LDC Screen flickers
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From: French Quarter on 19 Feb 2010 01:47 XP Home. The LCD Screen flickers. You have an idea of some parts I can change to fix it? What would you do? Thank you for your time. Compaq Nx6125 AMD Turion 2Ghz Thank you ~ Enjoy The Rest Of Your Cajun Crawfish
From: Paul on 19 Feb 2010 02:39 French Quarter wrote: > XP Home. > > The LCD Screen flickers. You have an idea of some parts I can change to > fix it? > What would you do? > Thank you for your time. > > Compaq Nx6125 AMD Turion 2Ghz > > Thank you ~ Enjoy The Rest Of Your Cajun Crawfish There are two kinds of flickering. 1) Irregular flickering. That could be a bad contact in the wiring of the backlight and inverter. Or, the inverter could have a problem. Or the high voltage could be leaking or arcing over. Or one of the connectors could be loose in the panel. The inverter outputs 600V to 1000V, at a frequency of 25KHz or so. Total power is about 3 watts per CCFL backlight tube. So when I refer to high voltage, it is that voltage coming from the inverter and feeding the backlight that I'm referring to. The white light behind a lot of LCD monitors, comes from cold cathode fluorescent lamps. Only a few monitors use LEDs for the light source. In addition to running at 25KHz, to make the high voltage, the inverter can also be pulse width modulated at a frequency in the 100+ Hertz range. The purpose of that, is to implement brightness control. By varying the percentage of time the backlight is powered, it allows the backlight to be brighter or dimmer, without affecting the color balance of the tube. If they just changed the voltage on the tube, the color would be "brownish" at low voltage. The color would be thrown off. That kind of PWM control of brightness, is not supposed to be visible to the user. So maybe if that was a bit wacky, that could account for some flicker. It could even be a video driver issue, as sometimes the video card can be convinced to do crazy things by the software. Test the monitor on a second computer, to see if the video card makes it do the same thing or not. That will help you decide whether the feature is coming from the monitor, or the video card. If the refresh rate of the video card is set to 75Hz, try setting it to 60Hz, as for a lot of monitors, 60Hz is the normal rate that the frames are updated on the monitor. 2) Regular flickering. First of all, flicker on an LCD is different than flicker on a CRT. The sweep on an old CRT monitor, begins to decay almost immediately. The CRT phosphor has a limited persistence. To combat this, people use higher "refresh rates" on a CRT, such as 75Hz or 85Hz, which is starting to move above the frequency that people can still see the CRT flicker. An LCD is entirely different. The image on the screen, persists for the whole frame time. And this is why, when the human eye looks at an LCD screen at 60Hz, there normally isn't any flicker. So not as high a refresh rate is needed, for ordinary LCD monitors, because there isn't a phosphor that is decaying during a frame time. Because the image is present for the entire frame time, before it changes, there isn't the same flicker effect as a CRT. OK, so why do people see "regular flicker" on an LCD ? Some monitors contain an optimization, intended to improve the responsiveness of the LCD monitor. It involves blanking portions of the screen. This would be invisible to a lot of people, but some people seem to see this optimization and it irritates them. In some cases, this can be turned off in the OSD (On Screen Display used to control the monitor). The following article contains lots of information about tricks used in LCD monitors - it is worth reading the entire article when you have time. http://www.xbitlabs.com/articles/monitors/display/lcd-parameters_4.html So first, you have to decide what kind of flickering you're seeing. If the flicker is a regular and consistent effect, then look in the OSD for an item to disable. If the flicker is irregular, it might have something to do with the backlight. In some cases, it can be a video driver problem, in which case, testing the monitor on a second computer is recommended. Paul
From: Bob I on 19 Feb 2010 08:24 Flickers? LCD screens use a backlight. French Quarter wrote: > XP Home. > > The LCD Screen flickers. You have an idea of some parts I can change to > fix it? > What would you do? > Thank you for your time. > > Compaq Nx6125 AMD Turion 2Ghz > > Thank you ~ Enjoy The Rest Of Your Cajun Crawfish
From: French Quarter on 19 Feb 2010 10:05 Paul, I can never thank you enough for taking the time to post all that INFO. You are one sharp HARDWARE dude. Too bad you don't like Cochon De' Lait
From: French Quarter on 19 Feb 2010 10:06
Thank you Bob, I will change the back light first. |