What fails in CCFL inverters?
John E.
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
don
up or open.
So I would say that the inductor insulation got hot and shorted between
windings.
don
Vladimir Vassilevsky
"John E." <inco...@xbjcd.com> wrote in message
news:0001HW.C6194C9E...@news.sf.sbcglobal.net...
The short between the turns of the transformer is a very common failure.
VLV
pant...@gmail.com
It is mostly the TV programs that fail.
> --
> John English
Lynn
> displays?
>
the same thing that fails in 15 inch LCD displays.
John E.
Very funny. I agree: My TV won't survive another episode of "Lost".
But that's a discussion for another time...
--
John English
John E.
So it looks like they're unrepairable. I'll order one of the replacements.
--
John English
Lynn
nothing's unrepairable.
John E.
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
Jeff Liebermann
wrote:
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 je...@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
PlainBill
wrote:
>Thanks, guys.
>
>So it looks like they're unrepairable. I'll order one of the replacements.
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
Andy Cuffe
wrote:
>What fails most commonly in inverter circuits in, for example, 18 inch LCD
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
petrus bitbyter
"John E." <inco...@xbjcd.com> schreef in bericht
news:0001HW.C6194C9E...@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
a7yvm1...@netzero.com
> On Sat, 25 Apr 2009 23:26:22 -0700, John E. <incogn...@xbjcd.com>
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.
John E.
> 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.
--
John English
stra...@yahoo.com
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,
G²
Jim Yanik
that inductor sounds like a great place to use a flyback tester,like the
inexpensive Dick Smith FBT.
--
Jim Yanik
jyanik
at
kua.net
PlainBill
wrote:
>> There are many ways to fix electronic systems. Replacing the parts
Perhaps this is a case of miscommunication. Earlier you posted
>>Thanks, guys.
>>
>>So it looks like they're unrepairable. I'll order one of the replacements.
>>--
>>John English
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
PlainBill
True. Or even the much older yoke and flyback testers of the CRT TV
age will do the job.
PlainBill
PlainBill
wrote:
>What fails most commonly in inverter circuits in, for example, 18 inch LCD
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
Jim Yanik
news:tdrbv4lmlso3vcggu...@4ax.com:
> On Sat, 25 Apr 2009 23:26:22 -0700, John E. <inco...@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
> 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.
the TEK 1720,1730 NTSC TV waveform monitors had this problem,except all the
other supplies would rise,the HV xstr would overheat,burn the PCB until it
became conductive,and then put the switcher into 'click' mode.I used to
Dremel out the carbonized part,fill with epoxy,and put down new runs and
eyelets,and changed the +5V filter cap to a better grade and a larger
capacitance value.Never had any repeats after that.
> 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
>
--
Charlie E.
wrote:
>> It is mostly the TV programs that fail.
>
>Very funny. I agree: My TV won't survive another episode of "Lost".
>
>But that's a discussion for another time...
Speaking of failing TVs... 8-)
My old Zenith 25" TV has been doing the oddest thing. The menus are
going crazy, like someone was randomly hitting the menu button on my
remote. The menus pop up, start changing different values, go here
and there throughout the menu tree. It drives me crazy to try and
watch it! My wife doesn't mind, though... ;-)
Any ideas what could be causing it? At first, I thought it might be a
remote problem, or even a remote interaction problem, but it doesn't
look like it. I even to out the batteries to all the remotes, and
covered the IR receiver window, but it still kept going crazy. My
only thought is some sort of fault on the logic board, or something.
Charlie
Michael A. Terrell
Ask on news:sci.electronics.repair Give them the model number or
chassis number.
--
You can't have a sense of humor, if you have no sense!
John E.
Rule 1 (or is it 4...?) of news groups: do not hijack a thread.
If you want to ask another question, please start your own thread.
Cheers,
--
John English
John E.
> 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
-=-=-=-
In case anyone watching was wondering, this is what I was looking for.
Knowing what *might* be the modus operandi of this monitor is a huge leg up
on the attack for a non-pro such as myself.
Thanks, PB! And to all the others who pitched in.
--
John English
Jim Yanik
news:hkccv4te77bdf8g96...@4ax.com:
probably bad electrolytic caps.
perhaps one or more of your LV supplies is getting out of spec,and
affecting the logic ICs.
PlainBill
wrote:
>> One common failure in some designs is a chain reaction failure. Poor
Paying it forward, one technique I have been known to use is to look
up the data sheet and any application notes of the major components on
an electronic assembly. In the case of an inverter, the PWM
controller IC is of major interest. The application notes usually
include a full schematic of an inverter. Quite often they also
include the calculations used to design the inverter.
One problem with the typical Chinese made monitors is no rigorous
analysis of the design has been made. One popular inverter design
included a pair of FETs in series from the positive power rail to
ground, with the primary of the transformer connected to the junction
between the two. Someone smarter than I dissected the circuit and
realized there was no provision to limit the current through the two
FETs if both were gated on at the same time. In addition, the circuit
driving the gates featured a resistor which (due to the capacitance of
the gates) would result in both FETs being on for a significant time
on every switching cycle. One could say the design was designed to
fail.
PlainBill
Bob Larter
I'd look at the PCB & caps around the IR receiver. IR receivers are also
very sensitive to RF, so you could get erroneous operation if there's
something wrong with the shielding or grounding around the module.
[sci.electronics.repair added]
--
W
. | ,. w , "Some people are alive only because
\|/ \|/ it is illegal to kill them." Perna condita delenda est
---^----^---------------------------------------------------------------
John E.
equivalent Acer model.)
Update on the inverter PCB repair:
Checked electrolytic caps for ESR; all were good, better than suspected.
Checked transistors for shorts and found none. SMD fuse was blow so I
replaced it.
Now when the display is powered on, the backlight comes on for 1 second then
goes off. The Power indicator (in the On switch) acts normal (no blinking
error codes, etc.).
Any idea what might cause this symptom?
Thanks,
--
John English
Steve Sousa
"John E." <inco...@xbjcd.com> wrote in message
news:0001HW.C62253AC...@news.sf.sbcglobal.net...
The HV transformer. Power it in a dark room, you'll probably see it spark.
John E.
So I just kept cycling power and... it has been powered on for over 2 hours
now with no problems.
I'm beginning to suspect the electrolytic caps. Being el-cheepo (no-name)
brand, they probably went intermittent short or low ESR and blew the fuse.
After replacing the fuse (remember it's been over a year since this thing has
been powered on for more than a few seconds at a time) the caps needed a
little time to reform.
Or maybe a power surge popped the fuse (and the cap re-form thing still
applies).
I think I'll replace the caps -- for peace of mind -- and see if it continues
to work.
--
John English
Ken
> > The HV transformer. Power it in a dark room, you'll probably see it spark.
>
> So I just kept cycling power and... it has been powered on for over 2 hours
> now with no problems.
>
> I'm beginning to suspect the electrolytic caps. Being el-cheepo (no-name)
> brand, they probably went intermittent short or low ESR and blew the fuse.
High ESR !
John E.
Doh!!
Yes, of course.
(Homer answer: "Oh, so maybe I shouldn't have replaced all those good caps?"
;-)
--
John English
John E.
>> 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
> In case anyone watching was wondering, this is what I was looking for.
> Knowing what *might* be the modus operandi of this monitor is a huge leg up
> on the attack for a non-pro such as myself.
>
> Thanks, PB! And to all the others who pitched in.
Just to follow up...
Replaced all the caps (using Panasonic FM series) in this monitor and it
works like new. And should last quite a bit longer.
--
John English
Bob Larter
Thanks for passing on your results, John. It's always nice to know how
these things turn out.
John E.
> these things turn out.
I concur. It's all-too-common to follow such a thread that is years old only
to find no-one cared to post the results. I like to think about the guy or
gal who is Googling a few years from now and comes across this thread. (Hi!)
;-)
--
John English
Rich Grise
Speaking of that, what ever happened to the self-tuning piano? Was that
guy ever going to post a .WAV file or something, of the piano tuning
itself?
Thanks,
Rich
Bob Myers
> Speaking of that, what ever happened to the self-tuning piano? Was
> that guy ever going to post a .WAV file or something, of the piano
> tuning itself?
I believe it turned out that the only existing documentation
of the self-tuning piano in action was in the form of miniature
photographs stored as multiple images on a common sheet
of film, and these proved impossible to correctly adjust for
conversion into any electronic media. For as we all know,
while you CAN tune a piano, you can't tune a fiche.
Bob M.
Rich Webb
Well played, sir!
--
Rich Webb Norfolk, VA
Dave Platt
<CurlyHoward>
Ngung, ngung, ngung!!
</CurlyHoward>
--
Dave Platt <dpl...@radagast.org> AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!
Spehro Pefhany
Not *alone*, certainly, but perhaps if you had a tuner helper...
Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
sp...@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
Rich Grise
> On Tue, 2 Jun 2009 12:01:51 -0600, the renowned "Bob Myers"
>>
>>> Speaking of that, what ever happened to the self-tuning piano? Was
>>> that guy ever going to post a .WAV file or something, of the piano
>>> tuning itself?
>>
>>I believe it turned out that the only existing documentation
>>of the self-tuning piano in action was in the form of miniature
>>photographs stored as multiple images on a common sheet
>>of film, and these proved impossible to correctly adjust for
>>conversion into any electronic media. For as we all know,
>>while you CAN tune a piano, you can't tune a fiche.
>
Don't hire Oppornockity!
For, as we all know, Oppornickity tunes but once. ;-)
Cheers!
Rich