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Old 06-11-2018, 09:08 AM   #1
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Default LB5550 Backlight blinks

I have an LG LED tv here that has standby voltage, and upon pressing the power button the LEDs blink on and off every few seconds. Even when the LEDs are off the display can still vaguely be seen. The voltage at the LED connector fluctuates
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Old 06-11-2018, 09:11 AM   #2
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Default Re: LB5550 Backlight blinks

We need to see the pictures of the whole back side of the TV showing all the boards.
We also need to see the Voltage readings of all the pin at the connector of the power supply board that goes to the main board, also the Voltage readings of all the pins of the LED connector.
You MUST put down the pin name and follow by the Voltage reading for each pin, giving just the Voltage reading without the pin name will be useless.
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Old 06-11-2018, 10:52 AM   #3
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Default Re: LB5550 Backlight blinks

LED connector has voltage fluctuating as stated before,
itsjust 4 pin LED + - + -

main board connector is as follows
GND - 0V GND - 0V
12V - 12V NC - 0V
12V - 12V 12V - 12V
GND - 0V GND - 0V
24V - 24V 24V - 24V
GND - 0V P-DIM2 - 1.2V
3.5V - 3.5V 3.5V - 3.5V
3.5V - 3.5V P-Dim1 - 1.2V
PWR-ON - 3.3V DRV-ON - 3.3V
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Old 06-11-2018, 10:53 AM   #4
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Default Re: LB5550 Backlight blinks

i also tried it with the main board unplugged and the LEDs still blinked.
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Old 06-11-2018, 11:48 AM   #5
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Default Re: LB5550 Backlight blinks

Quote:
Originally Posted by XpressComputers View Post
LED connector has voltage fluctuating as stated before,
itsjust 4 pin LED + - + -
Quote:
Originally Posted by XpressComputers View Post

main board connector is as follows
GND - 0V GND - 0V
12V - 12V NC - 0V
12V - 12V 12V - 12V
GND - 0V GND - 0V
24V - 24V 24V - 24V
GND - 0V P-DIM2 - 1.2V
3.5V - 3.5V 3.5V - 3.5V
3.5V - 3.5V P-Dim1 - 1.2V
PWR-ON - 3.3V DRV-ON - 3.3V
Yeah, but fluctuation between what value to what value on each pin? We need the numbers!
What is the power supply board P/N?

Last edited by budm; 06-11-2018 at 12:54 PM..
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Old 06-11-2018, 12:26 PM   #6
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Default Re: LB5550 Backlight blinks

pin 1: 25-30
pin 2: 102-125
pin 3: 102-155
pin 4: 230-260

as best as i could get them
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Old 06-11-2018, 01:03 PM   #7
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Default Re: LB5550 Backlight blinks

TV full model number is 55LB5500?
What is the LCD panel model number?

Shop jimmy version 1.0 Power supply board: LG EAY63072101 Power Supply / LED Board, http://www.shopjimmy.com/lg-eay63072...-led-board.htm.

Can we see straight shot pictures of the whole top and the bottom side of your? I cannot use the pictures from shopjimmy because PCB version is 1.0, your board is 2.1.

Last edited by budm; 06-11-2018 at 01:58 PM..
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Old 06-11-2018, 01:52 PM   #8
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Default Re: LB5550 Backlight blinks

yes thats the full model
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Old 06-11-2018, 01:57 PM   #9
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Default Re: LB5550 Backlight blinks

LCD panel model number?
I need to verify the LED strips being used, so far all I know that it has two LED strings with two driver circuits with two different Voltages outputs (145V and 218V as printed on the board Version 1 and also on your board).
So based on your readings, they do not look right and point o bad LEDs.

Last edited by budm; 06-11-2018 at 02:01 PM..
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Old 06-11-2018, 02:30 PM   #10
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Default Re: LB5550 Backlight blinks

i appreciate you posting your thought process, its actually very helpful for me. I will get the panel number as soon as i can. might be tomorrow though.
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Old 06-11-2018, 02:58 PM   #11
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Default Re: LB5550 Backlight blinks

here's what i got
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Old 06-11-2018, 03:55 PM   #12
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Default Re: LB5550 Backlight blinks

Model LC550DUE (FG) (A6).
I will look up the spec. sheet to get the LED info.
I still need the high res picture of the bottom side of the board to verify the LED driver circuits and how the LEDs are connected.
BTW, do you LED tester? Something similar to this: http://www.shopjimmy.com/sid-gj2c-le...ght-tester.htm
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Old 06-12-2018, 06:46 AM   #13
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Default Re: LB5550 Backlight blinks

i do have the LED tester from ShopJimmy, i will test them now and also get a pic of the board.
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Old 06-12-2018, 07:20 AM   #14
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Default Re: LB5550 Backlight blinks

here's the bottom of the PSU

can you talk me through what exactly you're looking for?
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Old 06-12-2018, 09:19 AM   #15
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Default Re: LB5550 Backlight blinks

I am checking to make sure that there are two LED strings driven by two LED driver circuits, which they are.
So what does the LED tester meter show for each string of the LED?
The LED string connected to pin 3 and 4 look to be where the problem is.

Last edited by budm; 06-12-2018 at 09:22 AM..
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Old 06-12-2018, 09:31 AM   #16
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Default Re: LB5550 Backlight blinks

tester showed 200v at pin 3,4 and 100v at pin 1,2
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Old 06-12-2018, 09:33 AM   #17
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Default Re: LB5550 Backlight blinks

can you point out to me where you see the two LED strings and drivers?
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Old 06-12-2018, 09:41 AM   #18
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Default Re: LB5550 Backlight blinks

You have TWO LED + and TWO LED -, as you look at the bottom side, then you can easily see how each LED string is connected to the driver circuits.
See the two surface mounted MOSFETs close to the LED connector? Each LED - is connected to the Drain of the MOSFET, the Source is connected to the current sensing resistor and then to GND.
There are two Voltage boost converter circuits for each LED string that feed each LED +.
Get the P/N of that SMD IC close to the MOSFET to get the spec. sheet then you will see how it works.
The LED string that show 200V withe tester which only putting out around 20 ~ 30mA, at 400mA the Vf of the LED string will be much higher than 200V, LED power supply for that string is rated at 218V.

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Old 06-12-2018, 10:09 AM   #19
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Default Re: LB5550 Backlight blinks

these are what you're talking about, correct? i'm gonna pull up data sheets for these and try to learn something
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Old 06-12-2018, 10:11 AM   #20
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Default Re: LB5550 Backlight blinks

https://www.badcaps.net/forum/attach...1&d=1528819719
I cannot read the p/n on the top line.
BD???????
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