A couple of LCD monitors

[Skymutt]

I work in a PC repair shop, so I'm intimately familiar with blown caps on boards. A couple months ago, someone brought in a gateway 19" LCD that wouldn't power up. Now, we don't really get into board level repairs here, but there had been some heavy storm activity that weekend, and I knew I could at least check the fuse for the lady so she knew whether or not to replace the unit. The fuse checked out, but there were several leaking and distended caps on the power module. Since we don't handle those repairs she bought a new one and told me to scrap the other. The same thing happened last week, this time with an HP 19" LCD. I've physically inspected both power circuits, and it would appear that the caps are the only problem. The transistors look fine, no cracks or the like.

Is it safe to think that the caps are the problem, or should I check for some other source before I waste time and money on recapping?

[PedroDaGr8]

Re: A couple of LCD monitors

From what I have read on here, on most backlight inverters the caps are the problem. The reason is lack of adequate ventiallation and the things just get to friggin hot. Unfortunately, it is not uncommon to have a tranny or two go out along with the caps.

[davmax]

Re: A couple of LCD monitors

While you are checking get yourself an ohmmeter and check for shorted transistors. Any shorted transistor will mean added complication such as a possible shorted turn in an inverter transformer. Some transistors just fail for unexplainable reasons, this happened to me recently and I see others have replaced transistors and all is well again!!! Check my post recently on Benq monitor if interested.

[starfury1]

Re: A couple of LCD monitors

seems psu's and inverters are the most trouble with lcd monitors...crap caps being one of them

possible storm damages is a different kettle of fish, check (varistors) MOV's are intact etc
but as Davmax pedro have said there are issues with transistors and inverter transformers that add to the mix.
so you need to at lest check for possible dead transistors.

mostly these days its replace the PCB thats the problem not component level repair
Here you will find most go to component level.

I suppose if you are possibly going to score something for the price of a few caps its worth the time.

I would do a net search with "fault faulty not working no power" etc and see what falls out too...it might just be a dog of a model not worth the time and effort.

me personally Id do the above and depending take a chance on the caps being the only issue.

It nice to save something from the scrap heap too

good luck

[Skymutt]

Re: A couple of LCD monitors

If the inverter(s) were the problem, wouldn't the display still power up? I know that in a notebook with a faulty inverter the display still operates, it's just too dim to notice for the most part. Since neither of my displays will even power on, that leads me to believe that the PSUs are faulty.

Also, I'm not an electronics guy. I can hold my own when it comes to basic testing, soldering, and replacing of components. Is there a simple way to determine which lead on a transistor is which?

[Krankshaft]

Re: A couple of LCD monitors

I had a Gateway come in just last week with the same problem.

In this case the inverter powered up and showed video for a few seconds and shut down.

What happens is the excess AC ripple because of the bad caps causes the power supply PWM IC to become unstable and shut down.

Replacing the caps fixed it.

The fact that you say Gateway 19" is way to much of a coincidence. Was it made by Hannstar there should be a sticker on the back of the LCD panel?

If so replace the caps with Low ESR ones such as the Panasonic FC series and you're good. Or PM Topcat for some Samxons.