What fails in CCFL inverters?

J

John E.

Guest
What fails most commonly in inverter circuits in, for example, 18 inch LCD
displays?

<http://www.lcdrepair.us/1800inverterKUBNKM045A.html>

I know anything *can* fail. But is there a common, high-frequency failure
component in these inverters?

Thanks.
--
John English
 
John E. wrote:
What fails most commonly in inverter circuits in, for example, 18 inch LCD
displays?

http://www.lcdrepair.us/1800inverterKUBNKM045A.html

I know anything *can* fail. But is there a common, high-frequency failure
component in these inverters?

Thanks.
In the inverter that I have replaced, I have seen the inductors burned
Click to expand...
up or open.

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

don
 
"John E." <incognito@xbjcd.com> wrote in message
news:0001HW.C6194C9E007788DCB02149AF@news.sf.sbcglobal.net...
What fails most commonly in inverter circuits in, for example, 18 inch LCD
displays?

http://www.lcdrepair.us/1800inverterKUBNKM045A.html

I know anything *can* fail. But is there a common, high-frequency failure
component in these inverters?
Click to expand...
The short between the turns of the transformer is a very common failure.

VLV
 
On Apr 26, 8:26 am, John E. <incogn...@xbjcd.com> wrote:
What fails most commonly in inverter circuits in, for example, 18 inch LCD
displays?

http://www.lcdrepair.us/1800inverterKUBNKM045A.html

I know anything *can* fail. But is there a common, high-frequency failure
component in these inverters?

Thanks.
Click to expand...
It is mostly the TV programs that fail.

--
John English
Click to expand...
 
"John E." <incognito@xbjcd.com> wrote in message
news:0001HW.C6194C9E007788DCB02149AF@news.sf.sbcglobal.net...
What fails most commonly in inverter circuits in, for example, 18 inch LCD
displays?
Click to expand...
the same thing that fails in 15 inch LCD displays.
 
It is mostly the TV programs that fail.
Click to expand...
Very funny. I agree: My TV won't survive another episode of "Lost".

But that's a discussion for another time...
--
John English
 
Thanks, guys.

So it looks like they're unrepairable. I'll order one of the replacements.
--
John English
 
"John E." <incognito@xbjcd.com> wrote in message
news:0001HW.C619CDF80095D9B4B02149AF@news.sf.sbcglobal.net...
Thanks, guys.

So it looks like they're unrepairable. I'll order one of the replacements.
--
John English
Click to expand...
nothing's unrepairable.
 
nothing's unrepairable.
Click to expand...
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.
--
John English
 
On Sat, 25 Apr 2009 23:26:22 -0700, John E. <incognito@xbjcd.com>
wrote:

What fails most commonly in inverter circuits in, for example, 18 inch LCD
displays?

http://www.lcdrepair.us/1800inverterKUBNKM045A.html

I know anything *can* fail. But is there a common, high-frequency failure
component in these inverters?
Click to expand...
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.


--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
 
On Sun, 26 Apr 2009 08:38:16 -0700, John E. <incognito@xbjcd.com>
wrote:

Thanks, guys.

So it looks like they're unrepairable. I'll order one of the replacements.
Click to expand...
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
 
On Sat, 25 Apr 2009 23:26:22 -0700, John E. <incognito@xbjcd.com>
wrote:

What fails most commonly in inverter circuits in, for example, 18 inch LCD
displays?

http://www.lcdrepair.us/1800inverterKUBNKM045A.html

I know anything *can* fail. But is there a common, high-frequency failure
component in these inverters?

Thanks.
Click to expand...
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

acuffe@gmail.com
 
John E. <incognito@xbjcd.com> wrote in
news:0001HW.C619DD4400996FACB07369AF@news.sf.sbcglobal.net:

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.
Click to expand...
why can't you find an inductor for it?

--
Jim Yanik
jyanik
at
kua.net
 
"John E." <incognito@xbjcd.com> schreef in bericht
news:0001HW.C6194C9E007788DCB02149AF@news.sf.sbcglobal.net...
What fails most commonly in inverter circuits in, for example, 18 inch LCD
displays?

http://www.lcdrepair.us/1800inverterKUBNKM045A.html

I know anything *can* fail. But is there a common, high-frequency failure
component in these inverters?

Thanks.
--
John English
Click to expand...
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
 
On Apr 26, 3:47 pm, Andy Cuffe <acu...@gmail.com> wrote:
On Sat, 25 Apr 2009 23:26:22 -0700, John E. <incogn...@xbjcd.com
wrote:

What fails most commonly in inverter circuits in, for example, 18 inch LCD
displays?

http://www.lcdrepair.us/1800inverterKUBNKM045A.html

I know anything *can* fail. But is there a common, high-frequency failure
component in these inverters?

Thanks.

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

acu...@gmail.com
Click to expand...
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.
 
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
Click to expand...
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.
--
John English
 
On Apr 25, 11:26 pm, John E. <incogn...@xbjcd.com> wrote:
What fails most commonly in inverter circuits in, for example, 18
inch LCD
displays?

http://www.lcdrepair.us/1800inverterKUBNKM045A.html

I know anything *can* fail. But is there a common, high-frequency
failure
component in these inverters?

Thanks.
--
John English
Click to expand...
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˛
 
John E. <incognito@xbjcd.com> wrote in
news:0001HW.C61A99EB00C5A686B02809AF@news.sf.sbcglobal.net:

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

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

--
Jim Yanik
jyanik
at
kua.net
 
On Sun, 26 Apr 2009 23:08:27 -0700, John E. <incognito@xbjcd.com>
wrote:

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

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.
Perhaps this is a case of miscommunication. Earlier you posted
Click to expand...

Thanks, guys.

So it looks like they're unrepairable. I'll order one of the replacements.
--
John English
Click to expand...
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
 
On Sat, 25 Apr 2009 23:26:22 -0700, John E. <incognito@xbjcd.com>
wrote:

What fails most commonly in inverter circuits in, for example, 18 inch LCD
displays?

http://www.lcdrepair.us/1800inverterKUBNKM045A.html

I know anything *can* fail. But is there a common, high-frequency failure
component in these inverters?

Thanks.
One common failure in some designs is a chain reaction failure. Poor
Click to expand...
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
 
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