LG 42ls570T

[speedypro]

This is my personal TV. It works for few minutes then the back light goes out, sound still present. Using a torch, I see the video. Restart the TV, backlight comes on then the cycle repeats but it stays on on many restarts.

Could it be a backlight strip or the board itself? Sometimes left of the screen is black. But if one backlight has failed, all should as it's in series?

[Hamie]

Re: LG 42ls570T

This TV only uses one backlight strip running down the left hand side if I remember correctly.

[Andrew F. Ali]

Re: LG 42ls570T

One of the backlight LEDs could be failing as a short. therefore the strip would remain lighting but will pull a little more current (amps) and will shut down the Driver. Leaving the rest of the circuits running with no backlight.

[speedypro]

Re: LG 42ls570T

This TV only uses one backlight strip running down the left hand side if I remember correctly.

Yes, when a section looks dark, now I see why.

One of the backlight LEDs could be failing as a short. therefore the strip would remain lighting but will pull a little more current (amps) and will shut down the Driver. Leaving the rest of the circuits running with no backlight.

Thanks for that. I hope to find it as if I power off/on the tv, it works as normal but after few minutes, its gone again. I'll order few leds and replace all. Thanks.

What is the voltage for these leds? 5v/6v?

[Sucher]

Re: LG 42ls570T

One of the backlight LEDs could be failing as a short. therefore the strip would remain lighting but will pull a little more current (amps) and will shut down the Driver. Leaving the rest of the circuits running with no backlight.

Thats not like that really. The current in the whole circuit stays the same, as its a series connection. This particular LED bar consists of 6 circuits ( loops) with 6 feedbacks to Dimming controller( AUO K301-29 chip). If one led diode goes short theres higher voltage drop across that diode which in turns leads to higher voltage voltage supply of this loop, the chip senses that and shuts down the entire supply. If the diode goes 'short' it doesnt mean its resistance is zero( like a shorted transistor) the diode wont light up, the current in this circuit is the same but its resistance will increase. However if you removed that diode snd put the solder blob on it( to shorten it) the led driver would inteligently reduce the drive voltage to match it with the numbers of leds in this circuit. This is PWM supply- not purely DC, the amount of current is controlled by PWM pulses.

Paul