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Thread ID: 50237	2004-10-14 20:40:00	FAQ #55 - Why has my screen gone funny colours?	-FAQ- (807)	Press F1

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281184	2004-10-14 20:40:00	FAQ #55 - Why has my screen gone funny colours? Originally written by Billy T Computer screens often show funny patterns or colours but most can be explained simply or fixed without too much trouble . The biggest thing is actually knowing what is going on . Here's Billy T's guide to screen effects that may or may not be a disaster in the making . 1) I see funny dark lines like water ripples and they move and change when the screen is brighter/darker This is known as Moire Effect and is a beat-pattern caused by optical interference between the scanning lines of the CRT and the dot pitch of the shadowmask . It typically shows as shimmery curved lines on screen, slightly darker than the background, and the lines will move and vary in intensity with brightness changes . 2) I've got coloured blotches all over my screen Multi-coloured blotches are Colour Purity Errors caused by external magnetic fields causing misregistration of the electron beams onto the colour phosphors of the screen . This can usually be cured by using the degaussing (demagnetising) function of the monitor but if severe, it may need manual degaussing with an external degauss wand (take it to your local TV shop but phone first as not all have degauss wands these days) . Alternatively, put a decent sized plug pack on an extension lead, switch on and rub it over the screen in a circular motion for a minute or so, moving it away slowly when you are finished and unplugging when about a metre away from the screen . You will know if it's working because you will get image distortion and rainbow effects on screen while rubbing . Billy's tip: don't rub the screen surface too hard, you may mark it . If you are too strong for your own good, wrap the plugpack in a hanky or paper towel . Purity errors are usually caused by static magnetic fields only, (speaker magnets, fridge magnets etc) but can occur if you turn your screen around and forget to degauss, because the earth's magnetic field will also upset it . For freedom from that effect, if you have to move your monitor frequently, line it up east-west and degauss, then it should swing around without problems . If it is still touchy, try setting it up in the midway orientation between the two positions you use most and degauss several times . Billy's tip: If you brought your screen in from overseas, it may be a Northern Hemisphere model and could need several degausses to get right, if it comes right at all . If in doubt, turn it upside down and degauss . If it looks OK upside down, that's the answer . Either take up yoga or buy a new screen . This effect gets worse the further south you travel . I kid you not, would Billy lie? Purity can also be upset if an appliance is turned off right alongside . Vacuum cleaners have been known to offend . 3) I see dirty patches or smudges when my screen is white or light coloured, like when I'm doing work processing "Dirty" patches or "smudges" are either mild purity errors or an effect called White Uniformity Error . They are caused by minor beam registration errors and commonly show up on very light screens if you have the brightness/contrast set too high . This heats the shadowmask and makes it bow outwards . It should go away at lower brightness levels . This effect is particularly common on very big screens (>17") and is a warranty matter if it appears at normal brightness and contrast levels . Check it on the blue or red screens at the monitor check site in 5) below . White uniformity is easiest to see as pink on blue or yellow on red . Green is hopeless . 4) My screen shakes and shimmers and I get moving dark lines . It seems to come and go at different times of the day Broad dark lines and images that that shimmer or shake are caused by external alternating electromagnetic fields from other electrical appliances, power wiring in walls etc . Plugpacks (power bricks) are particularly bad and put out a very strong field for about 25-30 cm around the brick . Try it, you won't hurt your screen . 5) My screen has a funny pink/blue/purple [your colour here] tint and it is making me feel green to look at it Screen tinting is usually either a slight excess of one primary colour or a slight lack of the other two primaries, but to explain that properly we need to talk about Additive Colour Mixing . Computer monitors and TVs emit coloured light which is additively mixed by the human eye to produce the full range of colours we see on screen . Red, green and blue are the three primary colours, and their complementary colours are magenta (red + blue), cyan (blue + green) and yellow (green + red) . Printing is subtractive, hence the use of cyan/magenta/yellow primaries in your inkjet . So, if your screen has a dominant colour, you can work out what is going on by the colour cast . A weak primary colour electron gun will produce a complementary colour cast, while an over-active primary gun will produce a primary colour cast . A primary colour cast is almost always caused by a fault inside the monitor though it can be a video card faultin some rare circumstances . A complementary colour cast can be any one of a plug & socket fault involving the video lead, loss of or weak primary in the monitor, or again a rare & unusual video card fault . The easiest way to eliminate the video card fault is to connect the monitor to another computer . Go here ( . monitorsdirect . com/toolkit/" target="_blank">www . monitorsdirect . com) for a free monitor colour check . Go to the Launch Calibrator button . It requires macromedia Flash, and unfortunately it only works in IE 5 or higher . In some tests I made in IE6, clicking on the Launch button produced a blank black screen . If that happens to you, use Alt-F4 to close that page and return to the start point . Note that some selections show a black screen for several seconds (depending on the speed of your computer and connection) before bringing up the info so be patient and only close if it is clearly not going to work . You select your test from a menu, and each test screen comes up with instructions . To see the test across the full screen you have you click the Go button at the lower RHS of the screen Yellow tinges in red or red tinges in blue indicate purity errors . Coloured fringing (primary or complementary) on bright objects is an indication of a tired electron gun . This is usually the red gun because that one works hardest . From memory a white screen is about 60% red, 30% green and 10% blue . Might be time for a new monitor . 6) Should I leave my monitor on all the time? You can if you want to, but screen life is counted in 1000's of hours and there are 8760 hours in a year . (8784 in a leap year) . Most screens have a useful life of 15-20,000 hours so how you use them up is your decision . Oh, and another thing, the bigger the screen, the shorter the life . I turn mine off when not using it . 7) My screen is going fuzzy & blurry, is it faulty or should I give up drinking? Fuzzy or blurrry images are usually a focus problem . This can be due to old age (you or the screen) or over indulgence . If you think it's the screen, wait until you can work in subdued light then set up a screen full of 18 to 24 point capital H's, turn off the monitor (NOT the computer) and wait a couple of minutes then turn back on . Watch the screen as it comes back up for colour tinting and focus . If it takes more than 15 seconds to show a good untinted B & W image it may be getting tired . See the colour section above to find out which gun is dying . The H's will be blurry at first but should be in sharp focus within 30 seconds . If they are not but the colour is ok, check the brightness and contrast settings (see below) and if they are already optimised you may need to adjust the focus . If the H's colour fringe and get even worse when you wind up the brightness/contrast it might be time to retire the old girl . One last tip: To set up brightness and contrast correctly, dim the lights and turn both to zero . Then advance the brightness until the screen is faintly lit . Now set the contrast to suit . That should be it, but a minor tweak of the brightness may be needed . Brightness is not actually brightness at all, it is really black level . If you find you need both up full for reasonable viewing then again, it may be time to think about a new monitor . This goes somewhere, but not sure where: I neglected to mention that many monitors offer a Moire effect adjustment that can reduce that problem . In my experience the improvement is limited but used in conjunction with brightness and contrast settings it can be useful in some cases . It may also help to change the refresh rate slightly, say from 72Hz to 75Hz, or 75Hz to 85Hz (or vice versa) . New On-Line Monitor Test Site thread ( . pcworld . co . nz/thread . jsp?forum=1&thread=51894&message=320599&q=monitor+test#320599" target="_blank">pressf1 . pcworld . co . nz) . Original FAQ available from here ( . pcworld . co . nz/thread . jsp?forum=1&thread=26660&message=96639&q=FAQ+%233#96639" target="_blank">pressf1 . pcworld . co . nz) .	-FAQ- (807)
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