LED TV backlight repair no back returns

[Davi.p]

Hi, sometimes i changed single broken leds, but happened that after sold the tv the defect came back maybe with another led, how to avoid theese returns? I thought a longer testing at full brightness but how much long? Thanks..

[neilc6]

Re: LED TV backlight repair no back returns

I only do LED replacements when new strips are not available or too expensive and turn down the backlight to as low as possible around 50%. Usually Insignia, Haier or RCA models.

For LGs (LN, LA, LB, LF. UJ-turns blue) and Samsungs (E, F, H, J model years), I do full replacements with new strips since they are usually available and usually not too expensive. Also turn down the backlight as well.

https://www.badcaps.net/forum/showthread.php?t=90775

[Davi.p]

Re: LED TV backlight repair no back returns

Ah yes i know there is a modify for each led driver to hard modify the brightness. I think there aren't other solutions.. Thanks.

[angelos]

Re: LED TV backlight repair no back returns

Yes Davi,
I go through the pain of changing all LED's manually using a hot plate and other tools. This is done because in my country there is no supplier of LED strips leaving me to import them from China. The chinese do a manual repair on the old strips so if they can do it and charge me $25 plus shipping then i can also repair them. The other issue is the shipping cost with aliexpress now charging $42 to ship with UPS, DHL etc.

That said, i repair the LED strips and then drop the current on the driver board from 300mA to around 180 to 150mA. Brightness is only slightly compromised.
I cannot do this with LG LED strips since these strips are glued on and once i removed them them have shape like banana and never glue down on the board.

The sets i repair are mostly the cheap chinese units. If you know how to reduce current great but if you want to know how to do it i am willing to tell you on this thread. Interested?

[vinceroger69]

Re: LED TV backlight repair no back returns

The sets i repair are mostly the cheap chinese units. If you know how to reduce current great but if you want to know how to do it i am willing to tell you on this thread. Interested?

could you please let us know how you reduce the current im certainly interested im sure other members will be too.

[Davi.p]

Re: LED TV backlight repair no back returns

I have already seen how to reduce current in some models by desoldering a resistor. Not so much difficult.. thanks.

[Davi.p]

Re: LED TV backlight repair no back returns

Maybe a good idea is to cover the led tub with a heavy blanket to accelerate the process of aging of the defective leds during tests..

[angelos]

Re: LED TV backlight repair no back returns

Yes, on those all in one board type TV's if you look carefully around the plug feeding the led strips you will see a parallel resistor network. Sometimes they are 0.47 Ohm in parallel with another 0.47 ohm in parallel with another resistor. You might even see that there is place on the pcb tracks for another resistor but it was left intentionally blank. Anyway you remove one resistor at a time while monitoring your current draw.

You can do this on LG TV's and most chinese models. I have had little success on Sony, JVC and Samsung. Their circuit is slightly different and i do not want to damage anything

[Davi.p]

Re: LED TV backlight repair no back returns

Thanks...

[gabiz_ro]

Re: LED TV backlight repair no back returns

On led only replacement.
Set your bench power supply on CC and depending on led forward voltage to some higher value.Test each led and compare result.
At last if possible power entire strip from bench power supply and increase voltage until leds start to shine check if all looks the same.

So set bench power supply to 400mA and voltage at 7-8V and test each led.
Just doing this now,really,most of leds I see on display show 3.8V at 400mA.
One led dead,0mA,no light.
One led 70-80mA and no light.
One blinking led,few mA no light, 400mA and light then few mA and no light and cycle repeats.
So I need to replace 3 leds

Also you may find that many leds show you 3.6V as example and one or few show 4V or even 4.2V those need to be replaced also.


At last step,powering entire strip,that one in work now is 11 leds,connected to power and increasing voltage leds start to light at around 26.5V and all light identical so seems OK,but if one or many doesn't light the same or no light I need to replace them too.

As for reducing current you may search for datasheets and if available there is specified how current is set and see what you need to modify to result desired current.

All of the example was considering 3V leds,in case of 6V leds adjust to required values.

[Davi.p]

Re: LED TV backlight repair no back returns

Hey gabiz thanks! It seem a very interesting guide, i'm only surprising that inputting 7-8v 400mA on a 3V good led doesn't damage it.. I will put in practice this wonderful guide!

[gabiz_ro]

Re: LED TV backlight repair no back returns

No damage.
7-8V when no load,when something is connected voltage drop to some value and current limited to 400mA.

Let say you short output,depending on cables you may get 0.04V and 400mA even you set 8V output voltage or apply voltage to one 4.7 ohm resistor,current will be limited to 400mA and voltage will drop to 1.8V