LG LED backlights

Oily

Oily

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Trying to fix the backlights on my LG TV,as you can see from the photo some of the strips don't work but individually all the SMD's work apart from 5.I've rigged up a variable 3v to 12v psu to try and power the strips (and SMD's individually),some of the strips work whilst others don't even light up even though they have worked as seen in the picture?
Would one dodgy SMD stop a whole strip/s from working or is there something in the strip that could be knackered?Tried doing a continuity test on the strips but it only goes to the 1st SMD and no further?
Electronics ain't my strong point but always willing to learn.
Got some new SMD's ordered from RS which should arrive tomorrow but don't want to waste my time if the strips are knackered.
 

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The LED's are normally wired in series so, like the old Xmas tree lights, if one goes out the rest (in the same circuit) follow. Sometimes they go short circuit which means the line won't go out but it'll put extra strain on the remaining ones. I have a 42" one in just now where every one of its 32 LED's are shorted and another (47") with an intermittent o/c LED. Both LG's.
If you use (sewing) pins as probes, you might be able to check each individual LED for continuity by poking them under the lenses.
If you can wait you can get whole new strips fairly cheap from Ali Express. Not a bad idea as all your LEDs will be the same age & others may be ready to fail.
Whatever way you go, do update your software to hopefully limit the current to the strips in the future.

NB Some LG sets use 6V LED's!!
 
trevortron said:
The LED's are normally wired in series so, like the old Xmas tree lights, if one goes out the rest (in the same circuit) follow. Sometimes they go short circuit which means the line won't go out but it'll put extra strain on the remaining ones. I have a 42" one in just now where every one of its 32 LED's are shorted and another (47") with an intermittent o/c LED. Both LG's.
If you use (sewing) pins as probes, you might be able to check each individual LED for continuity by poking them under the lenses.
If you can wait you can get whole new strips fairly cheap from Ali Express. Not a bad idea as all your LEDs will be the same age & others may be ready to fail.
Whatever way you go, do update your software to hopefully limit the current to the strips in the future.

NB Some LG sets use 6V LED's!!
Click to expand...

Cheers Trevorton,if wired in series how come on some rows there's one out but all the rest are lit up?Ordered some 6v led's off RS,soldered them on and now none light up :p
All I get now is the standby light blinking 3 times then off?Not as easy as I first thought :D
 
Oily said:
Cheers Trevorton,if wired in series how come on some rows there's one out but all the rest are lit up?Ordered some 6v led's off RS,soldered them on and now none light up :p
All I get now is the standby light blinking 3 times then off?Not as easy as I first thought :D
Click to expand...

It sounds like the one that's out was short-circuit therefore passing current through to the rest. Re. flashing standby light- check (a) that the originals are 6V and not 3V LED's, and also that you soldered them in the right way round. The flashing standby is probably indicating that the set has gone into protection mode which they sometimes do if the backlight load is radically different to what it should be - i.e. open or short-circuit. Or maybe you forgot to plug something back in?
Google it with the model number, might tell you more.
 
trevortron said:
It sounds like the one that's out was short-circuit therefore passing current through to the rest. Re. flashing standby light- check (a) that the originals are 6V and not 3V LED's, and also that you soldered them in the right way round. The flashing standby is probably indicating that the set has gone into protection mode which they sometimes do if the backlight load is radically different to what it should be - i.e. open or short-circuit. Or maybe you forgot to plug something back in?
Google it with the model number, might tell you more.
Click to expand...

Thanks Trevrton,googled the blinking lights and it appears to be a hardware issue?All the repair ads I've seen are selling 6V smd's so I've just gone with those and they're all soldered the right way :p
 
@Oily, looking at your wee video, you have 9 LED's per strip. That's the same as my 4 year-old LG 47" 47LN575S. I've just checked my notes and it definitely has 3V LED's. I'm going to open it up again, as I replaced the dead LED with a 'warm white' one I had in the drawer. And it's quite obvious, particularly on dark scenes.
 
trevortron said:
@Oily, looking at your wee video, you have 9 LED's per strip. That's the same as my 4 year-old LG 47" 47LN575S. I've just checked my notes and it definitely has 3V LED's. I'm going to open it up again, as I replaced the dead LED with a 'warm white' one I had in the drawer. And it's quite obvious, particularly on dark scenes.
Click to expand...

Bugger! Most if not all sellers on ebay are selling 6v so assumed this was the norm.How much difference will a few 6v smd's make?These ones I've got are cool white ,4000K
 
How many is "a few"? Each one you changed allows the voltage to rise by 3V above what it's supposed to be and this may be detected as a fault.
Mine has two rails with 27 led's (3 strips) per rail, so roughly 100V per rail. 3 or 4 6V LED's on one rail would allow that rail to rise by 10V or more, quite enough to trigger a fault condition.
FWIW 15000-20000K is 'cool white' temp, 4K might be a bit on the yellow side. see Original For LG LED TV Strip Bar Repair , 100pcs 3528 2835 3V SMD Lamp Beads | eBay
 
These leds' generate a lot of heat. I haven't encountered it personally yet but have seen images of severe burn-ups supplied by other engineers. It's one thing for a diyer to swap out caps in the LT supplies but for most everything else it can be downright dangerous for bodged repairs by the untrained.
Some of your comments Oily leave me in no doubt that you should have took your tv to your local repairman. Personally I wouldn't even look at a repair that's been attempted, finding introduced faults to get to the original problem
 
trevortron said:
How many is "a few"? Each one you changed allows the voltage to rise by 3V above what it's supposed to be and this may be detected as a fault.
Mine has two rails with 27 led's (3 strips) per rail, so roughly 100V per rail. 3 or 4 6V LED's on one rail would allow that rail to rise by 10V or more, quite enough to trigger a fault condition.
FWIW 15000-20000K is 'cool white' temp, 4K might be a bit on the yellow side. see Original For LG LED TV Strip Bar Repair , 100pcs 3528 2835 3V SMD Lamp Beads | eBay
Click to expand...
I've changed 8 trevorton,most are single ones on each strip with the exception of one where i changed 2
 
Oily said:
I've changed 8 trevorton,most are single ones on each strip with the exception of one where i changed 2
Click to expand...
chookey said:
These leds' generate a lot of heat. I haven't encountered it personally yet but have seen images of severe burn-ups supplied by other engineers. It's one thing for a diyer to swap out caps in the LT supplies but for most everything else it can be downright dangerous for bodged repairs by the untrained.
Some of your comments Oily leave me in no doubt that you should have took your tv to your local repairman. Personally I wouldn't even look at a repair that's been attempted, finding introduced faults to get to the original problem
Click to expand...

Not a stranger to changing caps etc trevorton,fixed my Onkyo amp and made my own PSU for my VU+ Duo ;)
 
Forgot to mention this tv was given to me as a project as the guy was binning it,so not wanting to spend big money on it,Ordered some off the link you posted trevorton so we shall wait and see
 
Yeah, I get a few of those- sometimes the only ones worth spending much time on. That's how I cam across the 47"-er.
 
Only downside is some of the diffusers that I glued back on are a little off centre on the smd's I soldered on causing different light variations across the screen.
I can put up with them for now,can't grumble at a free 47" LG smart tv that's cost less than a tenner to fix :D:cool:
 
Hey guys. I hope I'm.not intruding, I have an lg 47" the picture flashes on and off, when I lower the the brightness and put it into Eco mode it sometimes stableisess. Could it be the power board? Any advise would be apreciated. Thank you

-

Sent from my MotoG3 using Tapatalk
 
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