What fails in CCFL inverters?

In the inverter that I have replaced, I have seen the inductors burned up or open.

So I would say that the inductor insulation got hot and shorted between windings.

don

The short between the turns of the transformer is a very common failure.

VLV

It is mostly the TV programs that fail.

the same thing that fails in 15 inch LCD displays.

Very funny. I agree: My TV won't survive another episode of "Lost".

But that's a discussion for another time...

Thanks, guys.

So it looks like they're unrepairable. I'll order one of the replacements.

nothing's unrepairable.

Agreed. But "practicably", cost-effectively, this one is not worth it.

If this was a 60" Panasonic that only needed one inductor wound, and a new PDB was not available, I'd probably think differently.

The transformer seems to be the most common problem. I've only tried to repair about 4 of these. Three were visibly (under a microsocope) burned and probably shorted when the insulation melted between turns. One was open. All were repaired by replacing the transformer (usually cannibalized from a similar LCD inverter).

I've also seen a few with fried switching transistors. However, those were probalby the result of a shorted transformer.

Only once have I seen a dead CCFL tube (that wasn't broken by whomever tried to repair it previously).

At this time, I don't consider it worth the time and effort to repair the inverters. I might if I can't obtain a pull-out repacement on eBay or if the LCD inverter circuitry was built onto the main driver board, as is common on many LCD computah monitors.

Incidentally, I've been tempted to slop some thermally conductive epoxy on the xformer in order to improve the heat dissipation. However, without an IR camera, and more spare time, I haven't bothered.

There are many possible failures. Certainly a shorted transformer is one. Above all, what are the symptoms?

Is it a 'two seconds and then black' problem? Or is it totally dead?

One common problem is shorted drive transistors due to a marginal design. This will result in a blown fuse. Replacing the transistors and fuse is only a temporary fix. Another is shorted transistors due to high ESR on the caps. Replacing the caps, fuse, and transistors is an inexpensive (and nearly permanent) repair. I am using a 21" lcd monitor I recieved 'gratis' after the fuse in the inverter failed for no apparent reason.

There are many ways to fix electronic systems. Replacing the parts that 'usually' fail is one way. It's an expensive way, but it IS a way.

PlainBill

I've seen a surprising number that only had a blown fuse. If the fuse is blown, and there are no other obvious problems, then it's worth trying. Andy Cuffe

snipped-for-privacy@gmail.com

"John E." schreef in bericht news: snipped-for-privacy@news.sf.sbcglobal.net...

Basicly the same that has high failure rate in CRT TV-sets and -monitors: The high voltage components. So the transistors (either bipolair or FET) and the connected coils/transformers. Too often, when one fails, the other is draged along into downfall. As for the transistors some simple measurements with an ohmmeter will often tell the story. Coils however may have an internal short that cannot be found by such an instrument. I found a ringer being usefull although the results tend to be less pronounced then when measuring LOPTs.

petrus bitbyter

Oh yes. Two years ago we walk into the office kitchen, the microwave stopped working. As the resident hands-on guy, I was told to order a new one but I took it apart instead. The fuse was blown and a quick trip to Radio Shack for a ceramic fuse solved that problem. The oven still runs two years on.

It's not about "shotgun repair".

My inquiry re. "usual suspects" is to get an idea of where to start testing (key word: "testing").

For example hearing that the windings frequently go and take the transistors with them, I'll start by looking at:

Fuse, windings, transistors.

Before wading into a swamp, it pays to talk to others who have been there.

On Apr 25, 11:26=A0pm, John E. wrote: > What fails most commonly in inverter circuits in, for example, 18 inch LCD > displays? >

I can't tell you what is a common failure but we had a 17" LCD Viewsonic monitor fail at work last week. Tech opened it up and found a 1000uF 25V cap in the power supply that had bulged / ruptured / peed. It was 1/8" from a heatsink so we mounted the new cap leaned over 90 degrees to inprove clearance and be a little farther from the warm spot. Tha monitor is fine with 1 new $0.29 cap. BTW all the other caps had excellent ESR,

G=B2

John E. wrote in news: snipped-for-privacy@news.sf.sbcglobal.net:

that inductor sounds like a great place to use a flyback tester,like the inexpensive Dick Smith FBT.

Perhaps this is a case of miscommunication. Earlier you posted

I took that (apparently incorrectly) to mean you were going to replace the entire inverter. If indeed you meant you intended to replace any defective transformers (rather than trying to repair them), indeed you are taking the correct approach.

For what it's worth, there are a number of entrepaneurs in the Far East who are eager to sell replacement transformers, transistors, etc at really reasonable prices.

PlainBill

True. Or even the much older yoke and flyback testers of the CRT TV age will do the job.

PlainBill

One common failure in some designs is a chain reaction failure. Poor quality caps are used in the power supply and the inverter. As the ESR rises the drive transistors in the inverter tend to overheat, eventually shorting and blowing the input fuse on the inverter. Replaceing the low quality caps, the transistors, and the fuse results in a working monitor.

The Westinghouse Westinghouse L1975NW (and equivalent Acer model) - identical monitor except for the plastic - have this problem.

PlainBill