Wbox 55UD-H8076-0490(K550wdc2) - Backlight Driver

[eyeTech]

Hi all, looking for some help diagnosing the powersupply / LED driver on some tvs. I have 5 of them all with the same issue that are out of warranty and would like to fix for my customers.

Then powering on the TV the backlight will blink on then turn off untill the next power cycle. The LED driver output will go to proper voltage(200Vdc) for less than 1sec then drop to under than 10v. Will do the same thing is leds are disconnected.

BL_ON has 1.5ish volts

LED Strips all turn on with a tester. one of the tvs does have a dead strip.

Seems like it uses a Switch mode power supply but cant find schematics and
am hitting the edge of my knowledge.

Any help would be appreciated.

https://drive.google.com/drive/folde...kU?usp=sharing

[dick_barton]

Re: Wbox 55UD-H8076-0490(K550wdc2) - Backlight Driver

What voltages do you have for BL Adj, BL On/Off, 12V, 5V, 5VSB, PWR ON Off
If you have the voltages then if you connect 5VSB to PWR ON OFF using a 1K resistor and also 5VSB to BL On/Off using a second 1K resistor do the backlights come on.

Is the IC burnt ?

[eyeTech]

Re: Wbox 55UD-H8076-0490(K550wdc2) - Backlight Driver

BL adj - 2.7
BL ON - 1.4
12v - 12.2
5v - 5
5vsb - 5
PWR on off- 3.6

When jumpered to pwr the board powers on. then jumper to BL On/Off they do not even blink. when powering on with the power button they blink on.

That is just part of the transformer and glue on it.

[dick_barton]

Re: Wbox 55UD-H8076-0490(K550wdc2) - Backlight Driver

The two solder pads in the red box do not look good.

[eyeTech]

Re: Wbox 55UD-H8076-0490(K550wdc2) - Backlight Driver

Isnt actually anything soldered to those pads. I looked at all the solder joints under a microscope so i dont "think" its a bad joint. Wish it was tho!

On one of the boards i shorted the opto coupler when i was probing and the leds do turn on. There is high voltage on the high side of the transformer but seems like the feedback circuit is shutting it down.

[budm]

Re: Wbox 55UD-H8076-0490(K550wdc2) - Backlight Driver

What are the Voltage reading for each LED - (Cathode) pin of each LED string when you first turn on the board? You will have to keep the probes in place and do the test 3 times, one for each LED string.

[eyeTech]

Re: Wbox 55UD-H8076-0490(K550wdc2) - Backlight Driver

The leds blink on for too short of time for the meter to register any voltage. there are only 2 strings of leds as well

[bohaboha]

Re: Wbox 55UD-H8076-0490(K550wdc2) - Backlight Driver

Hi eyeTech have you solved the problem with your 5 Wbox 55UD-H8076-0490(K550wdc2) ? it would help many others if you could share your experience

[neilc6]

Re: Wbox 55UD-H8076-0490(K550wdc2) - Backlight Driver

Backlight issues are 99% the backlights themselves. Flash of backlights is a symptom of shutting down into protection mode. Led tester may not pick up since it is a lot lower current than normal settings. Replace all the strips with new and turn down the backlight level since they all have wear.

[bohaboha]

Re: Wbox 55UD-H8076-0490(K550wdc2) - Backlight Driver

Thanks so much neilc6 for the information .in my case it's a Voxicon that I found on the street when I started it worked then after 10 minutes it went out tried to restart but nothing comes except a blue light on the panel but when you press off it flashes the logo and then
goes off and it has the same designation K550WDC2 i will open a new thread for it