LG 65UH5500 Momentary Flash Of BackLights

[budm]

Re: LG 65UH5500 Momentary Flash Of BackLights

BTW, does this TV has WiFi since it is smart TV?
If it does, what happen if you disconnect it?

[nomoresonys]

Re: LG 65UH5500 Momentary Flash Of BackLights

The 7.5vDC for the 13V STBY may be normal in standby mode, since there is no separated standby power supply so they may keep the Voltage low just enough to run the main board, and when PS-ON is present and then the PFC Booster circuit kicks in then the 13V and the 80 will be normal.
That is why I ask OP to see what DC V he has on the main filter cap since the PS-ON is present.

This would explain a lot of half voltage readings we have been seeing here on lots of posts.

[budm]

Re: LG 65UH5500 Momentary Flash Of BackLights

Since you indicate that the Backlights did flash on for seconds, then you should unplug the TV and put black probe on the chassis, keep red probe on the 80V pin then plug the TV in and watch to meter to see if it jumps up to 80V or not, repeat the same test on the DRV_ON pin.

[nomoresonys]

Re: LG 65UH5500 Momentary Flash Of BackLights

Could try force on power supply to see if the 13 comes up, need to unplug from mainboard before test.

[Michale32086]

Re: LG 65UH5500 Momentary Flash Of BackLights

BTW, since you do have PS-ON, what DC Voltage do you have between the two legs of the main filter caps?

390v

Since you indicate that the Backlights did flash on for seconds, then you should unplug the TV and put black probe on the chassis, keep red probe on the 80V pin then plug the TV in and watch to meter to see if it jumps up to 80V or not, repeat the same test on the DRV_ON pin.

An 80v pin on the DRIVER board does jump to 80V and then drops to 55V...

The DRV ON pin "jumps" to 50mV, then goes haywire but never above 1V and then holds steady at .9V

BTW, does this TV has WiFi since it is smart TV?
If it does, what happen if you disconnect it?

No change after disconnecting the WiFi adapter..

[Michale32086]

Re: LG 65UH5500 Momentary Flash Of BackLights

Hmm, try unhook leds, then see if tv turns on and off with power button.

With the LED array unplugged, the TV still won't stay off..

Either by using the remote or holding the power button til shutdown...

The TV always comes back on...

[budm]

Re: LG 65UH5500 Momentary Flash Of BackLights

You have main board problem at this point, you should be able to turn off the TV if the power control function of the main board is good.
Usually if there is error signal such as bad T-CON, Backlights circuits, etc, the main board will be forced off, yours is stuck on.

[Michale32086]

Re: LG 65UH5500 Momentary Flash Of BackLights

Do you think it is the mainboard or the driver board. I am getting the same issue. Can you get any sound .

Haven't gotten any sound, but I am likely on an input other than TV so I wouldn't expect sound...

Let me see if I can switch it to TV and get a static sound..

[Michale32086]

Re: LG 65UH5500 Momentary Flash Of BackLights

You have main board problem at this point, you should be able to turn off the TV if the power control function of the main board is good.
Usually if there is error signal such as bad T-CON, Backlights circuits, etc, the main board will be forced off, yours is stuck on.

Yea, I'm beginning to think it's a Main board problem too..

I could have swore I checked and saw it had a latent image.. But I get one of the backlights on using my LED Power thingy and power up the TV and get no image at all...

That seems to seal the idea that it's a main board issue...

[Michale32086]

Re: LG 65UH5500 Momentary Flash Of BackLights

Found a replacement Main Board for a decent price...

Will follow up, once it arrives..

Thanx to all for the assistance and advice...

[nomoresonys]

Re: LG 65UH5500 Momentary Flash Of BackLights

With the LED array unplugged, the TV still won't stay off..

Either by using the remote or holding the power button til shutdown...

The TV always comes back on...

Ok, was mainboard test, mainboard failed.

[Michale32086]

Re: LG 65UH5500 Momentary Flash Of BackLights

Ok, was mainboard test, mainboard failed.

That's my guess as well.. I'll know in a few days

Thanx again..

[Michale32086]

Re: LG 65UH5500 Momentary Flash Of BackLights

And the plot, as they say, thickens...

I got the replacement Main board in...

Hooked it up and powered up the TV.... Same problem.. LEDs flashed for a second and then went off... :^(

Something weird happened though... In the brief moment where the LEDs were on, half the display panel was white and the other half, I *thought* I saw the regular LG start up graphic...

The white part of the panel indicated to me that the TCON board connector was not inserted properly..

Powered everything down and inserted the TCON connector properly..

Still have the momentary flash of the LEDs, but now there is nothing on the display panel.. Not even a latent display..

So, now things are exactly as before.... Nothing on the display panel, not even latent'ly... And only a momentary flash of the LEDs... And, I should note, the TV cannot be turned off...

As much as I hate to do it, I am thinking I am going to have to crack open the display panel and check the individual LED strips..

Bumper...

[budm]

Re: LG 65UH5500 Momentary Flash Of BackLights

OK, I am confused, in post #1 indicated the Display is fine just no backlights,so what happen if you put old main board back in?

[Michale32086]

Re: LG 65UH5500 Momentary Flash Of BackLights

OK, I am confused, in post #1 indicated the Display is fine just no backlights,so what happen if you put old main board back in?

Yea, I might have been mistaken about that initially...

Subsequently (a few days ago) I used my LED Power Supply to turn on a segment of the LED Array and then powered up the TV but I never got anything on the display...

So, either I just assumed that I got a display image based on my assumption it was an LED strip issue (possible)... Or I actually did have a latent image initially and my subsequent tinkering frak'ed that up (equally possible)...

I am leaning more towards I made a wrong assumption....

[Michale32086]

Re: LG 65UH5500 Momentary Flash Of BackLights

If I got a latent image, then a bad LED strip would make sense..

But not getting a latent image makes me lean towards a bad MAIN board.. Or, should I say ANOTHER bad MAIN board.. Which is possible, I spose...

Is there a way to jumper or short some connections on the Driver/Power board to force the LEDs on?? Leaving the MAIN board totally taken out of the loop???

[Michale32086]

Re: LG 65UH5500 Momentary Flash Of BackLights

Ohmigod!!! Ohmigod!!!

In an effort to confirm once and for all that the LEDs are not the problem, I hit on the idea of taking each pair of wires off of the DRIVER connector and place them on the DRIVER board one pair at a time..

Each pair gave me the same thing.. An LED strip/area came on then flashed off... So, that told me that the LED array is NOT the problem..

After I had tested the last pair, I put them back into the connector and then plugged the connector back into the DRIVER board...

Powered up the TV and, I'll be at some beach, the LEDs came on and stayed on!!!!

I thought to myself, I said, "Self!? Well, ya fixed the LED issue, but you still don't have an display.."

And, some beach again, I sure had a display!!!???

Apparently, it's all linked together.. You can't have a display if the LEDs aren't coming on and staying on...

So, not one to look a gift horse in the mouth, I am gonna count this one as a win!!

Thanks again to all who helped out...

[nomoresonys]

Re: LG 65UH5500 Momentary Flash Of BackLights

So it was just a loose connection on the led wires?

[Michale32086]

Re: LG 65UH5500 Momentary Flash Of BackLights

Apparently so... I physically pulled the wires from the DRIVER board connector and then replaced them after testing..

I can only assume that on wire wasn't seated properly and/or wasn't making a good enough contact with the plug...

Sometimes it's the simple things..

[Michale32086]

Re: LG 65UH5500 Momentary Flash Of BackLights

Do you think it is the mainboard or the driver board. I am getting the same issue. Can you get any sound .

I don't think your problem and my problem are the same..

One way to confirm that is to take a powerful flash light and shine it into the screen at an angle...

Turn the TV on.. If you see a latent image, then your problem is likely a bad LED strip... Those are a major bear to change, but is doable if yer careful..

If you don't see a latent image, then the problem is likely one of the boards. Most likely the Main Video Board..

If it IS a Main Board issue and if I can confirm that my old Main Board is good, I'll be happy to sell you the replacement board I got (which I know works fine) at the cost I paid for it...