LB5550 Backlight blinks

[XpressComputers]

Re: LB5550 Backlight blinks

looks like BLU202B

[budm]

Re: LB5550 Backlight blinks

BL0202B (BL0200 series)
https://cdn.badcaps-static.com/pdfs/...bf5e314100.pdf

[XpressComputers]

Re: LB5550 Backlight blinks

ok so i checked all the pins in reference to ground and there are no shorts on this IC. what should i be looking for next?

[budm]

Re: LB5550 Backlight blinks

There is problem with the LED string that is connected to pin 3 and pin 4 of the LED connector, that Voltage reading on pin 3 Cathode return is way too high. You need to verify the Voltage reading again on pin 3 of the LED connector.
The IC Voltage boosters are working otherwise you will not have those High Voltage on the LED + pins.

[XpressComputers]

Re: LB5550 Backlight blinks

ok i'll double check my readings again. i see the output voltages for LOW and HIGH labeled on my PSU at 145V and 218V. How can i tell what the cathode return is supposed to be?

[budm]

Re: LB5550 Backlight blinks

It should be around 20 ~30V range

[XpressComputers]

Re: LB5550 Backlight blinks

i double checked the readings at the LED pins and they are as i posted before

[budm]

Re: LB5550 Backlight blinks

1) TV OFF.
2) Remove the LED connector.
3) Set meter to over 200V scale
4) Keep black meter probe on chassis.
5) Put red meter probe on pin 4 of the LED connector on the power supply board.
6) Turn on the TV and see how high the Voltage jumps up too and wait 10 seconds to see how low it goes down too.
7) Repeat step 5 ~ 6 but move the probe to pin 3. Do the same again on pin 2, pin 1.

[XpressComputers]

Re: LB5550 Backlight blinks

with the LED connector unplugged, pin 1 and 3 are 0V pin 2 fluctuates between 160 and 170 pin 4 fluctuates between 205 and 215

[XpressComputers]

Re: LB5550 Backlight blinks

finally got a chance to open the TV all the way to see the LED strips and found many LEDs burnt out. Changing them out now.

[budm]

Re: LB5550 Backlight blinks

Another fail LED problem, so typical and sad.

[XpressComputers]

Re: LB5550 Backlight blinks

yup, thanks for all the input though. learned a lot here.

[sintv]

Re: LB5550 Backlight blinks

All these posts where obviously some LEDs are faulty. You should have stripped out the screen and powered the set up on its back where you would have seen faulty non lighting LEDs.

[budm]

Re: LB5550 Backlight blinks

Taking apart the LCD panel is the last thing you will want to do only after other tests have been done first.