One day when I came back to use the computer, which was switched on, I
kept pressing the keyboard but nothing came onto the monitor. I
switched off the power and switched on again, the screen came out for
a while, and went off again. So I decided to unplug the power plug of
the monitor and plug it back, and somehow the problem was solved. But
now, the problem came back, and now unplugging and plugging the
monitor power can no longer solve the problem... Is my monitor spoilt,
or does the problem lie somewhere else?

Please help! Thanks.

trunterzx wrote:
You don't say whether your monitor is an LCD, but I'll assume it is.

The monitor has a backlight inside it. The LCD panel controls
the transmission of light, and there is a light source behind
the panel.

The majority of LCD monitors have one or more CCFL (cold cathode
fluorescent) lamps for backlights. They need 700 to 1000V AC to
operate. A small rectangular circuit board has an "inverter",
which converts a low voltage like the 12V DC inside the monitor,
to the required high voltage AC to run the lamp. The AC is
also at a high frequency, so there won't be any flickering.

If the monitor lights up for a second or two, and then goes
dark, that is the inverter shutting off. It means the
inverter thinks it is overloaded, and so it has shut off.
This can mean a failure of the inverter, or an actual
short somewhere in the wiring (like dust or dirt forming
a conductive path for the high voltage to flow). Sometimes
the connectors on the inverter are corroded and make an
unreliable connection.

One test you could have tried, if you could still see the
monitor screen, is turn down the intensity setting of the
monitor. If you can do that, frequently the inverter will stay
running for a while longer. But it won't last forever.

This is really a shame for LCD monitors, because
everyone worries about the CCFL (the lamp itself)
and its 25000-35000 hour lifespan. But what seems
to happen instead, is problems with the inverter
mean never getting to see the lamp wear out.

Inverters can be replaced - the hard part is finding
an exact substitute. There are companies on the
web that sell substitutes, but you never know how
close they are to functioning like the original.
I doubt any company sells the exact same module
as the one inside your LCD monitor right now.
If only the LCD monitor companies sold replacement
parts, or were required to by law.

Paul

On May 9, 5:43 pm, Paul <nos...@needed.com> wrote:
Paul, thanks for taking the time to give all this very interesting
info on monitors. It's nice to know what's really happening "in
there". :-)
ATB
sandy58

"Paul" wrote:
Thanks for the info. Sorry I forgot to say more about my monitor. It’s
a BENQ monitor, and the model is Q7T4.

http://imagenes.solostocks.com/media...ia_1418683.jpg

So if the inverter is spoilt, does that mean I have to go and get a
new monitor? One thing I forgot to mention is that the green lamp
which indicates that there is signal from the computer remains on all
the while even when the monitor does not show anything. And the
monitor takes a longer time to go off when I leave the computer
switched off for a long time. Could it be a problem of the graphics
card? I’m using GeForce 8600.

--
Posted at author's request, using moderated http://www.HardwareForumz.com interface
Thread archive: http://www.HardwareForumz.com/Monito...pict90857.html

trunterzx wrote:

For an inverter problem, there are a couple possible symptoms. There
may be no light ever, coming out of the screen (complete failure).
There can be light for 2 seconds, followed by darkness. That is the
inverter shutting down on an overload. That means the inverter is
"weak", and can no longer support the load the CCFL lamp is presenting.

The LCD screen works on light transmission. If you could, somehow,
shine a light through the back of the screen, you'd see that the
screen was still working. It is just the light source that has
died.

There are web sites that sell replacement inverters, but I don't know
what the odds are that you'll successfully repair the monitor.
For a consumer, the easiest solution is to buy a new monitor.
It all depends on how much time you want to spend on it.

You'll notice here, that the people running this site, are making
a hefty profit. Which doesn't help matters either.

http://www.lcdpart.com/doc/inverter.html

An inverter can drive more than one lamp. Some of these little boards
drive a number of lamps. And in some of the larger display devices,
there can be multiple of these little boards. Obviously, at the LCD
monitor factory, they're not paying $69.99 for each inverter, or
monitors would be ungodly expensive. If the monitor cost $300, it
hardly makes sense to spend $100 on a repair that might not work.
If the monitor is really expensive, or a high quality one, then by
all means, try to repair it. If the monitor cost $1000, then $100
gamble is worth it. But at the $300 level, it'll be a decision
based on your own skill level at disassembling and repairing things.

(Example of an inverter)
http://www.lcdpart.com/Products/lg1501.html

Examples of installation procedures. Downloadable PDF shows how many
screws and whether things need to be pried apart or not.

http://www.lcdpart.com/doc/inverter_installation.html

There are way more monitor brands and models, than there are
suppliers selling replacement inverters. So you may not even find a
match for your model. Which makes the decision to buy a new
monitor, an easy one.

Paul