LG UH652T doesn't turn on and stands is blinking once a second

[mar1in]

Hi everyone,

I've got this LG TV here that wouldn't turn on and be stuck in a standby loop (blinking red once every other second).
Did test the following:

* LED's seem fine as they all light up using LED Tester
* Power Supply supplied around 111V for each LED Strips (2x edge lid strips)
* PWR_ON would be at around 3V but dropping every other second (just like the standby light)
* DRV_ON is doing the same
* power supply has a green LED onboard, but that doesn't seem to do anything (stays off the whole time).
* there is a tiny clicking sound (no relay) coming from the mainboard somewhere every time the PWR_ON signal would be on.
* tried unplugging backlight cables, LCD cables but the symptom would stay the same.

My experience is rather low on this but I would assume it's either a faulty power supply or mainboard.
Anyone has had similar symptoms and was able to fix it?

[EazyBone]

Do you get 12v at the TCON fuse?

Also does PSU supply a 12v line? There should be some sort of 12/16/2x volts from the PSU, picture with legend would help also. And picture of all boards

[mar1in]

thanks, will check the TCON fuse when I get a chance.
sorry, should have posted some pics.

there are 5x 13.2V lines, each of them I'm getting 11.8V, is that because it's not yet powered on fully?

[mar1in]

actually there is no tcon board

[EazyBone]

Probably yes your missing the voltage from powering on..

I know these UH series have an issue with main boards failing. Check for shorted caps around the CPU.

[mar1in]

I have had a Quick Look and couldn't find any shorted ones, I will try again but the next step might be reflow/resoldering the cpu, or what do you think?

[mar1in]

Actually, I found 3 resistors shorted in the marked area. R8117, R8118 and R8028.
Need to check for a service manual to see if I can get those parts, or do you think there will be more shorted components than just those resistors ?

[EazyBone]

So small components like that can show continuity and nothing is wrong with them. I'm not advanced enough to answer if these in particular should read that way.. but I'm sure someone else can answer that here.

As for what's next... I couldn't really answer that either as I don't have enough experience fixing main boards.. most i can do is reflow a cpu. I would plug it back in and look for voltages leaving the CPU if any are present and at different gates in the board. This might give a clue

[mar1in]

The reason why I think they are shorted is because the ones next to them that are same or similar size have 3-5k value of resistance.

but I've heard that resistors are not really failing, its most likely other components. I'm quite a beginner in troubleshooting but I have skills to replace parts of the board. I just recently bought a hot air station, might try an cpu reflow and see how that goes.

[mar1in]

I've managed to get the exact same model (in working condition) for cheap on marketplace and did the following to help troubleshooting:

1. take out working mainboard and put into non working TV => issue still present, TV doesn't turn on, standby LED wouldn't flash anymore but stay solid
2. take out working power supply and put into non working TV => TV turns on and works
3. take out working mainboard and replace with mainboard that was inside in the first place => TV turns on and works.

this means the problem is within the power supply board which was a surprise to me, as I had tested and all voltages were present. voltages fluctuates when mainboard was connected, but would stay stable when mainboard is unplugged.

would love to fix that power supply board, if I only knew what components are playing up.
anyone has any idea what I could try?