LG1934S Heat Problem?

[blokeman]

I've read the posts about 2 seconds and then black, often referring to LG1934's. Mine will stay on for anywhere from 5 to 20 minutes, will suddenly start to flicker slightly, dim and then go black. If I turn off the monitor power for a few minutes, then turn it back on, I have a screen for another 5-20 minutes. It feels like caps that are heating up, breaking down and then quitting. Any suggestions on where to start looking for bad caps? Power supply card? The monitor is about 5 years old, and I've ordered a replacement, but would like to repair this one for another computer, when the replacement arrives.

[smason]

Re: LG1934S Heat Problem?

Hi, welcome to BadCaps.

Look for swollen caps on the power/inverter board.
Also listen carefully for arcing noises that may point to a bad CCFL connection or a bad
solder joint.
Feel free to post pics and ask for further help, there are a lot of seasoned monitor repairers here.

[Lumberjack777]

Re: LG1934S Heat Problem?

Just by listening to your symptoms it sounds like a ccfl is going bad. Or bad wiring, or something in the inverter section.

If I turn off the monitor power for a few minutes, then turn it back on, I have a screen for another 5-20 minutes. It feels like caps that are heating up, breaking down and then quitting. Any suggestions on where to start looking for bad caps?

Believe it or not, an electrolytic aluminum capacitor actually has lower esr (better) as it gets hotter. So I wouldn't suspect caps.

You can try a diagnosis technique I learned from budm out here. Take a hair dryer and heat up different sections of the power board to see if it shuts off faster. But I wouldn't really superheat anything. Just a litle warmer and see if it shuts off faster.

I'm suspecting you have a bad ccfl; in which case the hair dryer won't speed up anything. The only way I can think to test that is to plug in a spare known good ccfl into each connector until you find one that stays on past 25 to 30 minutes. That would be your bad ccfl.
Unless anybody has any better suggestions

[blokeman]

Re: LG1934S Heat Problem?

Thanks for the replies. I just received notification that the new monitor will arrive tomorrow, so I'll work on this one this weekend and post what I find. Unfortunately, if it turns out to be a bad ccfl, it'll probably end up in the recycle bin, as I don't have a good one to test it against. Since it's been running for 5 years, I doubt anything has gone wrong with the wiring but a I suppose a cold solder joint could be showing up now. Anyway, I'll post what I find.

[budm]

Re: LG1934S Heat Problem?

This is an example of what happen to the caps when heated up, this monitor backlights start working after the caps are heated up, the ESR goes down.
https://www.badcaps.net/forum/showth...ghlight=AL2416

This is what happens due to poor wiring at the lamp's ends, common problem.
http://s807.photobucket.com/user/bud...?sort=3&page=1

[blokeman]

Re: LG1934S Heat Problem?

Well, I had it all apart, and there were no obvious signs of heated or expanded caps, All the components look as they should. I put it under power for a few minutes and there wasn't any arcing, or sound of any kind. A close inspection of the solder joints showed quite a few that were gray and suspicious. Overall soldering quality is typical of Chinese hand soldering. I re-soldered a large number of joints that looked suspicious and put it back together. When I turned it on, it ran for 2 1/2 hours, making me think I blundered onto it, but then it failed again-- same symptoms. I didn't use the hair dryer approach because the space I had to work in didn't strike me as safe enough to work in with the panel attached. That might have turned it up, as I've had some success with heat guns in the past on computer boards. So, I'm giving it up. I have a refurbed 22" Samsung as a replacement and it's working fine. Thanks for the suggestions, the pdf service manual was a help in the disassembly/assembly.