LG Flashing Backlights

[provider10]

Hi All

Got this LG 32LN5130 . The red standby led flashes 3 times then the backlighs flash on for a fraction of a second. Then it repeats the sequence. Have stripped it down and find all LEDs are good. (tested with LED checker)

Also if i unplug lead from main board, LEDs do not come on.

Can anybody help

Thanks

James

[yokoono]

Re: LG Flashing Backlights

1. The backlight ignition motherboard disconnect test is valid for Samsung not LG.
2. Even if the LEDs light up with the tester, the test is not conclusive. You have LEDs with increased consumption.
3. Replace the LED strips, reduce the current through them and solve the problem for several years.
4. Measure if, when the backlight goes out, there is still voltage on the BL-ON pin (3-5V).
5. You can force the backlink by putting a + (3-5v) on the BL-ON pin. You can take the voltage through a 1Kohm resistor from the stb pin.

[alfatv]

Re: LG Flashing Backlights

Take a video of LEDs turning on/off. Then go frame by frame and find where LEDs are turning off. See if there is one single LED going off before others.
Do this with panel removed.

Also, without replacing LED strips, you can do steps 4-5 described above by yokoono.
You can find service manual at electrotanya.
There are 2 pins,"power on " and "DRV on". Not sure which one will turn on LEDs. Try 1K from 3.5V to each of these separately or use two 1K's to both.

[budm]

Re: LG Flashing Backlights

Can we also see the pictures of the whole backside of the TV showing all the boards?

[provider10]

Re: LG Flashing Backlights

HI thanks for the replies

I take it that drv-on is bl-on

When the lights flash on and its only for a fraction of a second, the pwr-on and the drv-on
voltages drops. I attached 3 volts to the bl-on and the lights come on but are flickering

I then put a 39 ohm resistor in series with the lights and they stayed on

[provider10]

Re: LG Flashing Backlights

On further exploration i fitted a diode 1N5822 in series and the lights stay on . So it looks as if one of the LEDs is faulty. Yet they all light up and all give the same brightness

[budm]

Re: LG Flashing Backlights

I am not surprised if it has bad LED/LEDs on these LN series.

[provider10]

Re: LG Flashing Backlights

Wilke i had the lights on I noticed that one of the heat sinks on the PSU was getting very hot. checking around I found D104 was SC. replaced it and all lights are now on without the diode

Thanks

[angelos]

Re: LG Flashing Backlights

Wilke i had the lights on I noticed that one of the heat sinks on the PSU was getting very hot. checking around I found D104 was SC. replaced it and all lights are now on without the diode

Thanks

Could we get a picture of the faulty diode in the mother board for future reference?

[provider10]

Re: LG Flashing Backlights

The faulty diode is the one between the yellow transformer and the 2 blue caps