net that my model of tv has quite a lot of issues with the back light going intermittent . But no info as to why sadly.
Regards
Mike
downunder:
If repairs are successful, it's a good idea to turn the "backlight" setting in the menu down to 50% so that the LEDs aren't being driven at full bore. Currently working on a Sony that is top and bottom lit by about 280 LEDs. Wouldn't you know it, every one of them lit when checked with a DMM in diode mode. Back to the drawing board.
Bruce
dynomoman:
Not sure if this is of any use to anyone but I found these on Aliexpress today. Looks like replacement LED strips like the ones in the video on you tube. Sadly mine are rectangle close together types.
http://www.aliexpress.com/item/2pcs-x-Original-32-inch-LED-Strips-w-Optical-Lens-Fliter-Large-Size-TV-Panel-Backlight/32571400469.html?spm=2114.031010208.3.96.jKLUsX&s=p&ws_ab_test=searchweb201556_1,searchweb201644_5_79_78_77_82_80_62_81,searchweb201560_6,searchweb1451318400_6148
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