LG 55LS4600 powers on with backlight no image

[woodman45]

LG 55Ls4600 as title says,powers on back lights are on no image.
Are there any tests I can do?
Is the main video board possibly bad?
Also to mention there is sound just no video.

[diif]

Re: LG 55LS4600 powers on with backlight no image

There's a fuse on the tcon to check, measure for 12v each side of it.

[woodman45]

Re: LG 55LS4600 powers on with backlight no image

Where is the fuse at on the tcon board

[nomoresonys]

Re: LG 55LS4600 powers on with backlight no image

Fuse is labeled F1 2A/125v, black negative probe on chassis/metal ground. red positive probe on each side of fuse.

[woodman45]

Re: LG 55LS4600 powers on with backlight no image

There's a fuse on the tcon to check, measure for 12v each side of it.

Yes 12v on each side.

[woodman45]

Re: LG 55LS4600 powers on with backlight no image

Fuse is labeled F1 2A/125v, black negative probe on chassis/metal ground. red positive probe on each side of fuse.

Thanks. Yes 12v on both sides.

[budm]

Re: LG 55LS4600 powers on with backlight no image

What do you get on the screen if you have only one cable between T-CON and LCD panel connected one at a time?

[yokoono]

Re: LG 55LS4600 powers on with backlight no image

Measure the voltages circled in red and post the values found.

[woodman45]

Re: LG 55LS4600 powers on with backlight no image

What do you get on the screen if you have only one cable between T-CON and LCD panel connected one at a time?

Left connector in pic did nothing,right connector unplugged showed half screen.

[woodman45]

Re: LG 55LS4600 powers on with backlight no image

Measure the voltages circled in red and post the values found.

The reading on vcc18 is 1.8
Vgl reading is -6.91
Vgh reading is 0.00
Vod reading is 0.19

[yokoono]

Re: LG 55LS4600 powers on with backlight no image

You have problems with the part where there is no image. Connect the defective part and measure the resistance at the VGH point. You can compare with the good side.
L.E.
It's a short on the VGH rail. You can leave the good side coupled and measure VGH. It can be a short or resistive smd cond, a diode or, worse, the panel.

[woodman45]

Re: LG 55LS4600 powers on with backlight no image

You have problems with the part where there is no image. Connect the defective part and measure the resistance at the VGH point. You can compare with the good side.
L.E.
It's a short on the VGH rail. You can leave the good side coupled and measure VGH. It can be a short or resistive smd cond, a diode or, worse, the panel.

Those readings are with both sides connected.
I found a tcon board for $20, I think I'm gonna get it and if I get the same results is it safe to say the panel has a short?

[budm]

Re: LG 55LS4600 powers on with backlight no image

It can be as simple as shorted out caps on the tab bonding board of the bad side.

[woodman45]

Re: LG 55LS4600 powers on with backlight no image

It can be as simple as shorted out caps on the tab bonding board of the bad side.

Should I get the tcon first?

[budm]

Re: LG 55LS4600 powers on with backlight no image

I would start checking the caps first, you do want to damage T-CON board if you have shorts circuit on the tab bonding board.

[woodman45]

Re: LG 55LS4600 powers on with backlight no image

I would start checking the caps first, you do want to damage T-CON board if you have shorts circuit on the tab bonding board.

Thanks budm. Which caps should I check on the tab bonding board?
I have searched on internet but I can't find much info.
Any insight is greatly appreciated.

[budm]

Re: LG 55LS4600 powers on with backlight no image

All the SMD caps on the tab bonding boards, you need to check for very low resistance reading.
You do know what the tab boding boards are, correct? You need to remove the LCD frame to get to the tab bonding board.

[woodman45]

Re: LG 55LS4600 powers on with backlight no image

All the SMD caps on the tab bonding boards, you need to check for very low resistance reading.
You do know what the tab boding boards are, correct? You need to remove the LCD frame to get to the tab bonding board.

I'm assuming the tab bonding board is the board on the bottom that connects into the panel.
With SMD caps how do you read the resistance?

[budm]

Re: LG 55LS4600 powers on with backlight no image

No power to TV, set meter to Ohm mode, 200 Ohm scale, then just check the resistance between the two legs of each cap.

[woodman45]

Re: LG 55LS4600 powers on with backlight no image

No power to TV, set meter to Ohm mode, 200 Ohm scale, then just check the resistance between the two legs of each cap.

Thanks again budm. I found a video of a guy with similar problem and it was a smd cap on the panel driver board.he shows how to get to it and do the tests.
I will get back and report my findings.