I refuse to give up ... (LG OLED65C7)

[ThomasX]

... sooner or later someone will respond to one of my posts

My LG OLED65C7 turned black and quiet. When turned on, it stayed on for 20 seconds and then shut down.

I measured the power board voltages and signals, and the DRV_ON was 1.6 volts, but 24VT was 24V.

Then i removed both the MB and the PB to inspect them.

Put them back, and connected a USB mouse.

Then the TV turns on, and does not shut off after 20 seconds, it stays on.
And the DRV_ON is now 3.0V!

I am confident there is no issue with the PB, all voltages seems ok.

But the TV is still black and quiet.

The DPC signal is 0V, and I have not been able to find out what it's for.

The TV shows up on the wifi router, so it does connect. When I connect a USB hard drive, the TV apparently reads from it.

So, it seems the MB is now working as it should, but I don't get any picture.

Any suggestions on how to progress?

Thanks!

[ThomasX]

Re: I refuse to give up ... (LG OLED65C7)

Whoooopss!!!!!

It turned out I had disconnected the TCON ribbon cables in both ends, and not re-connected them at the TCON side when I put the MB back.

When I connect the TCON ribbon cables from the MB, I am back to the situation where the TV shuts off after 20 seconds. So that to me is a clear indication the problem is at the TCON or later.

So now the question is, how do I remove the heat sink plate from the TCON in a good way, without damaging the IC that it is stuck onto?

Thanks!

[Maalobs]

Re: I refuse to give up ... (LG OLED65C7)

Post some pictures of the PCBs.

See if the service manual that's downloadable from this page, covers your model:
https://www.electronica-pt.com/esque...ileinfo/67106/
The manual seems quite comprehensive, with a nice troubleshooting chapter.

As for the heatsink, if it's the kind that is a stamped plate of aluminium and you have removed any screws from it, it's probably stuck with a double-sided adhesive tape on the main IC where there is a stamped pit in the plate.
You can heat it up with a hot air station to help loosen it, but it's enough to simply start rotating the plate back and forth clockwise-counterclockwise on an axis around the pit where the adhesive is.
Small movements, be very patient, and as you go on you notice that it's allowing you bigger and bigger movement until it pops off.

[dick_barton]

Re: I refuse to give up ... (LG OLED65C7)

Is Vx1 as shown in the manual at 0V ?

[ThomasX]

Re: I refuse to give up ... (LG OLED65C7)

Hi

Thanks for your responses! Much appreciated!

That service manual does not match my model nr precisely. But I have another one that does. However, strangely enough, the manual you link shows the VX1 in the correct position on my MB, while the manual I had before with the correct model nr, does not. Strange.

The VX1 voltage is as follows

Voltage across Resistor = 0 V
Voltage on both sides of the resistor vs GND = 1.37 V
It's unambiguous which voltages is ment.

Thanks for the tip about the heat sink plate. It came off nicely and easily from the TCON, it's the MB that will be the tricky one. It got 4 connectors through the PCB, so wont allow twisting.

I think the best lead I have now is the DRV_ON signal that shows the following behaviour

DRV_ON = 1.6 volts when TCON-MB Ribbons connected, TV turns off after 20 seconds
DRV_ON = 3.0 volts when TCON-MB Ribbons disconnected, TV stays on

So I am assuming that the DRV_ON has a pullup on the MB, but is also connected with the TCON that for some reason pulls it down to 1.6 volts. I will search for the DRV_ON signal on the Ribbon connectors, and see if I can trace it into the TCON board.

EDIT: Nope, no direct connection of DRV_ON to TCON.

What does it mean that VX1 is locked? I understood that is a good thing.

[ThomasX]

Re: I refuse to give up ... (LG OLED65C7)

Change the power board, they said
Change the mother board, they said
Change the TCON board, they said

I would've been ruined

I used what I had and changed C956 and F3.
Cost zero €, it was all in my "goodie bag"

And now the TV works again! YIHAAAAAA

It was a capacitor on the TCON board that had shorted, which in turn led to Fuse F3 blew.

Thanks for your support!

Took what I had, car fuses works in TV's too

[dick_barton]

Re: I refuse to give up ... (LG OLED65C7)

It would be useful if you would identify the capacitor in the event that someone at a later date may have the same problem.

[ThomasX]

Re: I refuse to give up ... (LG OLED65C7)

Capacitor was C956, but it's more or less just a coincidence it was that particular one. It could've been any one of 20 or so caps in the power area of the TCON board.

[petehall347]

Re: I refuse to give up ... (LG OLED65C7)

10 amp fuse ?

[ThomasX]

Re: I refuse to give up ... (LG OLED65C7)

That's what it said on the board just text to the F3 fuse, 125V/10A

The 24VD voltage is 24V 15A from the power board, considering the size of the TV and the light power with an all white screen, I'm not at all suprised

I'm more suprised the capacitor didn't blow before the fuse did, though

[dick_barton]

Re: I refuse to give up ... (LG OLED65C7)

I would suggest you change the fuse for the original type fitted which will have quite different properties to the automotive fuse.

[ThomasX]

Re: I refuse to give up ... (LG OLED65C7)

Yup, it's already on order

Will replace all those caps as well with new ones while I'm at it

I couldn't find any capacitors of the same package and value with a rating higher than 25V, which could explain the why it broke, as it's on the 24VD circuit.

I bet there's lot's of LG OLED TV's out there that got the TCON, and possibly more, boards replaced, just because a 5 cent capacitor shorted out.

Will replace mine for a higher voltage rating.

[Davi.p]

Re: I refuse to give up ... (LG OLED65C7)

Capacitors must be low esr, not good idea for me to replace the working ones..