37" LG 37LC7d No picture, No Backlight.

[shtnarg]

Hello.

A friend of mine found a 37" LG, which he brought to me to see if I could repair it. Simple, or so I thought....It was clearly opened before, likely with a crowbar as there are a few broken plastic screw tabs. But it doesn't look like anyone attempted a repair.

A few Caps on the power supply were clearly bulging, I replaced everything I had replacements for 10x 10v 2200uf. I replaced with 16V 2200uf. They are cheap ebay ones.. I will replace with low esr versions if and when these fail.

The blinking green light now went solid, but still no picture. So I started tracing some voltages. 12v = 13.8. 6v= 5.4. 3.4=3.4 19v=19.5
I assume the 12v being so high is an issue, as well as the 6v being 1V low. I browsed the forums and found a similar issue but a different model (32lc2d). I can't locate voltage regulators. All the caps on the questionable rails were replaced(I think).

NOW I realized I have another similar tv that I replaced caps on the PSU and it fixed it right up. an LG 42LC7D. So I opened it up, and the boards seem similar minus one HUGE cap on the PSU. I played some adult lego I tried the main board from faulty 37" in known working 42" and everything works.
Then I tried the working 42" mainboard in the 37" and no difference.
I tried the known good 42" PSU with its respective mainboard with the questionable 37" screen and t-con board (I think) and still no picture. I haven't tried switching the t-con boards because I'm not sure thats safe?

Sound works, I can blindly switch inputs, just NO backlight and NO picture with 2 different PSU boards and Main boards.

Help! What can I provide? pics/more details?

[newtothis]

Re: 37" LG 37LC7d No picture, No Backlight.

Pictures and get your DMM ready

[shtnarg]

Re: 37" LG 37LC7d No picture, No Backlight.

Here are pics of the 37" LC7D.
Fluke 87 III by my side.

[shtnarg]

Re: 37" LG 37LC7d No picture, No Backlight.

From the PSU

P203 (all grounds read -.006)
12v=12.43
6.5=6.28
3.4=3.462

p201
ACD =4.89
ON/OFF=2.882
ST5V=5.00
INV-CNTRL=3.087
ERR=.229
BURST-DIM=.033
ST5V=5.00
A-DIM=.025
6.5V=6.28
3.4V=2.377 :/

P202
12v=12.42
3.4v=3.449
6.5=6.28
19v=19.50

[budm]

Re: 37" LG 37LC7d No picture, No Backlight.

"I tried the known good 42" PSU with its respective mainboard with the questionable 37" screen and t-con board (I think) and still no picture. I haven't tried switching the t-con boards because I'm not sure thats safe? " With this setup, do you get the backlights but no pictures? BTW, "its respective mainboard" Do you mean the 42" main board?

[shtnarg]

Re: 37" LG 37LC7d No picture, No Backlight.

Yes exactly, 42" mainboard AND the 42" powersupply (both display a picture on the 42")
Show absolutely nothing while connected to the 37".

[budm]

Re: 37" LG 37LC7d No picture, No Backlight.

So no backlights, that will leave you with bad lamp then if that is the case regardless if you can see the image on the panel or not, it should at least light up the backlights.

[shtnarg]

Re: 37" LG 37LC7d No picture, No Backlight.

I've tried desperately to see a picture and NOTHING.

So there are only 2 more components correct? The screen and the T-con board? how can I t-shoot the t-con board?

How Likely is it that the screen(and backlight I suppose) are just dead?

[budm]

Re: 37" LG 37LC7d No picture, No Backlight.

I would try getting the backlights to come on first with your good boards. T-CON can be replaced or may be repaired, but bad lamps will get real expensive.

[shtnarg]

Re: 37" LG 37LC7d No picture, No Backlight.

What can I try with the good boards (the "questionable" boards produce a picture when installed in the 42") to get backlights?

Its seeming like the screen/backlights have been damaged and both are not worth repairing.

[budm]

Re: 37" LG 37LC7d No picture, No Backlight.

Is there cracks on the screen? Can you hear any rattling sound in side the LCD panel? It may have broken lamps.
You already try using good power supply/inveter and main board from the 42" and it does not light up the screen (and the "questionable" boards produce a picture when installed in the 42")), so there is not much left to check but the lamps in the panel.

[shtnarg]

Re: 37" LG 37LC7d No picture, No Backlight.

No cracks I can see. I will take a very close look.

On the right side, there is a clip, with a pink wire that goes to the high voltage side of the PSU. Said clip is very loose and rattles back and forth. Im going out on a limb amd assuming that's a connector for the backlight?

[budm]

Re: 37" LG 37LC7d No picture, No Backlight.

Yes.

[shtnarg]

Re: 37" LG 37LC7d No picture, No Backlight.

Alright. On that note I don't believe there's any point in trying any further.

Is it worth trying to sell the boards?

Anyone interested?

[shtnarg]

Re: 37" LG 37LC7d No picture, No Backlight.

Thanks Budm as well as other responders for your help. If anyone is in need of parts for a LG 37 lc7d, send me a PM.

[gaztolmie]

Re: 37" LG 37LC7d No picture, No Backlight.

Hi,

Just looking at the forum, trying to find the answers to a backlight problem with the bosses tv.

I'll be checking the threads for a while to see if it's been answered already. ( last TV I worked on professionally was CRT with paper capacitors. )

Garry - Victoria - Australia.

[gaztolmie]

Re: 37" LG 37LC7d No picture, No Backlight.

Couldn't find an answer ( or didn't look hard enough )

If the backlights turn on for a few seconds then turns off obviously something not all running as planned. - all lights are ok, so what signal turns the them off?

Have replaced the board with the faulty capacitors ( the original fault - boss happy to replace board than to repair it ) - LG sent the later board "42" rather than the "37".

We have access to LG parts but as not service agent no access to their doco"s.

Am I missing something obvious?
Gaz