CRT monitor getting brighter over time
Wiebe Cazemier
My Eizo T766 CRT monitor has been turning brighter for years, ever since I got
it. I used to be able to correct it using the cut-off and gain controls in the
on screen menu, but the red had reached 0%, so I was out of lee-way.
Therefore, I resorted to adjusting the flyback transformer.
Anyway, my question is, what could be causing a monitor to turn brighter? Every
other monitor I know turns darker over time.
And on a sidenote, when calibrating the flyback transformer, what voltage is it
you're adjusting? Acceleration voltage?
Regards,
Wiebe Cazemier
JANA
actual fact, it must be within a specific spec range. The tube bias settings
must be set to make the cut-off for each colour-gun in the tube properly
track and work within proper range. On most monitors manufactured after
1994, most of these settings are done through a specific service set-up and
manufacture software using their dedicated hardware interface for the
particular monitor.
Obviously some component or device is going defective, thus causing the
brightness to be changed. Many times, I found the HV multiplier to be the
fault. Sometimes, it has been other types of components in the bias and
drive circuits that work with the CRT.
If there is adequate range, you can try to turn down the G2 bias on the HV
module. This will only be a temporary fix. The characteristics of the colour
tracking and the black cut-off levels will be most likely be changed when
this control is adjusted.
I would be seriously considering to get a new LCD panel at this point. You
will find it superior to an old CRT monitor.
--
JANA
_____
"Wiebe Cazemier" <half...@gmx.net> wrote in message
news:43406$47710cdc$d4cc82be$8...@cache2.tilbu1.nb.home.nl...
dak...@myway.com
manual.
The monitor must be on for a minimum of 60 minutes, no screen saver or
power save mode, in order for this option to come up.
This will compensate for the wear on the picture tube if you did not
wait too long to run it.
http://www.eizo-downloads.com/downloads/manuals/index.php
Wiebe Cazemier
> You need to run the color restoration as shown on page 16 of the user
> manual.
> The monitor must be on for a minimum of 60 minutes, no screen saver or
> power save mode, in order for this option to come up.
> This will compensate for the wear on the picture tube if you did not
> wait too long to run it.
>
> http://www.eizo-downloads.com/downloads/manuals/index.php
Do you think I would know how to adjust the flyback transformer but not know
about this feature... :)? It didn't compensate for the overly bright image.
Wiebe Cazemier
> The adjustment on the HV multiplier is the G2 or screen grid voltage. In
> actual fact, it must be within a specific spec range. The tube bias settings
> must be set to make the cut-off for each colour-gun in the tube properly
> track and work within proper range. On most monitors manufactured after
> 1994, most of these settings are done through a specific service set-up and
> manufacture software using their dedicated hardware interface for the
> particular monitor.
>
> Obviously some component or device is going defective, thus causing the
> brightness to be changed. Many times, I found the HV multiplier to be the
> fault. Sometimes, it has been other types of components in the bias and
> drive circuits that work with the CRT.
>
> If there is adequate range, you can try to turn down the G2 bias on the HV
> module. This will only be a temporary fix. The characteristics of the colour
> tracking and the black cut-off levels will be most likely be changed when
> this control is adjusted.
I had already changed the bias on the HV module. When I did so, the image
looked somewhat bluish. I ran the the automatic color restoration feature,
which dkuhajda mentioned, and everything was corrected. The reference image I
created to calibrate cut-off and gain of each individual color shows a perfect
image.
BTW, the automatic color restoration never seemed to have done anything in the
past. But after changing the HV bias, it did work (I could see it do things it
never did before).
BTW2, I don't think some component is going bad. It's not as if it started
doing this suddenly. In the course of the 4 years that I've had it, it slowly
turned brighter.
Also, the HV bias is very touchy. When I turned it down just a tad without
looking at the screen, it went completely black. Could it be possible that for
some reason, like heat contraction/expansion, the HV bias control changed
gradually?
>
> I would be seriously considering to get a new LCD panel at this point. You
> will find it superior to an old CRT monitor.
>
This is the last 19" CRT Made by Eizo, using a Sony Trinitron apature grill
tube; it's one of the best CRT's out there. I bought it in 2003. And I find
the image quality far, far superior to any TFT I've seen. It still works
perfectly, besides the screen slowly getting brighter (which is fixed for
now).
I don't like TFT and I will never get one, if possible. I don't like the
concept of backlights, I don't like the concept of dithering 18 bit color to
produce 16.2 milion (not 16.7 as true 24 bit would be), I don't like native
resolutions inherent in low-DPI fixed pixel displays, etc.
James Sweet
I didn't know my monitor had this feature until relatively recently, and I
had already been inside it searching for a screen adjustment on the flyback.
Ended up needing the Sony DAS software to get everything where it should be
though.
Jamie
Don't you get it?
It's not what you like and what you want!
It's what they want you to have and you will like it. You
will have one regardless the price they dictate and pay it!
And wait, that's not all. After you are forced into giving them
your money for something you don't want. It'll be obsolete just after
you walk out the store and repairs will be many times more than just
going though the same ordeal again which they will so condition you
to adhere too!
Btw.
Have a great Xmas!
--
"I'd rather have a bottle in front of me than a frontal lobotomy"
Wiebe Cazemier
You needed the Sony software after the adjustment on the flyback?
Wiebe Cazemier
> Don't you get it?
>
> It's not what you like and what you want!
>
> It's what they want you to have and you will like it. You
>
> will have one regardless the price they dictate and pay it!
>
> And wait, that's not all. After you are forced into giving them
> your money for something you don't want. It'll be obsolete just after
> you walk out the store and repairs will be many times more than just
> going though the same ordeal again which they will so condition you
> to adhere too!
Sadly, you are correct. The industry needed something new. And unfortunately,
most people want these TFT screens because of their small size. The real
high-end user has to suffer for the ignorance of the masses. It amazes me how
much effect the appearance of the actual machine has on the quality of the
screen, for most people. I could write an entire essay about that subject...
Luckily, these Eizo screens are made to last. With the calibration features it
offers, the picture's is as good as new after 14608 hours of use. A low-end
monitor would almost have reached its MTBF by now...
With some luck, SED screens are available when this monitor dies. The
technology exists, but there are license issues. SED is still a fixed pixel
grid, but at least works on the basis of color addition (like your eyes!) as
opposed to color polarization and subtraction.
BTW, I just watched some DVD on this screen. The absolute blackness this
monitor offers is SO important for the image quality. As soon as the slightest
bit of grey starts to leak through, the entire image quality suffers; it just
looses its feel. It's as if you throw a bucket of paint over a Van Gogh... I
always compare backlight bleeding to noise in audio. For some reason, people
dispise the latter, but accept the former...
>
> Btw.
> Have a great Xmas!
Same to you. Bet you got a TFT screen for christmas :)
James Sweet
There is no adjustment on the flyback, or any other internal controls. It's
all done by software.
Jerry G.
to correct the fault you are describing. In most monitors it is part of
the flyback assembly. On the odd occasion, I have had CRT's starting to
go defective to also cause this problem.
Personally, I would consider changing the monitor for a good LCD type.
Then you will be good for a number of years without any problems.
--
Jerry G.
"Wiebe Cazemier" <half...@gmx.net> wrote in message
news:c0c3f$47715c1b$d4cc82be$13...@cache1.tilbu1.nb.home.nl...
Wiebe Cazemier
> When I used to service monitors, I changed many of these HV multipliers
> to correct the fault you are describing. In most monitors it is part of
> the flyback assembly. On the odd occasion, I have had CRT's starting to
> go defective to also cause this problem.
In these monitors, what exactly is going bad? The HV multiplier is nothing but
a bunch of copperwire wrapped around some core, right? How can that wear
down...?
>
> Personally, I would consider changing the monitor for a good LCD type.
> Then you will be good for a number of years without any problems.
>
No flame intended, but I really don't understand why people are advising me to
get a new TFT screen. The issue I described is a very minor. The drift has
been so slow that every few months the colors needed a bit of calibration. The
colors are still extremely pure, black is pitch black, white is brightly
white, the image is sharp, high voltage regulation is perfect (so the image is
stable under all brightness conditions, RGB convergence is good, etc. In other
words, it displays a perfect picture.
Even if you didn't dispise TFT's like I do (see my other posts), you would be
mad to replace this screen only because the HV bias needed a minor
adjustment... If it were 10 or 15 years old, perhaps there would be some logic
to it, but after 4 years of use and the MTBF not reached by a long shot...?
Wiebe Cazemier
> There is no adjustment on the flyback, or any other internal controls. It's
> all done by software.
I thought all flybacks had adjustment controls nowadays. I guess then I'm lucky
this monitor still had them, seeing as how it's the most modern CRT every
made.
William Sommerwerck
> On Wednesday 26 December 2007 04:11, Jerry G. wrote:
>> When I used to service monitors, I changed many of these HV
>> multipliers to correct the fault you are describing. In most monitors
>> it is part of the flyback assembly. On the odd occasion, I have had
>> CRT's starting to go defective to also cause this problem.
> In these monitors, what exactly is going bad? The HV multiplier is
> nothing but a bunch of copper[ ]wire[s] wrapped around some core,
> right? How can that wear down...?
You're confusing voltage multipliers with transformers.
William Sommerwerck
> Luckily, these Eizo screens are made to last. With the calibration
> features it offers, the picture's is as good as new after 14608 hours
> of use. A low-end monitor would almost have reached its MTBF by
> now...
Is a ViewSonic a low-end monitor? Mine is about 5 years old, gets two to
three hours' (at least) use each day, and is running fine. I have no
intention of buying an LCD display until this monitor fails (or I buy my
next computer).
There was a time when Eizo was pretty much _the_ monitor to own. It is not
longer a highly visible brand, at least not in the US.
> With some luck, SED screens are available when this monitor dies.
> The technology exists, but there are license issues.
The current consensus is that the license issues will not be resolved and we
will never see SED displays.
I've wondered why we haven't seen much in the plasma-based computer
displays. I can think of a number of reasons, including limited resolution
for a given screen size and significantly higher power consumption.
> SED is still a fixed pixel grid, but at least works on the basis of color
> addition (like your eyes!) as opposed to color polarization and
subtraction.
Way incorrect.
All current LCDs use additive color. Some years back there were LCD panels
for transparencey projectors that used subtractive synthesis. This allowed
significantly higher resolution, but had no other advantage I can think of.
If you want to get picky about it, subtractive systems are "additive" in
that (for example) the yellow layer -- and only the yellow layer -- controls
the amount of blue light in the image. The blue light passed by the yellow
layer is "added" to the green light passed by the magenta layer and the red
light passed by the cyan layer. (This is all semantics, of course. I'm
making a point, not trying to "prove" something.)
I have no idea what you mean by "color polarization". The polarized layers
in an LCD are _not_ used to create colors (such as the colors seen when
placing plastics between crossed polarizers).
jango2
> other monitor I know turns darker over time.
Defective 200V line electrolytic filter capacitor?.
Reduced capacitance due to drying electrolyte.
Doesn't charge to 180 or 200 volts anymore causing lower cathode
voltages thereby driving beam current up.
Usually a 22uF/250V.
Merry Xmas
Jango
Wiebe Cazemier
> Is a ViewSonic a low-end monitor? Mine is about 5 years old, gets two to
> three hours' (at least) use each day, and is running fine. I have no
> intention of buying an LCD display until this monitor fails (or I buy my
> next computer).
I don't know much about ViewSonic. It's not, or hardly, available here. But
with low-end, I meant the cheapest models. I have a Philips 105S here, which
is one of those. Image quality has degraded significantly over the three years
I used it.
This Eizo monitor has been running about 12 hours per day or more (I work at
home) for the last few years. The hours of use I mentioned can be found in the
OSD menu.
>
> There was a time when Eizo was pretty much _the_ monitor to own. It is not
> longer a highly visible brand, at least not in the US.
I would agree. Their TFT screens are no better than others I've seen. As for
CRT, it's a long story, but I tried several T766 models and this one was the
only one without grave convergence errors. Philips high-end CRT range also
suffered from major convergence problems (I had tried 6 different 109p40's
before giving up and going for this Eizo...).
But, now that I have this specific one, I'm glad I have it. It still has
the "Eizo Legacy" of quality... Not just in image quality, but also in
features. I've never seen another monitor which allows you to set the color
cut-off in the OSD menu, for example. It could be that there are, but I've
never seen one :)
> I've wondered why we haven't seen much in the plasma-based computer
> displays. I can think of a number of reasons, including limited resolution
> for a given screen size and significantly higher power consumption.
Don't plasma screens wear down very rapidly? Computerscreens are used more than
TV's, mostly, so perhaps that's the reason? Or, more likely, they want to
exploit the investments made for TFT as much as possible. It's better for them
to wait with the introduction of a new technology.
> Way incorrect.
>
> All current LCDs use additive color. Some years back there were LCD panels
> for transparencey projectors that used subtractive synthesis. This allowed
> significantly higher resolution, but had no other advantage I can think of.
>
> If you want to get picky about it, subtractive systems are "additive" in
> that (for example) the yellow layer -- and only the yellow layer -- controls
> the amount of blue light in the image. The blue light passed by the yellow
> layer is "added" to the green light passed by the magenta layer and the red
> light passed by the cyan layer. (This is all semantics, of course. I'm
> making a point, not trying to "prove" something.)
>
> I have no idea what you mean by "color polarization". The polarized layers
> in an LCD are _not_ used to create colors (such as the colors seen when
> placing plastics between crossed polarizers).
As it says at [1]: "LCD technology is based on the properties of polarized
light (...) When an LCD pixel darkens, it polarizes at 90 degrees to the
polarizing screens.". However, it could be that I've got stuff mixed up. I do
know that wearing polarized sunglassed can make an LCD display (like on a
watch) unreadable, but I've never tried it on a TFT LCD screen.
As for the subtraction; the process of creating color in TFT screens starts
with white light, which is then turned into the desired color. I call that
subtraction. It may not be literal subtraction from the point of view of the
sub pixel, but I do think this idea is principally flawed. You cannot make
monochromatic light for the RGB colors that way. The phosphor photon-emission
of a CRT comes much closer, if not completely.
Anyway, you seem to know more about TFT screens that I do, but that doesn't
take away the fact that I don't like them ;). Image quality is just too poor,
and the manufacturers cheat to get higher specs, and those cheats are visible.
[1] http://en.wikipedia.org/wiki/Liquid_crystal_display_television
Wiebe Cazemier
> Defective 200V line electrolytic filter capacitor?.
> Reduced capacitance due to drying electrolyte.
> Doesn't charge to 180 or 200 volts anymore causing lower cathode
> voltages thereby driving beam current up.
> Usually a 22uF/250V.
> Merry Xmas
> Jango
Drying electrolyte is consistent with the from-the-start slow increase in
brightness. Also, I've seen a lot of devices with leaking caps, so they are
quite notorious.
BTW, how exactly is the beam current driven up when the voltage decreases? I
would have expected it to be the other way around.
William Sommerwerck
> As for the subtraction; the process of creating color in TFT screens
starts
> with white light, which is then turned into the desired color. I call that
> subtraction.
Not in the usual sense. LCDs work by "adding" individual R, G, and B pixels.
A true subtractive panel would have cyan, magenta, and yellow layers.
> It may not be literal subtraction from the point of view of the sub-
> pixel, but I do think this idea is principally flawed. You cannot make
> monochromatic light for the RGB colors that way. The phosphor
> photon-emission of a CRT comes much closer, if not completely.
Phosphors aren't monochromatic, either.
James Sweet
> Is a ViewSonic a low-end monitor? Mine is about 5 years old, gets two to
> three hours' (at least) use each day, and is running fine. I have no
> intention of buying an LCD display until this monitor fails (or I buy my
> next computer).
>
> There was a time when Eizo was pretty much _the_ monitor to own. It is not
> longer a highly visible brand, at least not in the US.
>
>
Viewsonic is a mid range monitor, I've had a few of them and they provide
good performance for the price, but there's better monitors out there. Some
models were very prone to failure, I replaced at least half a dozen
optocouplers in the power supplies, they would fail slowly and cause the
voltage to creep up until it blew the vertical output IC.
Eizo monitors are really excellent. I recently repaired a 14 year old Nanao
(former name of Eizo) monitor my mom has, a few new capacitors and it has a
razor sharp image, it's still perfectly serviceable.
TFT monitors are good for laptops, and anywhere space is critical, I have a
nice big one at work which does look pretty good, but the flat Sony CRT I
have at home is far superior to my eyes.
Mr. Land
PMFJI....
> BTW2, I don't think some component is going bad. It's not as if it started
> doing this suddenly. In the course of the 4 years that I've had it, it slowly
> turned brighter.
Which would suggest that the value of one or more components is slowly
drifting due to heat/age/leaks/etc.
> BTW, how exactly is the beam current driven up when the voltage decreases? I
> would have expected it to be the other way around.
Lower cathode voltage == larger potential between cathode and plate
==> more current.
William Sommerwerck
news:Hdxcj.17001$HQ6.9429@trndny01...
> Viewsonic is a mid range monitor, I've had a few of them and they provide
> good performance for the price, but there's better monitors out there.
Some
> models were very prone to failure, I replaced at least half a dozen
> optocouplers in the power supplies, they would fail slowly and cause the
> voltage to creep up until it blew the vertical output IC.
The ViewSonic I have is unbelievably good. It uses a Mitsubishi Diamondtron
tube, and the convergence and purity are "perfect" right to the corners. I
used to own Sonys, and they were never that good.
JANA
number of high voltage capacitors, diodes and resistor combinations to
multiply the voltage from the flyback. There are tap-offs for the focus
supply, screen supply, and the high voltage for the CRT anode. Because
feedback regulation is required, the HV multiplier in your TV set can be
fairly sophisticated. There can be a fair number of components involved.
The flyback is really a high voltage; high speed switching transformer with
a number of secondaries and usually a single primary. The HV multiplier is
usually combined together as part of the flyback assembly.
A very basic idea of how a high voltage multiplier is constructed:
http://www.rmcybernetics.com/images/main/pyhsics/voltage_multiplier_schematic_diagram.jpg
http://www.spellmanhv.com/tech/images/an_08a.jpg
--
JANA
_____
"Wiebe Cazemier" <half...@gmx.net> wrote in message
news:acb33$47724392$d4cc82be$20...@cache5.tilbu1.nb.home.nl...
Wiebe Cazemier
> The HV multiplier is more complicated than just wires. It consists of a
> number of high voltage capacitors, diodes and resistor combinations to
> multiply the voltage from the flyback. There are tap-offs for the focus
> supply, screen supply, and the high voltage for the CRT anode. Because
> feedback regulation is required, the HV multiplier in your TV set can be
> fairly sophisticated. There can be a fair number of components involved.
>
> The flyback is really a high voltage; high speed switching transformer with
> a number of secondaries and usually a single primary. The HV multiplier is
> usually combined together as part of the flyback assembly.
>
>
> A very basic idea of how a high voltage multiplier is constructed:
>
>
http://www.rmcybernetics.com/images/main/pyhsics/voltage_multiplier_schematic_diagram.jpg
>
> http://www.spellmanhv.com/tech/images/an_08a.jpg
I detect some cognitive disconance on my part. I work a lot with audio and
other low voltage electronics, and the full wave and half wave rectifiers are
quite common, and I can see it's the same thing. That is, as far as the basics
go.
jango2
> would have expected it to be the other way around.
Potential difference between a cathode and final anode increases
when ;
1) Final anode voltage goes up OR
2) Cathode voltage (normally held at 180 or 200) is decreased
Cheers!
Dave W
defocussed, but comes right after about half an hour. The effect can
be corrected by adjusting the screen and focus pots, but after warmup
it's too bright and defocussed. The screen and focus controls are
tapped off a potential divider from the EHT, inside the output
transformer assembly. The resistance to earth at the screen output
(probably about 500V) is 17M ohms, so the resistance at the top (25kV
EHT) must be in the region of 800M. My theory is that this resistance
is unstable. I would need a new output assembly costing about £25 to
repair it.
James Sweet
"Dave W" <dave...@yahoo.co.uk> wrote in message
news:61b48aec-3016-4941...@w38g2000hsf.googlegroups.com...
I have a Panasonic CRT TV with a similar problem. It comes on dark and
defocussed, but comes right after about half an hour. The effect can
be corrected by adjusting the screen and focus pots, but after warmup
it's too bright and defocussed. The screen and focus controls are
tapped off a potential divider from the EHT, inside the output
transformer assembly. The resistance to earth at the screen output
(probably about 500V) is 17M ohms, so the resistance at the top (25kV
EHT) must be in the region of 800M. My theory is that this resistance
is unstable. I would need a new output assembly costing about £25 to
repair it.
On 25 Dec, 13:59, Wiebe Cazemier <halfg...@gmx.net> wrote:
>
>
I suspect bad capacitors, that's the usual cause of things changing as they
warm up. It could be affecting power supply voltage.
b
>
> I suspect bad capacitors, that's the usual cause of things changing as they
> warm up. It could be affecting power supply voltage.
in both of these cases i would start by changing the cap in the RGB
output and b+ stages. i have cured many faults this way. the caps are
usually rated 160 v or more and has a low value - between 4.7 and 47
uF in my experience.
Wiebe Cazemier
> in both of these cases i would start by changing the cap in the RGB
> output and b+ stages. i have cured many faults this way. the caps are
> usually rated 160 v or more and has a low value - between 4.7 and 47
> uF in my experience.
For now, the monitor is working perfectly, but I'll keep it in mind.
Are there others ways I can recognize those caps, by where they are situated
perhaps?