42" LG30-UA backlight/inverter issues

[Austin420]

First post after following badcaps for awhile, so let's get right to the heart of the issue!

Model: LG30-UA
Issue: Worked fine one night before going to bed. When I woke up in the morning it didn't.
Symptoms:When I turn it on it briefly displays the source name "HDMI 1" (since that was the last input it was on). The backlight lights up temporarily and then the TV shuts back off. The red led in the bottom right slowly flashes then turns blue after the screen shuts off.

I purchased a new power board from shopjimmy.com because after talking to their tech, and having fixed a couple TV's before it seemed like the most reasonable cause. Tried installing new one, same issue.

I searched this website and came across this thread
https://www.badcaps.net/forum/showthread.php?t=10439
I know it's a different model, but very similar design.

In that thread they discuss several issues that may result in the issue. I decided to check the CCFLs in the back of the TV thinking that this could result in a faulty start-up. The attached image shows that the last 1/3 of a bulb is very dark. I'm assuming that it is burn out, and this is the cause.

The nitty gritty of my post is this:
1) Is this most probably the cause
2) If so does this mean that either/both the master+slave inverters need tobe replaced as well?
3) If I replace the bulb and not the inverters will it blow again?

I don't have a multimeter and it is my fault I didn't check the readings before ripping apart the TV.

[cashkennedy]

Re: 42" LG30-UA backlight/inverter issues

The bulb could be having trouble because it is burnt/ burning out, or because the transformer that powers it has a short.

To be sure which is the problem youd have to have a multimeter to test the resistance of the secondarys of the transformers. If the one with the bad bulb is lower resistance then the rest, then its the transformer not the bulb.

(you test for resistance on the transformers with the tv unplugged, and it requires a multimeter, if you dont know which pins are the secondary then youll need to post a picture of the transformers on your inverter, as well as a picture of the back of the board where the transformers are)

[Austin420]

Re: 42" LG30-UA backlight/inverter issues

Thanks for your response. To clarify are you asking for a picture of the board that the actual CCFL connects to or the inverter board itself?
The inverter board has only 1 outgoing wire from the main and 1 from the slave board to all of the ccfls. I'll upload a picture of those in the next 5 mins or so to this post.

[Austin420]

Re: 42" LG30-UA backlight/inverter issues

Attached are the front's of the boards taken off from an ebay listing. I am waiting for my actual pictures to upload, but they are the same exact part #, and indentical.

[selldoor]

Re: 42" LG30-UA backlight/inverter issues

We need to see yours, fronts and backs and really clear.

[Austin420]

Re: 42" LG30-UA backlight/inverter issues

Attached are fronts and backs of inverters let me know if I need a close up of anything in particular.

[tom66]

Re: 42" LG30-UA backlight/inverter issues

With power disconnected check between pins 12 and 9 on each transformer on each board. They should both show the same value I think.

[tibimakai]

Re: 42" LG30-UA backlight/inverter issues

I would replace that ccfl with another one and see if it will lit up there or not.
If not then you need another on. check ccflwarehouse.com, just measure yours and get the same size dia. x length(only the glass).
Be careful with everything, especially with the screen itself before you place back the top metal cover. Make sure that it sits where it supposed too, don't ask me how do I know.

[Austin420]

Re: 42" LG30-UA backlight/inverter issues

I'm going under the assumption that I don't want to measure in mV since that is a really low measurement. If that is the case when I put my multimeter in 40V range I get zero's across the board for all 4 transformers (the big black squares on the boards) when connecting pins 9&12 on each board individually.

[tibimakai]

Re: 42" LG30-UA backlight/inverter issues

you need to be on OHM, not Volt.

[Austin420]

Re: 42" LG30-UA backlight/inverter issues

Results done leaving multimeter in "auto range mode"

Left on Slave: 1 bar + .6 ohm
Right on Slave: No reading

Left on Master: 1 bar + .6 ohm
Right on Master: No reading

Results are done with multimeter checking continuity

Left on Slave: Short
Right on Slave: Open

Left on Master: Short
Right on Master: Open

According to multimeter manual:
Open-Open appears if circuit resistance is great than about 80ohms
Shrt& buzzer sound- If circuit resistance is less than about 80 ohms


This is the multimeter I am using:
http://www.radioshack.com/product/in...ductId=2103176

[retiredcaps]

Re: 42" LG30-UA backlight/inverter issues

Results are done with multimeter checking continuity


According to multimeter manual:
Open-Open appears if circuit resistance is great than about 80ohms
Shrt& buzzer sound- If circuit resistance is less than about 80 ohms

Use ohms, not continuity. We are looking for the exact ohms reading of the secondaries.

[Austin420]

Re: 42" LG30-UA backlight/inverter issues

Results done in 400 ohm max reading range.

Left on Slave: 1 bar + .6 ohm
Right on Slave: No reading

Left on Master: 1 bar + .6 ohm
Right on Master: No reading

The bar is said to be "8 segments represents units for the selected function".
It connects two lines, so fills up 1 segment and reads as stated above. Is this not what you are asking for. Sorry I'm being so difficult. First time with a multimeter.

[tom66]

Re: 42" LG30-UA backlight/inverter issues

Can you use 4000 ohms?

[Austin420]

Re: 42" LG30-UA backlight/inverter issues

Yes, when I test at any other level the one's that registers as minimal ohms give an actual 0 reading while the others just result in none. As in the multimeter displays the same reading as when the prongs are not touching anything.

I know the multimeter works because I've tested the MOSFETS and they all return a 10 ohm output. Maybe the only thing I'm doing wrong is that I'm just testing the boards taken completely off the TV. As in how they are pictured is how I am testing them. No wire attached from power board or to the CCFLs.

Is it simply that all of these are just blown and I would be better off replacing the boards and buying a new CCFL just to make sure I cover both? I'd rather not do that as it costs much more $$ and it's damn near impossible to find these boards.

P.S. I really appreciate all the questions and the responsiveness of this forum!! Thanks so much.

[tibimakai]

Re: 42" LG30-UA backlight/inverter issues

the cheapest is to move that bulb in another slot and see if it lights up or not.

[Austin420]

Re: 42" LG30-UA backlight/inverter issues

Hmm that requires reassembling the entire electrical system. Which I am not opposed to, just involves putting everything back together.

And this system has only 2 wires from the inverters that power all of the bulb. It's not like some of the others that I have done where each bulb has it's own plug-in on the inverter. So I'm not sure if simply moving the bulb to another location will solve it?

The original issue is that the TV only turns on for a few seconds, including the backlights, then shuts itself back off. So if simply switching the spots of two bulbs will tell me that the one that looks blown is then I suppose I will do that tomorrow. Will check back here before I go on that endeavor.

[cadiman]

Re: 42" LG30-UA backlight/inverter issues

This panel will have at least 3 ccfls bad and the slave inverter will have one or more shorted mosfets.

All of the l/gs with -ua after the model number use this au-optronics panel.(junk)

example: 32lg30-ua or 42lg30-ua ( Made for and sold by big box store? )

The better l/gs are the 32lg30 or 42lg30 etc. Those use the better panel with a single inverter.
The mainboard and t-con are different also and not interchangeable.

The power supplies are the same.

I have replaced the ccfls on these panels by using ccfls from other panels with no problem.

I also solder them in since the ends may be different.

A bad connection / ccfls will cause the inverter voltage to sore way over 1200 volts. (no load) and most likely take out the mosfets on the slave inverter board.

You can unplug and remove the slave inverter and the tv will still turn and have the 2 seconds to black.

[Austin420]

Re: 42" LG30-UA backlight/inverter issues

This panel will have at least 3 ccfls bad and the slave inverter will have one or more shorted mosfets.

You can unplug and remove the slave inverter and the tv will still turn and have the 2 seconds to black.

I attached a picture of the ccfls with the slave inverter unplugged. It seems as though only 1 is not working. As you can see at the bottom, the last 1/5th or so of each of the bulbs are not lighting up. I'm assuming that this is because of the slave inverter being disconnected.

[Austin420]

Re: 42" LG30-UA backlight/inverter issues

Attached is the same slave inverter with the MOSFETs numbered and the corresponding writing & numbering on each:

1)NIKOS P2504EDG WN37J0605

4.1 ohms

2)NIKOS P1504BDG WN37J0Q01

4.0 ohms

3)NIKOS P1504BDG WN37J0Q01

9.96 Kohms

4)NIKOS P2504EDG WN37J0605

20.20 Kohms

When I test all of the P250... on the Master they all test at 10.4ish Kohms
When I test all of the P150... on the Master they all test at 10.8ish Kohms

Is number 4 doubling because number 1 is essentially dead? And I'm assuming 2 is probably dead too?

If this indeed the case could anyone tell me what I need to replace them from? Preferably from the radioshack website since there is one less than 1/2 mile from where I live?
I apologize for all the questions in one post.

Thanks.