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monitor problem

 
 
Jr.
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      09-06-2007
My lcd flat-screen monitor is beginning to "flicker".
I see "wavy" lines especially in the blue portions of the screen.
Is it dying?



 
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Paul
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      09-06-2007
Jr. wrote:
> My lcd flat-screen monitor is beginning to "flicker".
> I see "wavy" lines especially in the blue portions of the screen.
> Is it dying?
>


Do the symptoms change, if you adjust the light output of
the screen ?

The backlight operates at two frequencies. At a relatively
high frequency (> 25KHz where it is inaudible), the inverter
converts 12 volts DC to 700 to 1000 Volts AC, to make the
compact fluorescent backlight tube light up.

There are two methods to control the intensity of the screen.
A simple, limited range of voltage control is possible, and
that is an analog method of some sort. (That might be used on
an older monitor.)

The second method, is low frequency duty cycle modulation.
The 25KHz behavior is turned on and off at a much lower frequency,
like 100+ Hz. The duty cycle of the modulation is varied,
and by doing this, a wider range of CCFL light output is
possible.

In terms of the scanning of the screen, the signals present
on VGA are R,G,B and H,V. RGB are the three colors, and they
are carried on coaxial wires (signal wire with foil ground
around the wire, for shielding and controlling the desired
75 ohm impedance). The RGB signals are virtually useless,
without synchronization signals. H and V are horizontal and
vertical sync, and the display of the RGB signal is
coordinated by the sync signals. The edge of a changing
voltage level on a sync signal, controls where the RGB is
aligned to the left edge of the screen. Similarly, the vertical
scanning (placement of line 1 at the top of the screen), is
controlled by the second sync signal. If there is any problem
with synchronization, the symptoms can vary.

Many people have seen a TV set "scroll" or wave, when sync
is lost. The old vacuum tube sets, used to have knobs that
the users would adjust, to stop the scrolling.

The LCD monitor though, is different. If there is a signal
problem coming from the video card, certain kinds of failures
can be recognized by the hardware monitoring done inside the
monitor. For example, the monitor does frequency checks on
H and V, to determine whether the scan rate being used is
within the capabilities of the monitor. If they are not, the
OSD (on screen display) will appear and give a warning message.
During that time, to make the OSD image on the screen, the
monitor will substitute its own control signals, in order
to make a nice image on the screen.

Now, if there is a signal level or quality issue with H and V,
not all possible failure modes may be detected. On the one hand,
an inconsistently received H or V, might trigger the frequency
check of the OSD, or it might simply give a crappy picture.

So when you say "wavy", that sounds to me like a sync problem.
Either a bad cable is affecting H or V, or a bad video card
output is affecting H or V. Remove the cable and inspect the pins
on both ends, for problems.

I've described both how the light is made, and how the screen can
be wavy, to get you to comment on whether the problem seems to be
related to light intensity, or the problem is related to the
painting of the image on the screen. From a percentage point of
view, most problems with LCD monitors seem to be with the lighting
(failed inverter or backlight is becoming dim). There are relatively
few comments about sync loss.

Using DVI should give a different set of failure modes, but I'd
have to look up the encoding method, to suggest ways it could
fail.

Paul
 
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Jr.
Guest
Posts: n/a
 
      09-07-2007
So, how do I figure out if it is the monitor or the video card?

"Paul" <(E-Mail Removed)> wrote in message news:fbpa5v$ev7$(E-Mail Removed)...
> Jr. wrote:
>> My lcd flat-screen monitor is beginning to "flicker".
>> I see "wavy" lines especially in the blue portions of the screen.
>> Is it dying?
>>

>
> Do the symptoms change, if you adjust the light output of
> the screen ?
>
> The backlight operates at two frequencies. At a relatively
> high frequency (> 25KHz where it is inaudible), the inverter
> converts 12 volts DC to 700 to 1000 Volts AC, to make the
> compact fluorescent backlight tube light up.
>
> There are two methods to control the intensity of the screen.
> A simple, limited range of voltage control is possible, and
> that is an analog method of some sort. (That might be used on
> an older monitor.)
>
> The second method, is low frequency duty cycle modulation.
> The 25KHz behavior is turned on and off at a much lower frequency,
> like 100+ Hz. The duty cycle of the modulation is varied,
> and by doing this, a wider range of CCFL light output is
> possible.
>
> In terms of the scanning of the screen, the signals present
> on VGA are R,G,B and H,V. RGB are the three colors, and they
> are carried on coaxial wires (signal wire with foil ground
> around the wire, for shielding and controlling the desired
> 75 ohm impedance). The RGB signals are virtually useless,
> without synchronization signals. H and V are horizontal and
> vertical sync, and the display of the RGB signal is
> coordinated by the sync signals. The edge of a changing
> voltage level on a sync signal, controls where the RGB is
> aligned to the left edge of the screen. Similarly, the vertical
> scanning (placement of line 1 at the top of the screen), is
> controlled by the second sync signal. If there is any problem
> with synchronization, the symptoms can vary.
>
> Many people have seen a TV set "scroll" or wave, when sync
> is lost. The old vacuum tube sets, used to have knobs that
> the users would adjust, to stop the scrolling.
>
> The LCD monitor though, is different. If there is a signal
> problem coming from the video card, certain kinds of failures
> can be recognized by the hardware monitoring done inside the
> monitor. For example, the monitor does frequency checks on
> H and V, to determine whether the scan rate being used is
> within the capabilities of the monitor. If they are not, the
> OSD (on screen display) will appear and give a warning message.
> During that time, to make the OSD image on the screen, the
> monitor will substitute its own control signals, in order
> to make a nice image on the screen.
>
> Now, if there is a signal level or quality issue with H and V,
> not all possible failure modes may be detected. On the one hand,
> an inconsistently received H or V, might trigger the frequency
> check of the OSD, or it might simply give a crappy picture.
>
> So when you say "wavy", that sounds to me like a sync problem.
> Either a bad cable is affecting H or V, or a bad video card
> output is affecting H or V. Remove the cable and inspect the pins
> on both ends, for problems.
>
> I've described both how the light is made, and how the screen can
> be wavy, to get you to comment on whether the problem seems to be
> related to light intensity, or the problem is related to the
> painting of the image on the screen. From a percentage point of
> view, most problems with LCD monitors seem to be with the lighting
> (failed inverter or backlight is becoming dim). There are relatively
> few comments about sync loss.
>
> Using DVI should give a different set of failure modes, but I'd
> have to look up the encoding method, to suggest ways it could
> fail.
>
> Paul



 
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Paul
Guest
Posts: n/a
 
      09-07-2007
Jr. wrote:
> So, how do I figure out if it is the monitor or the video card?
>


Try the monitor on another computer and see if the problem is
still there.

Try a different monitor with the problem computer, and see if the
same thing happens.

If you have one, try a different video card cable, as sometimes
the problem is with the pins on the connector.

Without test equipment, the easiest way to test, is to swap stuff
and try again.

Paul

 
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