LG 55LB6100 Backlights flashing 4 second interval

[jcamerox]

I tried disconnecting one LED strip and the backlights didn't come on at all. Disconnecting the other led strip and the backlights flashed at the 4 second rate. The capacitor voltage seems unsteady, with no backlights its about 210 v
and with the flashing backlights reading about 250 v.

[Andrew F. Ali]

Re: LG 55LB6100 Backlights flashing 4 second interval

From what I gather from the info you gave.....You seem to have a backlight issue....LEDs are open on the strips.....there could be shorting LEDs, too.

[jcamerox]

Re: LG 55LB6100 Backlights flashing 4 second interval

Thanks for the reply Andrew. I thought that if i disconnected one strip and the other was good, I would get half the screen illuminated, but this is not the case. With one strip disconnected I get no backlights at all, with the other disconnected I get the flashing backlights. Any ideas on where to go from here?

[budm]

Re: LG 55LB6100 Backlights flashing 4 second interval

So you have two LED driver circuits, and two LED strips.
what DCV do you have for each set of the LED at the L+, L- of each set of the outputs with LED connector in place and without LED connector in place?
https://www.badcaps.net/forum/attach...8&d=1493218780

[jcamerox]

Re: LG 55LB6100 Backlights flashing 4 second interval

Thanks for the reply, BudM, I was hoping for you, I have seen some great posts from you.

With the led strip connector plugged in and power on, between led- and led+ for strip 1, a varying voltage from 1.5 v to 22 v seems like open circuit, almost random. On strip 2 between + and - about 155v and 135v. It seems to charge up to 155v, the backlights flash very quickly and then it discharges to the 135 v or so and then charges up again.

With led strips disconnected, Led strip 1 is varying from 50 to 60 v while strip 2 is varying from 90 to 110 v.

Incidentally, with power connected and set not turned on there is about 90 v on the capacitors near the LED connector but the led + and - outputs are near 0

thanks again, jim

[budm]

Re: LG 55LB6100 Backlights flashing 4 second interval

I forget to tell you to use chassis GND as the GND ref for the meter and test all 4 pins of the connector with ref to Gnd. Please take the reading again.

[jcamerox]

Re: LG 55LB6100 Backlights flashing 4 second interval

Voltages with respect to chassis ground,

Power plugged in, power switch off, led strips connected
Led strip 1, led - 1.4 v led + 90.0 v
Led strip 2, led - 150 mv led + 90.2 v

Power plugged in, power switch on, led strips connected
Led strip 1, led - 1 to 12 v led + 111 to 115 v
Led strip 2, led - 1 to 60 v led + 245 to 260 v

Power plugged in, power switch on, led strips disconnected
Led strip 1, led - 360 mv led +163 to 173 v
Led strip 2, led - 380 mv led + 225 to 195 v slow drop as if it's discharging through

voltmeter and then charging back to 225 v

[budm]

Re: LG 55LB6100 Backlights flashing 4 second interval

So if you only have LED strip 2 connected, do you see the backlights flash on for seconds?
All 3 sets of the readings do not have have logical relationship at all.

[jcamerox]

Re: LG 55LB6100 Backlights flashing 4 second interval

With power on and led strip 1 connected and led strip 2 disconnected, the backlights flash in a sequence bright, dim, faint in about half a second then back to bright with bright to bright about 4 seconds.
the voltages at the connector are;

Led strip 1 led - 14 to 19 v led + 109 to 115 v
Led strip 2 led - 10 to 15 mv led + 200 to 260 v

But strip 2 is disconnected so where is the flash coming from??? Strip 1 doesn't have enough voltage to flash or it is too fast to see with my voltmeter ?

With power on and led strip 1 disconnected, and strip 2 connected there are no backlights or backlight flash

Led strip 1 led - 25 to 35 mv led + 165 to 175 v
Led strip 2 led - 45 to 55 v led + 200 to 220 v

[budm]

Re: LG 55LB6100 Backlights flashing 4 second interval

You have two individual LED driver circuits. The LED connector has Black (Cathode, L-) and Blue (Anode, L+) wires for one set of LED strip, Black (Cathode, L-) and White (Anode, L+) wires for another set of strip.
So which set of wires that are hook up and give the backlights for seconds?

[jcamerox]

Re: LG 55LB6100 Backlights flashing 4 second interval

I'm calling the white and black pair strip 2. So when the black and blue pair are connected I get the backlights flashing. This strip would seem to be the top half of the led screen.

Just went back and checked the voltages with strip 2 disconnected, the voltages are

Led strip 1 led - 15 to 25 v led + 110 to 115 v
Led strip 2 led - 10 to 15 mv led + 245 to 265 v

[budm]

Re: LG 55LB6100 Backlights flashing 4 second interval

OK, so "So when the black and blue pair are connected I get the backlights flashing." It means that strip does not have open circuit, but it does not mean it does not have shorted out LED/S.
So how about the WHITE/BLACK pair only, do you get the lights for seconds or not?

[jcamerox]

Re: LG 55LB6100 Backlights flashing 4 second interval

When white/black pair connected only, nothing at all. No flashing.

[budm]

Re: LG 55LB6100 Backlights flashing 4 second interval

When white/black pair connected only, nothing at all. No flashing.

Well, there you go. You can also further verify by swapping the two set of the LED connection, just like swapping lamp socket to see if the problem will follow or stays the same.

[jcamerox]

Re: LG 55LB6100 Backlights flashing 4 second interval

Good idea. I swapped the leads in the connector and the symptoms are exactly the same.
Therefore, not the power supply, one of the strips could be open circuit and the other could have a shorted led.

That's all for tonight, 11:30 pm here, thanks for the suggestions BudM

jim

[jcamerox]

Re: LG 55LB6100 Backlights flashing 4 second interval

One thing did change, the flash rate went from 4 seconds to about 2 seconds.

[RinusB]

Re: LG 55LB6100 Backlights flashing 4 second interval

My issue is not the LEDs, it is the power going there.
With power plugged in and TV on, the Blue/Black back light voltage goes from over 200 to zero exactly the way the LEDs flash. When I disconnect the back light LEDs the same power fluctuation occurs at those pins at the connector
Might this indicate a main board issue?
No trace of issues to be seen on both side of the boards.
This issue started when I set my energy saver setting to any settings but off!
Now it is like that full time even when the back lights are set to the lowest setting.
Yes there is a normal picture as well as menu.
Hope you can shed light on this.

[budm]

Re: LG 55LB6100 Backlights flashing 4 second interval

It goes over 200V because you have open circuit is one of the two LED strings.
See post 9, 10, 11 and read the whole thread.

[RinusB]

Re: LG 55LB6100 Backlights flashing 4 second interval

Hi budm
Yes read the whole thing and it might indeed be the LED string.
The voltage on the black led- lead that should read 0v actually reads between 10 and 50 volts. That same lead on the white/black pair reads zero.
Does it indicate an open circuit or a short or does it matter?

Thanks.

[budm]

Re: LG 55LB6100 Backlights flashing 4 second interval

You have two power supplies to drive each LED string, when the LED power supply does not see the load (I.E. open circuit in the LED string) the Voltage will go up high (that is why you see the Voltage goes up over 200V) and then the Over Voltage protection will kick in. The reason you see the backlights come on for seconds because one of the LED drive circuit ans the LED string are working, and one is not (the one that the output went up over 200V).
Bad LED is common failure in TV with LED backlights, the worst one are the LG, it drive the LED at or beyond the limit of the LED.
This one could have burn down the house.
https://www.badcaps.net/forum/showth...ht=LG+47LN5790
https://www.badcaps.net/forum/showth...hlight=latw%2A