Intermittent display


A

Andrew Eng

Hi, recently i encountered this problem on my PC. When i press the ON button, the monitor shows the normal starting up image for only 1 second and then it went black. Then, because my computer has a CPU FAN error (probably because the starting speed of my fan is a little slow), it would beep 3times and prompt me to press F1. During this time, the image would appear on the monitor for 1sec and then, becomes black again. Then, as it loads and enters window, it will flash yet again and i can see the cursor of my mouse at the center of the screen for that 1 second.

Everything is running normally as i can hear the start-up sound, and when i press [Window] + + , which is to shut down the comp, i hear the shut-down sound and the comp turns off. Throughout all this time, the monitor's power light is green and not orange. Which i think means that it is receiving signals from the computer.

I took out my graphic card and tested it on my friend's comp and it works. Then i took out all the connection to my hard-disk dvd-rom drive but the screen still flashes only once during start-up. Then i tried changing the ram to different ram slots but that also did not solve the problem.

So i suspect that either the monitor or motherboard is faulty. What might be the problem? Because the repair shop is very far and i don't wish to bring my cpu there only to find out that nothing is wrong with my cpu =x.


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P

Paul

Andrew said:
Hi, recently i encountered this problem on my PC. When i press the ON button,
the monitor shows the normal starting up image for only 1 second and then it went
black. Then, because my computer has a CPU FAN error (probably because the starting
speed of my fan is a little slow), it would beep 3times and prompt me to press F1.
During this time, the image would appear on the monitor for 1sec and then, becomes
black again. Then, as it loads and enters window, it will flash yet again and i can
see the cursor of my mouse at the center of the screen for that 1 second.

Everything is running normally as i can hear the start-up sound, and when i press
[Window] + + , which is to shut down the comp, i hear the shut-down sound and
the comp turns off. Throughout all this time, the monitor's power light is green
and not orange. Which i think means that it is receiving signals from the computer.

I took out my graphic card and tested it on my friend's comp and it works. Then i
took out all the connection to my hard-disk dvd-rom drive but the screen still
flashes only once during start-up. Then i tried changing the ram to different ram
slots but that also did not solve the problem.

So i suspect that either the monitor or motherboard is faulty. What might be the
problem? Because the repair shop is very far and i don't wish to bring my cpu there
only to find out that nothing is wrong with my cpu.


I would suspect the monitor. Take the monitor to your friend's place,
and connect it to his video card. It should go on for one second,
and then go black again.

If you unplug the VGA connector, from the computer, then plug it back in,
it should light up again for the 1 second period. So if you need to see
the screen at any instant in time, unplug and then plug in again. (I've done
this hundreds of times with my current LCD monitor, and it has lasted
more than five years so far.)

The monitor is lit by a CCFL backlight and inverter system. The
inverter converts low voltage into 700-1000VAC (about 3 watts of power)
at a relatively high frequency, to run the CCFL (cold cathode fluorescent
lamp). Depending on the size of the monitor, there can be multiple lamps
and inverter modules. Some inverter modules run multiple lamps.

The inverter has two operating states. The initial "ignite"
state, is at a higher voltage. Once the CCFL warms up a bit,
the voltage developed across the tube starts to drop. If
the inverter detects an overload, or the voltage drops
below the "holding" voltage, the CCFL goes off. And that
matches your symptoms.

An aging lamp might be noted by a discoloration of the light
coming from the lamp. While an inverter problem, may show as
a couple seconds of operation, followed by the light going off.

In some cases, changing the intensity setting of the lamp, may
allow it to operate normally for a couple weeks, before it
gives up for good. That might have worked in the analog control
days, where the tube voltage was actually varied by the adjustment
knob. Now, the system uses PWM (pulse width modulation), so it is
less certain that fiddling with the light output level of the
lamp, will help.

The replacement inverter for some monitors, costs about $70. And
isn't really worth that much (a good profit to be made). The
Internet sellers, sell generic replacements, with no guarantee
they are even close to being the same module. So if you attempt
a repair, there is no way of knowing how long it will last
(sort of like the repairs on my car).

The CCFL lamp and inverter system, is a bit sensitive to the quality
of the electrical connections. When you take the thing apart,
all the bits and pieces are important. Some lamps will have metal foil
around certain parts, and all of that stuff has to go back the way
you found it. If a high voltage connector is making bad connections,
or there is enough dust and dirt to promote a leakage path, that
might affect operation too. If you know the operating environment
was very dirty, perhaps a careful cleaning would help. But otherwise,
look forward to replacing something inside the monitor.

Good luck,
Paul
 
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A

Andrew Eng

I unplugged the VGA connector, plug it back in and it is exactly like what you said! The screen lights up for the 1 second period. I toyed with it for awhile and managed to get the screen to work. Then i changed some settings and hope it can last while i get a new monitor. A million thanks to you!! Saved me from the time and trouble of going to the repair shop!! Thanks again!!! ^^



Paul wrote:

Andrew Eng wrote:I would suspect the monitor.
10-Apr-10

Andrew Eng wrote:

I would suspect the monitor. Take the monitor to your friend's place,
and connect it to his video card. It should go on for one second,
and then go black again.

If you unplug the VGA connector, from the computer, then plug it back in,
it should light up again for the 1 second period. So if you need to see
the screen at any instant in time, unplug and then plug in again. (I have done
this hundreds of times with my current LCD monitor, and it has lasted
more than five years so far.)

The monitor is lit by a CCFL backlight and inverter system. The
inverter converts low voltage into 700-1000VAC (about 3 watts of power)
at a relatively high frequency, to run the CCFL (cold cathode fluorescent
lamp). Depending on the size of the monitor, there can be multiple lamps
and inverter modules. Some inverter modules run multiple lamps.

The inverter has two operating states. The initial "ignite"
state, is at a higher voltage. Once the CCFL warms up a bit,
the voltage developed across the tube starts to drop. If
the inverter detects an overload, or the voltage drops
below the "holding" voltage, the CCFL goes off. And that
matches your symptoms.

An aging lamp might be noted by a discoloration of the light
coming from the lamp. While an inverter problem, may show as
a couple seconds of operation, followed by the light going off.

In some cases, changing the intensity setting of the lamp, may
allow it to operate normally for a couple weeks, before it
gives up for good. That might have worked in the analog control
days, where the tube voltage was actually varied by the adjustment
knob. Now, the system uses PWM (pulse width modulation), so it is
less certain that fiddling with the light output level of the
lamp, will help.

The replacement inverter for some monitors, costs about $70. And
is not really worth that much (a good profit to be made). The
Internet sellers, sell generic replacements, with no guarantee
they are even close to being the same module. So if you attempt
a repair, there is no way of knowing how long it will last
(sort of like the repairs on my car).

The CCFL lamp and inverter system, is a bit sensitive to the quality
of the electrical connections. When you take the thing apart,
all the bits and pieces are important. Some lamps will have metal foil
around certain parts, and all of that stuff has to go back the way
you found it. If a high voltage connector is making bad connections,
or there is enough dust and dirt to promote a leakage path, that
might affect operation too. If you know the operating environment
was very dirty, perhaps a careful cleaning would help. But otherwise,
look forward to replacing something inside the monitor.

Good luck,
Paul

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