Panasonic TX-L42U2E faulty backlight/inverter (arcing/spark sound)

[Dannyx]

Good day everyone. Got this Panasonic TX-L42U2E LCD TV which has some backlight issues. The thing I noticed right away, even before taking the back cover off, is that when the TV tries to switch on, the backlight fires up for a split second accompanied by a pretty noticeable spark-like sound before the set shuts down with a blinking red light on the front. The sound is identical to a xenon camera flash firing, like a *pop* - my mate took a video of it, though the quality isn't the best. Taking the cover off didn't reveal any visible signs of arcing damage or damage insulation on the HV leads leading into the panel. It's one of those dual inverter sort-of deals, which I hate for some reason...you've got 2 boards with 2 transformers and 4 FETs each. Pictured is the "master board" where the arcing sound seems to be coming from. I initially thought the insulation on the HV lead on that side might be pierced or have a "pore" though which the HV seeps into the metal chassis around it, so I even went through the trouble of taking apart the panel (much like you'd do for an LED replacement) and examined the leads and lamp terminals, but unfortunately there was no sign of any damage there either, so at this point I'm pretty sure it's the inverter to blame (sorry for the slightly askew picture - it was taken from underneath the table ). To be fair, I haven't actually checked the fuse on that inverter, so perhaps there's a short on it and it's only the other board that causes that brief pulse which is enough to trigger the lamps but not sustain them. What do you guys think ? Is this a lamp or an inverter fault ?

[dick_barton]

Re: Panasonic TX-L42U2E faulty backlight/inverter (arcing/spark sound)

The solder joints on Q1 & Q3 do not look very good.

[Dannyx]

Re: Panasonic TX-L42U2E faulty backlight/inverter (arcing/spark sound)

The solder joints on Q1 & Q3 do not look very good.

I'll probably reflow the board anyway, but I do agree they look a bit tatty...

[vinceroger69]

Re: Panasonic TX-L42U2E faulty backlight/inverter (arcing/spark sound)

maybe the invertor transformer breaking down under load?

[budm]

Re: Panasonic TX-L42U2E faulty backlight/inverter (arcing/spark sound)

Do you also smell OZONE?
Look at the what going in a dark room.

[Dannyx]

Re: Panasonic TX-L42U2E faulty backlight/inverter (arcing/spark sound)

Do you also smell OZONE?
Look at the what going in a dark room.

What does ozone smell like anyway ? I haven't played around with HV enough to find out *cough* Photonicindution *cough* It looks strange on video, but to the naked eye the backlight appears to be firing normally, albeit very briefly.

[dick_barton]

Re: Panasonic TX-L42U2E faulty backlight/inverter (arcing/spark sound)

If you have ever been next to a photocopier spewing out tons of paper, that's the smell of ozone.

[Dannyx]

Re: Panasonic TX-L42U2E faulty backlight/inverter (arcing/spark sound)

Update on this project: today I did a reflow on the inverter which seemed faulty and in the process I actually removed the transformer from the board entirely with intent of checking its underside for signs of arcing or burns. I couldn't see anything of the sort, however after putting everything back together and trying it out again, the issue was still there. Probing the thing with a meter while it was off the board didn't reveal anything suspicious either, which is telling me the transformer is probably arcing internally when HV forms. This time however I was also able to spot a little spark through the narrow gap between the two "blocks" of the transformer , which occurs right during that brief moment when the lamps fire. I assume it shouldn't normally do that, so I'm currently working on obtaining a pair of these inverters to see if that sorts it. I sure hope it's not a lamp issue, as that would make the purchase useless....

[dick_barton]

Re: Panasonic TX-L42U2E faulty backlight/inverter (arcing/spark sound)

Do you have a spare lamp from a broken down set that you could use to test the transformer.

[Dannyx]

Re: Panasonic TX-L42U2E faulty backlight/inverter (arcing/spark sound)

Do you have a spare lamp from a broken down set that you could use to test the transformer.

No I don't, but supposing I had one, how would I do that ?

[dick_barton]

Re: Panasonic TX-L42U2E faulty backlight/inverter (arcing/spark sound)

https://www.badcaps.net/forum/showth...ht=ccfl+tester

[vinceroger69]

Re: Panasonic TX-L42U2E faulty backlight/inverter (arcing/spark sound)

Update on this project: today I did a reflow on the inverter which seemed faulty and in the process I actually removed the transformer from the board entirely with intent of checking its underside for signs of arcing or burns. I couldn't see anything of the sort, however after putting everything back together and trying it out again, the issue was still there. Probing the thing with a meter while it was off the board didn't reveal anything suspicious either, which is telling me the transformer is probably arcing internally when HV forms. This time however I was also able to spot a little spark through the narrow gap between the two "blocks" of the transformer , which occurs right during that brief moment when the lamps fire. I assume it shouldn't normally do that, so I'm currently working on obtaining a pair of these inverters to see if that sorts it. I sure hope it's not a lamp issue, as that would make the purchase useless....

That certainly sounds like it could be the issue i would try a replacement transformer.

[Dannyx]

Re: Panasonic TX-L42U2E faulty backlight/inverter (arcing/spark sound)

https://www.badcaps.net/forum/showth...ht=ccfl+tester

Ok, I imagined something like that and have heard of it before, however I'm uncertain as to how well this would work with a large TV. My guess is that, even with a fully functional inverter setup, the inverter would detect an abnormal current draw and it would just shut off again...I may be wrong though and it might work. Also, not sure about what voltages are actually involved on the HV side and how drastically they differ from large TVs to small monitors.

[dick_barton]

Re: Panasonic TX-L42U2E faulty backlight/inverter (arcing/spark sound)

I bought a CCFL tube tester off Ebay which works really well. Doesn't test the transformer but does light up non faulty tubes.

http://www.dhgate.com/product/ccfl-t...159026302.html

[Dannyx]

Re: Panasonic TX-L42U2E faulty backlight/inverter (arcing/spark sound)

I bought a CCFL tube tester off Ebay which works really well. Doesn't test the transformer but does light up non faulty tubes.

http://www.dhgate.com/product/ccfl-t...159026302.html

Found that one in my country as well and was thinking of getting it (slightly more expensive that I would've liked it to be - thought of making my own for that reason), though I think that as long as the lamp is not cracked or otherwise physically damaged, it would light up anyway, making it hard to tell whether it's the or the inverter that's faulty...just a thought :|

[dick_barton]

Re: Panasonic TX-L42U2E faulty backlight/inverter (arcing/spark sound)

I only repair as a hobby so time is not an issue for me.
However, if you are doing it as a business then excessive time spent on a repair can be money lost so anything that can help you speed up fault-finding (as long as it's not too expensive) has to be useful.

[Dannyx]

Re: Panasonic TX-L42U2E faulty backlight/inverter (arcing/spark sound)

I only repair as a hobby so time is not an issue for me.
However, if you are doing it as a business then excessive time spent on a repair can be money lost so anything that can help you speed up fault-finding (as long as it's not too expensive) has to be useful.

Yes, I work in a service center which also does TV repairs whenever they come in. I've had a fairly high degree of success so far, despite not being a pro myself and sometimes resorting to help from others Will definitely get one of those.

[Dannyx]

Re: Panasonic TX-L42U2E faulty backlight/inverter (arcing/spark sound)

Replacing the inverter board fixed the problem, so the transformer was indeed arcing. Case closed - another few bucks in the "kitty"

[dick_barton]

Re: Panasonic TX-L42U2E faulty backlight/inverter (arcing/spark sound)

Glad you found the fix.