LG 42LN5200-UM Has backlight, audio. No picture

[marimol]

Hello everyone,

I have acquired an LG 42LN5200-UM TV from a family member. I want to see if I can get some help finding out what's wrong and seeing if a repair is worth it. I was told that a couple of days ago when they turned the TV on, the only thing they got was sound. I opened it up and took some pictures with my phone, I don't have a real camera so I hope those will work OK.

I don't see any blown/bulged capacitors or any obvious signs of burnt components. The TV turns on, the backlight and sound are working and it appears to respond to inputs from the remote control. I tested the fuse in the t-con board and I get 0.1 Ohms, also tested it for continuity and it is OK. The only thing that I see is in the second picture, you can see some of the solder lines on the top left are missing; is that it?

Any input is appreciated. My level of electronics is not that advanced. I only did two semesters of circuits in school, it was 7 years ago too. I am more on the software side of things but if you need me to do/test something, I'll do my best.

Thank You in advance.

[Hamie]

Re: LG 42LN5200-UM Has backlight, audio. No picture

On the TCON you have various test points.

Post results for

Vcc
Vdd
Vgl
Vgh

[marimol]

Re: LG 42LN5200-UM Has backlight, audio. No picture

Thank you for the reply and sorry for the delay. I hope I am doing this right: Negative probe on ground screw, positive on test point while TV turned on.

Vcc: 2.05v
Vdd: 0v
Vgl: 0.009v
Vgh: 0v
Vcc18: 0.97v

Thank You.

[dick_barton]

Re: LG 42LN5200-UM Has backlight, audio. No picture

They don't look to good. What voltage have you on both sides on the white ceramic fuse F1.

[marimol]

Re: LG 42LN5200-UM Has backlight, audio. No picture

TV on, negative probe to ground, positive probe in turn to each side of fuse.

I have 7.99v on each side of F1

[dick_barton]

Re: LG 42LN5200-UM Has backlight, audio. No picture

Is this a set with an external 24V 3.5A power pack?

Edit
Looking at your first photo's it does look like.
Have you confirmed that you still have 24V DC when powering the TV and that the voltage has not dropped due to a problem either on the main circuit board or with the power pack itself. The power pack needs to be connected to the set and on to test.

[budm]

Re: LG 42LN5200-UM Has backlight, audio. No picture

Just to be sure, meter is set to DCV and the batteries are good?

[marimol]

Re: LG 42LN5200-UM Has backlight, audio. No picture

Yes, it has an external power brick: 24v 3.42A. I tested just the brick under no load and it gives 24.3v. I'll try to find the repair manual or some schematics of the main board so that I can see where I can probe for voltage while under load.

Thanks a lot.

Edit: @budm Yes, meter is set to DCV and I'll swap the battery for a new one just to be sure and I'll retest. Thank You

Edit2: Swapped the batteries on my tester and I get the same results.

[budm]

Re: LG 42LN5200-UM Has backlight, audio. No picture

Which are the boards that matched your boards?
Since you are able to read the 24V power supply correctly then your meter is probably OK.
I believe you have at least 4 Buck converter circuits on that main board, and the Voltage for the T-con should be around 12VDC.
I also see some 3-pin Vreg ICs.

[dick_barton]

Re: LG 42LN5200-UM Has backlight, audio. No picture

Ignore - reply to wrong post

[Richlee1970]

Re: LG 42LN5200-UM Has backlight, audio. No picture

Which are the boards that matched your boards?
Since you are able to read the 24V power supply correctly then your meter is probably OK.
I believe you have at least 4 Buck converter circuits on that main board, and the Voltage for the T-con should be around 12VDC.
I also see some 3-pin Vreg ICs.

I have the LG42LN5200-UM AND I am having same issue you had with yours
Blue screen did have snow sound now I've lost it and stupid joystick can't get sound back
What was the fix for your LG?
Rich