Gvnaena said:
Thanks for all the guidelines.
The LCDs are of different brands. Their death are some what similar.
Throughout their life time, I have not abuse them in any obvious way.
They were just sitting on my desk. As for the environment, it is a
small apartment, fairly clean (according to my standard). I do have a
rabbit, who generates quite a lot hair and lint. I do have a negative
ionizer, but I think it is innocent since its purchase was long before
these problems.
As for the LCDs:
1) View Sonic 17" LCD (I forgot the exact model) with DVI input. One
day it decides to turn itself off while I was typing something (it looks
as if it was turned off manually). That time I was able to turn it back
on. And such condition happens a few time after that, and one day it
turns itself off again, and this time when I try to turn it on, the
power LED just keep flashing, and nothing comes up (the back-lamp,
if that is what it's called, does not turn on neither).
2) Dell 17" LCD, VGA input. One day just turn black. When I try to
turn it off and on again, the back-lamp works, but no picture.
3) X2gen 17" LCD, VGA input, with speaker. I have been using this baby
for a year or so in my office, and it works just fine. 2 month since it
comes to my apartment, the picture start jump from time to time. As
time goes by, this happens more and more often. Some times the "menu"
stop working, and now the "phase" is also messed up (no matter how I
set the phase option, there will be a blurry vertical strip). Some
times it will also turn itself off. Unplug and replug the power helps.
But I know it is going to die soon.
All LCDs are plug into a surge protector, which is also where the
computer and speakers plugged into. I have a NVidia GeForce 6200 LE card.
Sometimes the card reaches 71 degree Cel. But the problems started
back in winter when the card was usually only 62 degree Cel.
I don't know if the power is clean or not, but lightning storms
do not come and visit often.
In the first case, it sounds like the power supply of the monitor, detected
a problem. Either the Viewsonic overloaded its switching power supply, or
the switching power supply switched off after receiving a power transient.
The backlight cannot come on in that case, because there is no longer
any 12VDC available inside the monitor.
The second failure is more interesting, because the backlight is still working.
The backlight runs at about 1000VAC, and is powered by an inverter. The
backlight draws a low current, like 3 milliamps, for a total power draw
of 3 watts per cold cathode fluorescent lamp. The inverter is a long
rectangular module near the backlight, that converts 12VDC to 1000VAC.
Since the backlight was still running, we know that 12VDC was still available,
and the failure was probably not due to dust entering the display. It is
always possible for a contaminant to enter where there is high voltage,
and for some arcing to appear. But the backlight on this monitor is still
working.
In the third case, I was going to suggest a power issue, but you mention
that unplugging and replugging helps. If a monitor uses an external 12V
supply as the power source, there is still a conversion process inside the
monitor, to convert the 12V to the lower voltages that the logic ICs need.
Maybe the jumping is caused by a problem with that lower voltage conversion.
The symptoms are all different, and don't point to one specific cause.
About the only voodoo I can suggest, is to install a UPS before the computer
and monitor. There are various kinds, and the cheapest UPSes don't do much
for power conditioning. The "line interactive" with voltage regulation is
a possible solution, to improve power quality. The "double conversion" type
would be the cleanest, but would also be more expensive. This document
explains the types (but I'd have preferred more detail in their diagrams).
http://www.apcmedia.com/salestools/SADE-5TNM3Y_R5_EN.pdf
I wish there was a cheap way to monitor AC power quality, but I haven't heard
of one. I use a multimeter to check the average voltage value on my AC
(because the power company has recently been making changes to the
distribution in the neighbourhood, and the voltage has varied from
104VAC to 120VAC). But if something is going to kill the monitor, it
would be a transient that would do it, and a multimeter cannot detect
that (the reading rate is too slow).
The kinds of failures I'm familiar with, as seen on postings to USENET,
are backlight/inverter failures. In that case the monitor is still working,
but there is no light source so you can see the screen. The other kind of
failure, is bright lines on the screen, where the mechanism used to drive
pixels on the screen fails. In monitors where this was a chronic problem
(bad batch of monitors), failures of this type might occur after only
three weeks of usage.
Since your failures don't fall into these catagories, I have to look at
the stressors of a monitor. The AC power input is one point where the
monitor can be abused (but the switching conversion processes being used,
should filter at least some of that). The VGA or DVI connector is another
stress point. Since the ground shell on the connector makes contact first,
the signal ground should be well established. Which makes it harder to apply
an illegal voltage value to the pins, unless the video card has had a weird
failure. And pressing on the screen (causing a physical failure) would
be another way to stress the monitor. Excessive heat or corrosive gas
atmosphere might also lead to premature failure, but there is nothing
in your description to suggest that.
Finally, if the third LCD dies on you, you could consider switching to
a CRT. At least when it dies, the symptoms will be different
(Some CRTs...)
http://www.nm-select.com/searchresults.asp?search_id=1
Paul
