LG55UH615T pulsating Redstanby LED

[wushumike]

LG model 55UH615T when plug into AC, the Red standby light pulsating slowly. Not sure if it is logic board or power supply.

Troubleshoot Power board as follows.
1. Connect to AC source
2. Measuring P201 connector, there are 7.8V from the 5 pins.... assuming this is the standby voltage.
3. Connect the 7.8V via a 1K resistor to PWR_ON pin, the output change to 13.2V ....so I would assume the power is correct.

4.There is no 186Vdc for the backlight.... Not sure if this should turn on with step 3.
5. Voltage across the two caps is 284Vdc..
6. Any expert in this power supply ?
7 What would be the likely problem,... or could it be the logic board ?!

[wushumike]

Re: LG55UH615T pulsating Redstanby LED

Update on further testing.

I have disconnect the backlight connection and try power on. Now the standby LED is normal..... it only blink when I connect back the backlight connector. I would assume that the motherboard is working because without the backlight connector, I can see faint image with torchlight shining on screen.... although no sound, but could be the tv setup... not sure because difficult to run setup without light....

Any expert to comment ?

[nomoresonys]

Re: LG55UH615T pulsating Redstanby LED

ok, same test, cable from powerboard to mainboard UNHOOKED, resistor from standby to power on and add 2 more resistors from standby to both pdim 1 and pdim2, retry see if that 186 voltage goes higher and if the backlights come on and stay on.

[wushumike]

Re: LG55UH615T pulsating Redstanby LED

ok, same test, cable from powerboard to mainboard UNHOOKED, resistor from standby to power on and add 2 more resistors from standby to both pdim 1 and pdim2, retry see if that 186 voltage goes higher and if the backlights come on and stay on.

As per instruction, without connecting motherboard and pull up PWR_ON, PDIM1, PDIM2 and with backlight connected, NOT lighted up....

I remove the backlight connector to measure voltage of LED+ with reference to chassis ground. Pin 7 (LED+) = 30VDC ; Pin 1 (LED+) = 300Vdc.

There are two pairs wires both LED+/LED- ....... the copper trace LED+ is common, but the LED- is not.

I do not have a LED backlight tested so no able to check the LED strips...

[nomoresonys]

Re: LG55UH615T pulsating Redstanby LED

seems like a backlight issue, what was the voltage across those caps with those jumpers in place? careful HIGH voltage there.

[Storyteller12]

Re: LG55UH615T pulsating Redstanby LED

These TVs have a lot of bad backlight issues. Sad part is only 1 led has to go bad for the whole tv to shut down.
Replacing backlights and turning the backlight setting down usually solves the issue. You can also modify the board to lower the amps to the backlights.
There is a thread that describes the process

[wushumike]

Re: LG55UH615T pulsating Redstanby LED

seems like a backlight issue, what was the voltage across those caps with those jumpers in place? careful HIGH voltage there.

As I have did a preliminary check on the power board backlight related component, all seems to be OK... and also when I remove the backlight connector, the stand-by light is back to normal.... it can turn on and also can see faint image with torchlight test.

Anyway I have decided not to waste money and time on this TV, I have decided to go thru the tedious way and remove the panel to physically check the backlight led. ( Just to satisfy my curiosity and doubt)

Voila.... the right side LED was burnt at the very end.... I will get a new pair of the LED strip and try installing back.... Hopefully I don't break the LCD panel along the way... Will update

[wushumike]

Re: LG55UH615T pulsating Redstanby LED

These TVs have a lot of bad backlight issues. Sad part is only 1 led has to go bad for the whole tv to shut down.
Replacing backlights and turning the backlight setting down usually solves the issue. You can also modify the board to lower the amps to the backlights.
There is a thread that describes the process

Kudos.... You are absolutely right. As I do not wish to spend too much time and money on this TV, I remove the LCD panel to check if it is really the LED problem.

Upon dismantling, the right side LED strip was burnt at the very end... I have remove and physically check both strip to see what is the extend of the damage. The left strip all LEDs are OK. For the right side, apart from the burnt end, in between there are a few shorted LEDs.

I would assume the power board sense that the voltage or current drawn is not correct and trigger a fault signal.

P.S. As there are two sets of LEDs, left and right. I did try powering individual strip by removing one set from the connector. It didnt work although I assume half of the screen would light up.

[Diah]

Re: LG55UH615T pulsating Redstanby LED

yours Photo ... its look to me not LED defect... but connection defect to the next or to return line on same strip.. easy can be repaired .

[wushumike]

Re: LG55UH615T pulsating Redstanby LED

After replacing both LED backlight. The power board seems to be damage too because the backlight still not lighted up.

Searched and bought an old power board from China seller...fixed to the TV, one side light up normal but another side the LED is dim. Attached photo.

P.S. Initially I thought was the new backlight LED giving problem, I swap the pair of LED of left to right side and now the right side brighten up and normal.

Anyone can advice if it is this replacement board is also faulty?... The measured voltage again chassis ground is Pin 7= 269V ; Pin5= 117V ; Pin 3=269V ; Pin1=106V

Is there any repair recommendation rather then getting another unknown condition board from CN.

Power Board: EAX66944001(1.4)
LG P/N EAY64388821
TV Model : 55UH615T-TB

[Davi.p]

Re: LG55UH615T pulsating Redstanby LED

3. Connect the 7.8V via a 1K resistor to PWR_ON pin, the output change to 13.2V ....so I would assume the power is correct.

Power on pin must not exceed 5v, with one resistor you can't decrease voltage, two resistors needed..voltage divider, 13v> 3v, 13v--W---3v---W---0v, 13v -- 3,3kohm -- 3v -- 1kohm -- 0v

..and also.. never connect a 7v/13v to any other pins, like pdim! Must decrease voltage before..
who has suggested you has probably broke your precious board!

[wushumike]

Re: LG55UH615T pulsating Redstanby LED

I bought a second hand power board from CN.... all working except the right backlight LED is very dimly lited

When replace, the right side backlight LED is dimmer....and the Left side is OK...

Initially I thought the new LED strips are giving problem... so I swap the pair of LED ie left connection to right connection.... Now the one that was dim lights up without problem..... So to say the backlight LED is not the problem

I'm not sure if this second hand power board is faulty or not.... but then again, the backlight LED strips both are tested OK

[Davi.p]

Re: LG55UH615T pulsating Redstanby LED

ah ok now is clear , yes it seems no good power board..

[wushumike]

Re: LG55UH615T pulsating Redstanby LED

ah ok now is clear , yes it seems no good power board..

Many time getting old boards from CN reseller is a gamble because they dont usually test the boards if is OK .....This is the second time I encountering.....Previous repair I bought a samsung ps....so badly repaired and not working and they refuse to refund...bought again from another supplier and it works.

[wushumike]

Re: LG55UH615T pulsating Redstanby LED

ah ok now is clear , yes it seems no good power board..

Any sugguestion for repair? ... The right and left sets of LED are common LED+ but the return path goes separate ways for this power board.

[Davi.p]

Re: LG55UH615T pulsating Redstanby LED

probably the backlight manager ic is no good , post a clear picture of the back of board, if the return wire goes directly to ic then ic is bad, instead if it goes to a separate mosfet it can be bad too

[wushumike]

Re: LG55UH615T pulsating Redstanby LED

probably the backlight manager ic is no good , post a clear picture of the back of board, if the return wire goes directly to ic then ic is bad, instead if it goes to a separate mosfet it can be bad too

Picture showing the backlight section...is the set LED +/- on the right side that is problematic

[nomoresonys]

Re: LG55UH615T pulsating Redstanby LED

try something simple, like cleaning and reseating the ribbon cables.

[Davi.p]

Re: LG55UH615T pulsating Redstanby LED

in your last photo, check those 2 to252 mosfets, if them are ok repkace ic801

[lotas]

Re: LG55UH615T pulsating Redstanby LED

Throw the wires on the cable, and you will find out where the problem is in the power supply or in the LED bar.