Fade To Grey (Gateway FPD1800)

[Grinder]

A few years ago I purchased a gateway flat panel LCD monitor. The model
number suggests that its an 18" (as does a ruler,) but I recall it being
billed as a 19" At any rate, it has served well enough.

Early on the monitor developed some spots that weren't as bright as the
rest of the screen. You could see them if you had a constant color
background, but not if there was any sort of pattern. Now, though,
things have gotten worse.

While I was looking at the monitor, part of it became marked less
bright. It is at it's most pronounced at the top edge of the screen,
and fades as you move downward. So, if you were to bring up a solid
white screen, this monitor would make it appears as if you had a grey to
white gradient, top to bottom.

Is there any possible service that would cost less than the $200 to
replace this monitor?

Thanks for your thoughts and considerations.

 

[Paul]

A few years ago I purchased a gateway flat panel LCD monitor. The model
number suggests that its an 18" (as does a ruler,) but I recall it being
billed as a 19" At any rate, it has served well enough.

Early on the monitor developed some spots that weren't as bright as the
rest of the screen. You could see them if you had a constant color
background, but not if there was any sort of pattern. Now, though,
things have gotten worse.

While I was looking at the monitor, part of it became marked less
bright. It is at it's most pronounced at the top edge of the screen,
and fades as you move downward. So, if you were to bring up a solid
white screen, this monitor would make it appears as if you had a grey to
white gradient, top to bottom.

Is there any possible service that would cost less than the $200 to
replace this monitor?

Thanks for your thoughts and considerations.

The parts back there that affect output are the inverter
and the CCFL (cold cathode fluorescent) lamp. The inverter
converts +12VDC to around 1000VAC at 3ma or so. That connects
to the fluorescent lamp. The lamp draws 3 watts total power.

The inverter can run on a couple principles. It can be transformer
based, or piezoelectric based. The piezoelectric version, applies
a voltage to one end of the piezo material, and the mechanical
contractions at that end, cause high voltage electricity to be
generated at the other end. That is where the high voltage comes
out. (The piezo material is similar in concept, to what is used in
a gas barbecue starter.) The output of the piezo is supposed to be
a nice sine wave.

To get a range of contrasts, the inverter can be gated on and off,
at around 100Hz or so. Via pulse width modulation, the width of
the 100Hz enabling signal is varied, to give whatever lamp intensity
the user desires. So the lamp intensity adjustment does not have
to be achieved by varying the voltage across the lamp, but instead,
switching the lamp on an off rapidly.

The CCFL lamp is supposed to have a life of 15000 or 20000 hours.
I get the impression, that inverter failure is more likely than
CCFL failure, but your situation almost sounds like you have
two lamps, and one lamp is failing.

In the past, I have found a couple web sites, that carry replacement
parts. But the odds of getting exactly the same thing as was in
there, are pretty slim. Chances are you'll get a "nearest substitute",
if you were to order something. And the thing is, the lamp and
inverter are matched to one another. While you can attempt a
repair with new parts, there is no guarantee you'll get as
many years from the thing when you are finished.

Sometimes, a repair can be as simple as disassembling the connectors
on the inverter and lamp, and then reconnecting them. If the screen
goes dark, it could be a bad connection. But since your light
output seems to be steadily dropping, that almost suggests a lamp
failure. So maybe in your case, you'll actually have to order
replacement parts.

If you only have one monitor, I'd buy a replacement monitor first,
and that will leave you time for "surgery" and contemplation of the
symptoms.

Since there is high voltage in there, I don't recommend running the
thing with the parts sitting on the table. The inverter sine wave
might be at 70KHz or so (plus being gated at 100Hz), and at higher
frequencies, high voltage tends to travel on the surface of your skin.
That means you *might* get less sensation from touching it while it is
operating. But I'm not going to be the person to test that hypothesis.
(The only practical experience I've had with HF HV, is with a Tesla
coil, and that was painless. The resonant frequency of one of those, is
about 200KHz or so.)

Example of a spare parts site:
http://www.lcdpart.com/doc/ccfl.html

Here is an example of a DIY repair project. Some projects
are simpler than this one.
http://www.dnd.utwente.nl/~grit/backlight/ccft.html

Paul

 

[Grinder]

Paul wrote:
[snip]

Thanks for the great info. Your description does sound valid to me--it
looks as I would expect it would if the top tube is not function.
Overall brightness is down by about half--getting more severe the close
you get to the top edge.

One question though:

In the past, I have found a couple web sites, that carry replacement
parts. But the odds of getting exactly the same thing as was in
there, are pretty slim. Chances are you'll get a "nearest substitute",
if you were to order something. And the thing is, the lamp and
inverter are matched to one another. While you can attempt a
repair with new parts, there is no guarantee you'll get as
many years from the thing when you are finished.

Does this mean that I would have to buy the lamp or and inverter as a
matched set, or just that if I buy the lamp it *might not* match my
existing inverter, or not have the typical lifespan?

Thanks again for your thoughtful response.

 

[Paul]

Paul wrote:
[snip]

Thanks for the great info. Your description does sound valid to me--it
looks as I would expect it would if the top tube is not function.
Overall brightness is down by about half--getting more severe the close
you get to the top edge.

One question though:

In the past, I have found a couple web sites, that carry replacement
parts. But the odds of getting exactly the same thing as was in
there, are pretty slim. Chances are you'll get a "nearest substitute",
if you were to order something. And the thing is, the lamp and
inverter are matched to one another. While you can attempt a
repair with new parts, there is no guarantee you'll get as
many years from the thing when you are finished.

Does this mean that I would have to buy the lamp or and inverter as a
matched set, or just that if I buy the lamp it *might not* match my
existing inverter, or not have the typical lifespan?

Thanks again for your thoughtful response.

The lamp might not match your existing inverter. I'm not familiar enough
with defacto standards in this area, to say whether there are common
design points for this stuff. Like whether one manufacturer's 17"
lamp module, is roughly equivalent to another manufacturer's version.
It just seems, if you go to a web site looking for parts, you are
getting a "nearest substitute", and who knows whether it is correct
or not.

I did just find a datasheet for an inverter controller. So, it does seem
that the transformer based inverters, can use closed loop feedback to
control the lamp. This would make the situation less sensitive to the
part substitution (up to the point that the inverter feels it is
overloaded).

http://web.archive.org/web/20040205053740/www.analogmicro.com/Datasheet/ame9001.pdf

This is an example of a controller for piezo based modules. This datasheet
is a wealth of info. I particularly like the description where is says
"If the input voltage were increased to 10 VRMS, the output would
reach 4 kVRMS and possibly crack the PZT transformer." So having a
controller that detects an open lamp, sounds like a good feature
to have This particular device doesn't seem that sophisticated,
and perhaps there are better ones than this one, on the TI web site.
The inverters that are piezo based, are a bit thinner than the
transformer based ones.

http://focus.ti.com/lit/ds/symlink/ucc2977.pdf

I found refs to those devices, via using mouser.com and
entering "CCFL backlight controller" in their search box.

If a substitute lamp is reasonably cheap, you could consider trying
a repair yourself. You might want to replace both lamps, to try to
get the intensity to be the same on both halves of the screen. But also
try just reseating the connectors, in case this is caused by a bad
connector. Also, swapping the lamps around, to see if the problem
follows the lamp, or follows the socket, may provide you with
more info as to what is busted.

Paul

 

[Grinder]

If a substitute lamp is reasonably cheap, you could consider trying
a repair yourself. You might want to replace both lamps, to try to
get the intensity to be the same on both halves of the screen. But also
try just reseating the connectors, in case this is caused by a bad
connector. Also, swapping the lamps around, to see if the problem
follows the lamp, or follows the socket, may provide you with
more info as to what is busted.

Thanks again Paul, will do.

 

[kony]

Thanks again Paul, will do.

To retain matching, I would replace both (presuming only 2
installed) tubes, not just the one that seems failed.

 

[Grinder]

A few years ago I purchased a gateway flat panel LCD monitor. The model
number suggests that its an 18" (as does a ruler,) but I recall it being
billed as a 19" At any rate, it has served well enough.

Early on the monitor developed some spots that weren't as bright as the
rest of the screen. You could see them if you had a constant color
background, but not if there was any sort of pattern. Now, though,
things have gotten worse.

While I was looking at the monitor, part of it became marked less
bright. It is at it's most pronounced at the top edge of the screen,
and fades as you move downward. So, if you were to bring up a solid
white screen, this monitor would make it appears as if you had a grey to
white gradient, top to bottom.

Ok, so I've taken Paul's suggestion and have swapped the two CCFL's in
this panel (it's an LG LM181E3 (A2) by the way.) The symptoms remain
exactly the same--normal brightness at the bottom of the screen, but
fading out as you approach the top edge.

From my extensive experience (2-3 messages in this newsgroup and a
shiny screwdriver,) I'm speculating that this means one of the inverters
has gone bad. I've searched a bit for a replacement, but haven't had
any luck. Unfortunately, I'm not very optimistic there, because I have
to meet two criteria for the replacment:

1) It has to be electrically compatible with an LG LM181E3 (A2) panel

2) It has to be mechanically compatible with the FPD1800 case

There's not much extra room in the FPD1800's case, so I fear that even
if I find something that meets criteria 1, the second requirement will
present a problem.

Although I am now inclined to purchase a new screen, I would not pass up
an opportunity to inexpensively recoup my exiting monitor. Any
corrections to my thinking or new ideas towards that goal would be
greatly appreciated. Thanks (Paul and kony) for your considerations,
already rendered, on the matter.