LG 55EG910V - no power and no standby light

[AleMonti]

Hi everyone,
I'm trying to troubleshoot and repair this old LG OLED curved TV, model 55EG910V.
I did some basic troubleshooting and reviewed most related posts here, but I wasn't able to isolate the issue.

The TV shut itself off during playback and never came back to life - the standby light remains off. My dad claims that it has happened a few times in the past but the issue resolved itself after some time. Not this one.

After checking the basics I did the following:

• I measured all voltages and as expected the only active supply is the 3.5V standby. It reaches into the main board and IR/button assembly just fine, but the standby LED stays off. Pressing/holding the button or using the remote to turn it on does nothing.
• I tested the power supply by disconnecting it from the main board and the TCON. By shorting P_ON and DRV_ON to 3.5V I can hear the relay click and all outputs turn on. Even when loaded the supply is stable.
• I then tried to disconnect the main board, force the power supply on, and see if the panel would show some kind of test pattern or image. Nothing. Probing around on the board I could see the 24V rail being active, but no voltage on most components or test points. As far as I can tell, nothing got noticeably hot. I tried the same with the panel's ribbon cables disconnected and the results were the same.
• With the main board connected again and the ribbon cables of the panel left disconnected, I tried again, but to no avail.
• On the main board, I also tried to hold down SW201 while trying to power it on but nothing happened.

I still need to try to force the board to reset with the Headphone IR trick as I don't currently have the IR LEDs needed.

Now I'm stuck wondering what to check next and if a main board/TCON replacement is worth trying. Any advice is much appreciated.
Pictures are attached below.

Thank you

[Davi.p]

Try an half reflow to the bga chips on the tcon then turn on tv when slightly hot..

[AleMonti]

It's doable with a heat gun? I don't have a reflow plate. I think tomorrow I'll check the ceramic caps for shorts first. If there's a faulty component what could be a safe voltage and current to inject to try locate the shorted component? I'm thinking something that will be enough to melt wax or something.

[Davi.p]

Heat gun ok. Dangerous to inject voltage there. Don't do it..

[AleMonti]

Cool thank you.
Also, to test the TCON while it's disconnected from the main board, is connecting CN7 enough? That only feeds 24V. I wasn't sure if I could force the PSU on with the main board connected, so TCON was disconnected from P1 during my tests yesterday. Looking at it more now, that ribbon cable might carry 12V to the board. Do I have to jumper 12V to it? In that case I guess that would be on the top right corner where F1 is.

Another thought, if the issue is the TCON, shouldn't the TV turn on with it disconnected? I've already tested that and it doesn't. Maybe the main board is at fault here..
Anyway, I'll post an update tomorrow as I get to work on it

[Davi.p]

To test an lcd or oled tcon at bench, usually give it a 12v is enough, but in some models and some designs there could be a jumper to place to simulate the connected panel

[lotas]

Basically, in this chassis the motherboard is blocked due to the panel, to start the motherboard you need an LG service remote.
To start the power supply, you need to not only supply 3.5v to P_ON and DRV_ON, but also to 12v_ON, and it is better to do this through three 1kOm resistors.

[Davi.p]

Do you meant testing the panel stand alone? You have to enable the 3 sections like lotas post, but i suggest you to enable 24v delayed, after you probe for example avdd on the tcon..

[AleMonti]

As far as I could tell 12VT_ON only enables 12VT on P202, which is not connected to anything on my particular model. The other 12V rail, 12VM on P201, goes to the main board (and probably the TCON too through the ribbon cable, I have to check), and turns on with P_ON.

I'll try testing the panel alone again as you suggest. Probably the reason why I wasn't getting any voltage on the TCON was because of the missing 12V. Now, to do this test, should I force the PSU on with everything connected or is it better to bypass the main board and deliver 12V to the TCON via a jumper on F1?

About the LG service remote, by browsing around on the forum the other day I found wav files to play through a makeshift IR blaster.. I'll try those too and report back.
I've attached them here as I can't find the post where I've got them from anymore.

[Davi.p]

or is it better to bypass the main board and deliver 12V to the TCON via a jumper on F1

Yes you have to..

1K resistors are not needed if you have trouble find them.. a jumper is enough.. so P-ON + 24V-ON, and stop....

[AleMonti]

Ok I've connected the TCON to 12V via F1 and now I can see that most parts of the circuit have voltage, yet no image. I've turned on 24VD too. The board draws around 0.25A on the 12V rail, and UC19 gets warm to the touch. I tested all the ceramic caps on the TCON and there were no shorts I think.

With the ribbon cables going to the panel disconnected, some test points measure different voltages:

	panel connected	panel disconnected
VGL	0.18	-7.05
VGH	0.26	23.0
VGL_SOUT	0.34	2.61
VGH_SOUT	2.02	3.83
EVSS_6.5V	6.56	6.57
PG_1.5V	4.68	4.67
VDD	0.45	16.1

Are those normal?

I also tried the IR file with everything connected normally but nothing. Maybe I'm doing it wrong? With my phone's camera I can see the IR led illuminating with one of the files.

Any other thing to try or test? I think reflowing should be the last resort as it's quite easy to mess it up with the heat gun.

[lotas]

Well, you see, when you connect the panel, the voltage on the T-con is blocked due to a non-working panel...

[AleMonti]

I see, makes sense. Should I just scrap it then? A replacement it's not worth it

[Davi.p]

NO WAIT.... check the panel pins connected to VDD respect to GND, maybe there's a shorted cap there...

[crazycavan]

on this chassis the main problem is IC3000

[AleMonti]

Testing the TCON with the left most ribbon disconnected from the panel I get a white line! I think that confirms the panel being the issue? I've tested all the exposed caps and they seem fine to me. I guess there are more under the metal chassis... maybe it's time to get the Dremel..

IC3000 on the mainboard controls the wake from standby as far as I know. It probably also gets feedback from the TCON, so refuses to turn on the TV after detecting the issue

[Davi.p]

if VDD it is not shorted at panel, i don't think panel must be damaged, if you feel the cost is acceptable and trust me, try.at least a tcon on market, 2 only requisites: 1) brand new or 2) extracted from working set (cracked panel)

[lotas]

if VDD it is not shorted at panel, i don't think panel must be damaged, if you feel the cost is acceptable and trust me, try.at least a tcon on market, 2 only requisites: 1) brand new or 2) extracted from working set (cracked panel)

These models LG 55EC930V, LG 55EG910V..., the panels are dying like flies, and no new T-CON will help here...

[Diah]

OP you are doing wrong OLED Panel will never work with disconnecting ribbon cable one or more between T_CON and panel... just because of the EVDD VCC >22V will go around over all 4 ribbon.long...

you need to disconnect the LVDS from MB to T-con and the socket between PSU and MB and switch power on on psu to turn on 12V and evdd 24V. include power by using the stand by 3.3V via 1KR

[AleMonti]

Diah I don't see your point, I think I'm doing the test correctly. TCON connected to PSU via CN7 and to 12VM (on the PSU) through a jumper on F1. The mainboard was completely disconnected. I then forced the PSU to turn on with the standby 3.5V bridged to P_ON and DRV_ON. Because the panel might have been shorted and overloading the buck converters on the TCON, I tried disconnecting it from its ribbon cables and the voltages didn't drop anymore. My take away is that the panel is shorted, either internally or on its small bottom edge boards. But I could be wrong.

Davi.p, I'll go back tomorrow to double check if VDD is completely shorted on the panel or not as I don't remember testing that. I could try getting a replacement TCON, they are just 14€ on AliExpress. But wouldn't a new one show artefacts because of the mismatched panel calibration?