Troubleshooting LG TV 60UH8500. TV is not powering on

[KKinNJ]

Hi,

I'm new to this forum, so this is my first post. I have an LED TV LG Model 60UH8500 that stopped working suddenly. The standby LED is on, but when I try to turn the TV on either using the remote or the power button on the TV, the red standby LED blinks 3 times, but nothing else happens - the TV screen stays dark, no picture and no sound.

Here is what I did so far... I removed the back cover and checked both the power supply board and the main board for any obvious visual cues such as burnt diodes, bulging caps, etc. Nothing observed. I checked 2 fuses - GOOD, tested all capacitors and diodes that I could - found nothing. I also tested the voltages at the following spots:

In Standby mode:
12V: 7.8V
24V: 0V
POWER_ON: 0V
DRV_ON: 0V
LED+: 43V

After turning on:
12V: 11.9V
24V: 24.8V
POWER_ON: 3.1V
DRV_ON: 0V
LED+: 63.7V

With the back cover removed I could observe that after 10 seconds or so after powering the TV on the amber LED on the power supply board LD701 blinks 5 times then off for about 5 seconds and then blinks 5 times and it repeats indefinitely. I think it's some kind of error code, but I couldn't find anything that would explain or narrow things down for me.

I'm trying to narrow things down to either a power board, a main board or something else, to see if I could fix this or not. Any help with what I should test next would be appreciated.

[KKinNJ]

Here are the pictures of the power supply board in case this helps...

[nomoresonys]

Probably faulty mainboard, DRV_ON signal comes from mainboard, it's the backlight on signal.

[nomoresonys]

I think for good measure, maybe touch up any suspect solder joints on powerboard: https://www.youtube.com/watch?v=5F4sX2Pn-Iw

[KKinNJ]

Probably faulty mainboard, DRV_ON signal comes from mainboard, it's the backlight on signal.

That was my thinking too, but how can I be sure? Can I somehow exclude the possibility that this is the power supply? I tried bridging the POWER_ON to DRV_ON to see if the backlight comes on, but it didn't. I just don't want to buy a new main board without knowing it will fix the issue. Also, If it is the main board, is there a way to troubleshoot why it's not sending the DRV_ON signal?

[EazyBone]

Have you tested the LEDs? That would be my obvious first thing to do?

Have you turned on the TV and held a flashlight up to the screen and looked around to see if there is picture??

Also how did you bridge pwr on and drv on? Main board connected or just standalone psu

[KKinNJ]

Have you tested the LEDs? That would be my obvious first thing to do?

That's what I tried to test when I bridged POWER_ON with DRV_ON. My thought that if there is voltage on DRV_ON then the backlight should come on.

Have you turned on the TV and held a flashlight up to the screen and looked around to see if there is picture??

I tried that and it wasn't totally black as when it's off, it looked like there was something, but it wasn't a picture that would make sense - it was like just random colors in different pixels.

Also how did you bridge pwr on and drv on? Main board connected or just standalone psu

I bridged it with the main board connected. Just shorted the two contacts with a wire briefly.

[EazyBone]

No you have to test the LEDs without that circuit with a tester or something. That narrows it down. Then we know we need to look at it or not. Then we know it's PSU or MB.

Try taking the DRV pin out of the harness from the MB but leave all the rest of the pins in place, then jump it so it's not potentially shorting on the MB (not sure if this is good advice but I do it and it works)

Also, those lines on the screen.... Uhh, that's important lol what is going on there? How do you get that

[KKinNJ]

Try taking the DRV pin out of the harness from the MB but leave all the rest of the pins in place

I'm not sure I follow.... How do I take a single pin out from the connector without damaging it?

Also, those lines on the screen.... Uhh, that's important lol what is going on there? How do you get that

I'm not sure what lines are you talking about...

[EazyBone]

Sorry *random colors on screen. Explain what's going on.

And take the connector out, you lift the tiny tab with some tweezers or something and it pops up, then you pull the wire out.

[KKinNJ]

Thank you EazyBone and nomoresonys for your help with this. I got a new main board and the TV is fixed, so it was the main board after all. I suppose the random colors was also a symptom of that, but I can't be sure now, as I don't know what's supposed to be on the screen in such a failure mode.

[nomoresonys]

Yep, typical mainboard failure, glad you took the advice, thanks for followup.

[EazyBone]

awesome