LG 42LV5500 only backlight on

[tom66]

Re: LG 42LV5500 only backlight on

You can see each of the differential pairs going into the T-con processor. They are the little traces that bunch together at the top of this board.
https://www.badcaps.net/forum/attach...8&d=1398637689

Pick a few, (doesn't matter which, try to get a random selection) and record what you get from them.

Set your scope to 500mV/div, 1us/div, trigger level 0V, bandwidth limit OFF, AC coupled.

Use the RUN/STOP button to pause the waveform, then take a photo or export it using the USB port.

[tibimakai]

Re: LG 42LV5500 only backlight on

Thanks Tom.
I will do this, when I'll be home.

[tom66]

Re: LG 42LV5500 only backlight on

Forgot to mention: use 10X probe, place ground clip on the LVDS connector body, and set scope to 10X mode.

[tibimakai]

Re: LG 42LV5500 only backlight on

Thanks.

[tibimakai]

Re: LG 42LV5500 only backlight on

Tom, what I will have to see, when I'm checking these point?
All of them should be pretty much the same? If something it's bad, there should be no signal?

[tom66]

Re: LG 42LV5500 only backlight on

It's hard to describe, a picture of the waveform will be enough, basically you should see a wave on each indicating the LVDS transmitter is working, and if you look carefully you should see some kind of modulated data for example if you have a "no signal" box on the screen you will see it disappear and reappear (for an LG TV.)

[tibimakai]

Re: LG 42LV5500 only backlight on

Do you think that I should play a movie on it, or just turn it on and do the measurements?

[tom66]

Re: LG 42LV5500 only backlight on

You can try with a movie because you might be able to see the scene brightness changes.

[tibimakai]

Re: LG 42LV5500 only backlight on

Finally I had some time to work on this TV.
To me it seems like there is video LVDS signal before the T_con IC.
How would I show you the wave form?
I have also noticed, that the main board's main processor, gets to hot after a while and shuts down.

[tibimakai]

Re: LG 42LV5500 only backlight on

gamma voltages GMA1 thru GMA18 far right

Tom, could you please point out the way, you would measure these points?
I'm having a hard time, figuring out the markings.

OK I have used WFMReader to save these files in jpeg format.
I have also noticed that at one of the pins(VGH_F) the voltage was once 29V then changed to -5V and then back to 29V and so one. I'm not sure what this means though.

[tibimakai]

Re: LG 42LV5500 only backlight on

Anybody?

[tibimakai]

Re: LG 42LV5500 only backlight on

These are, the right LVDS signals or not?

[tom66]

Re: LG 42LV5500 only backlight on

I have never seen the readings presented like that. However it looks right. One test you can do is to press the menu key, for example. The LVDS signals should visibly change. Do they?

[tibimakai]

Re: LG 42LV5500 only backlight on

I will measure when I'm home. I didn't thought about doing that, good idea.
It's hard to get to the right input without an image on the screen.
When I did this measurement, I had sound for a second and then went away. I assumed that the video it was still running.
Last time, when I worked on this TV, the sound it was very loud and I could not adjust the volume.
I did as you said, to set the scope. Then, I used Save to external storage and I have used that software, to take a snapshot from the wfm file and saved it as jpeg.
I believe, that software is a Rigol scope software.
Tom, could you please help me with that 65" Sharp?
I would like to test out the inverters, to see which one is not working properly.
Thank you for all your help, it's greatly appreciated.

[tibimakai]

Re: LG 42LV5500 only backlight on

OK, there is definitely change on the scope as I stop the movie, or select menu.
The main CPU on the main board is getting really hot. I have measured 51C deg. and I didn't want to keep it on to don't damage anything.
Last time, I have left it on for a bit longer, it started rebooting.
With or without ribbons connected to the panel there is no difference at all.
There is only backlight on. No video signal at all.
I don't like those missing voltages at the gamma test pints.
I could have got a bad T-con board?
Initially, both the old and "new" boards were showing the same exact voltages and the missing voltages were missing on both boards in the same spots.

[tibimakai]

Re: LG 42LV5500 only backlight on

I have got another T-con board. Same story, same voltages at the gamma test points.
What else can I check, the panel PCB?
TV does everything with the remote that it suppose to, so mainboard it's OK. There is sound, I can adjust volume, turn the TV on and off. I see LVDS signal with the scope.
What can cause this issue, at the panel/panel PCB?

[georgi]

Re: LG 42LV5500 only backlight on

12V both ends of T-con fuse?

where this 12 volts come from ?

[tibimakai]

Re: LG 42LV5500 only backlight on

Most likely power supply.

[ReeceyBurger123]

Re: LG 42LV5500 only backlight on

Also what did you do with the Tv in the end ?

[georgi]

Re: LG 42LV5500 only backlight on

12V both ends of T-con fuse?

Hi TOM
I have one of this same set , but there are no 12 volts in fuse of t-con board
fuse is ok , but there are no source for those 12 volts , any idea ?
thank you