LG 47LB570V Backlight problems after replacing LEDs

[sickboy]

Ok I despair!
I've just spent the last hour or so replacing 5 faulty LEDs in an LG 47LB570V.

When I got the TV in a few days ago the backlights were flashing on and off roughly every second. So I stripped the screen down tonight and found 5 faulty LEDs. That's the most I've ever found to be faulty in one TV.
Anyway I replaced them with the correct 6V replacements. Tested each circuit and they all lit correctly. I've built the TV back together (slit my hand open in the process and got blood all over the diffuser...) and the backlight is still flashing.

I can get a board off ebay for around £28 but I'd rather fix the original if I can.
Any tips in narrowing the fault down?

The board is eax65423801 (2.2)

[budm]

Re: LG 47LB570V Backlight problems after replacing LEDs

How many LED's are there total?

[sickboy]

Re: LG 47LB570V Backlight problems after replacing LEDs

It's all back together at the moment but I'm sure there were 4 rows of 9 LEDs, so 36 in total.

[neilc6]

Re: LG 47LB570V Backlight problems after replacing LEDs

Did you test the tv with the panel off? The TV should turn on without the panel connected to verify all the leds are functional. Sounds like you still have a faulty LED or bad connection somewhere.

[William1967]

Re: LG 47LB570V Backlight problems after replacing LEDs

With a LG television of that age the best thing to do is change all the led strips in stead of replacing a few leds. A lot of times another led goes defect and you must open the display again. Another problem is the lens wich is difficult to place back the correct way.

[Unspun01]

Re: LG 47LB570V Backlight problems after replacing LEDs

A lot of times another led goes defect and you must open the display again.

That's good advice, but hard to know if the new strips are any better because many LED strips are scavenged from parts TVs by re-sellers... They may work, but for how long?

I repaired a 50" Hisense LED LCD TV with 1 bad LED. Normally, I would just replace the 1 bad LED but I had full set of good LED strips from a spare parts TV so I replaced the 1 entire bad strip because it was quicker and easier.

I used the TV for 2 weeks then it went out again. So I opened the TV and had to replace a different strip.

Then a month later one more strip went out so I replaced that one.

In retrospect, it would have been better to replace all of the strips in that TV at the same time with the newer/better ones from my parts TV, because the original ones in that TV were just little ticking bombs...

[Unspun01]

Re: LG 47LB570V Backlight problems after replacing LEDs

Oh, and by the way 5 LEDs isn't bad for a 47"...

I had a 46" Samsung LED LCD TV with 18 out of 44 bad LEDs (burned or shorted.)

My personal record is a RCA 39" LED TV with 30 out of 30 bad LEDs shorted out... Not one single LED was still working in the TV. Not a single one. I have never seen such a thing.

I've been on the hunt for a good backlight cracked screen donor TV for over 2 years now...lol

[Unspun01]

Re: LG 47LB570V Backlight problems after replacing LEDs

Double-check your wiring connectors and check that everything is plugged in properly.

If you said each strip lights properly then your repair may be ok, but flicking on and off means you may have an open point somewhere, and the Overvoltage Protection is tripping.

[neilc6]

Re: LG 47LB570V Backlight problems after replacing LEDs

I have found that Samsungs tend to have a higher percentage of bad LEDs since the driving circuit does not shut down unlike in LG TVs. Typically they will need a full replacement since the owner keeps running the tv as it gets dimmer and may crank up the backlight level. With LG TVs, there are usually only a few out so I only replace those but make sure the owner set the backlight level to 50-60% to make sure the remaining ones last. You need to check all inputs and all smart apps. Out of dozens of repaired backlights, I've had 2 come back with a second LED failure. Also one RCA before I knew I could turn down the backlight in the service menu.

[sickboy]

Re: LG 47LB570V Backlight problems after replacing LEDs

Thank you for all the help and advice guys. I opened the screen again and found that one of my replacements had failed. Set is now working but has really obvious rings around some of the LEDs, not all of them and not the ones I replaced either. One of them is quite blue so I think more failures are imminent..
I'll have to ask the previous owner if these rings were present before the backlights failed.

You know that feeling you get when you can say YAY I FIXED IT! Then you slowly realise it's a piece of crap? lol

[Unspun01]

Re: LG 47LB570V Backlight problems after replacing LEDs

It's funny you mention the blue color of the LEDs... definitely a sign of hard driven LED and that one will probably be the next one to go.

See this thread about another 50" Samsung owner who is experiencing "rings" and some blue LEDs...

https://www.badcaps.net/forum/showthread.php?t=75154

Your LED lenses may be damaged from hot running LEDs.

[budm]

Re: LG 47LB570V Backlight problems after replacing LEDs

I found the article from one of the LED manufacturer talking about Phosphor degradation due to heat.

[sickboy]

Re: LG 47LB570V Backlight problems after replacing LEDs

It's funny you mention the blue color of the LEDs... definitely a sign of hard driven LED and that one will probably be the next one to go.

See this thread about another 50" Samsung owner who is experiencing "rings" and some blue LEDs...

https://www.badcaps.net/forum/showthread.php?t=75154

Your LED lenses may be damaged from hot running LEDs.

Yeah mine is similar to but maybe not quite as bad. The menu setting for the backlight was set to 100... I've now set it to 60 and it's still quite a bright picture at that. It will be ok for use with a games console or something, but it's no use as a main TV in a living room.

I thought LEDs were supposed to be super long lasting, it's only 4 years old. I still have a 9 year old Toshiba TV with CCFL backlight and it's in excellent working order, never had a problem with backlights. Do you think the LEDs are engineered to have a limited life?

[budm]

Re: LG 47LB570V Backlight problems after replacing LEDs

The TV manufacturers drive the LED at the max spec or beyond with disregard to thermal management.
LG Innotek the LED maker itself also warns about their LED's
※ Operating the LED beyond the listed maximum ratings may affect device reliability and cause permanent damage.
These or any other conditions beyond those indicated under recommended operating conditions are not implied.
The exposure to the absolute maximum rated conditions may affect device reliability.
※ The LEDs are not designed to be driven in reverse bias.
BTW, make sure to turn down backlights level on ALL inputs mode.

[Unspun01]

Re: LG 47LB570V Backlight problems after replacing LEDs

I thought LEDs were supposed to be super long lasting, it's only 4 years old. I still have a 9 year old Toshiba TV with CCFL backlight and it's in excellent working order, never had a problem with backlights. Do you think the LEDs are engineered to have a limited life?

Yes, LEDs are very energy efficient, and can last 30 years... Just look at regular dome shaped red, green, or yellow LEDs used in old electrical equipment (consumer or commercial grade) from 1970s until today... They are a marvel of reliability. They run cool, and rarely fail.

Now look at surface mount shit LEDs put out by TV manufacturers in the last 6-8 years. To get the high brightness useful as a TV backlight, they could use twice as many LEDs and drive them at low currents (and therefore less heat). But some asshat decided they could save money by reducing the overall number of LEDs and driving them harder to achieve the same effect...

So uninformed consumers fall for bad marketing telling us that LEDs are efficient and will last forever, when in fact they are the scourge of TVs and old CCFL and CRT technology will probably outlast all the LED tvs out there...