>I have a very strange problem with my Powerbook 540 b/w LCD Display: When I >start up my Powerbook everything works fine. But after some minutes it >starts to get more and more black at the borders. So when it's running for >maybe more than 2 hours i have very ugly dark spots (about 1/2 inch or even >more) at the edges. To get a blank screen again I have to shut power-down >the notebook for at least half a day or more. > >Thanks, >Kai
>This problem is seen in several different types of black and white >active matrix LCD screens, particularly the Duos. At this time, no >one seems to know what causes it, although it does not appear to be a >backlight problem. >Hmmm.... you think its the backlight getting old ? I remember I >tried seeing if the backlight was the problem with my DUo 280, and >the light came on at full strength.... but if you are saying it takes >a bit to see. I will do a backlight swap and see if this works. >thanks, >Mad Dog I think what happens is this: As the backlight ages, its resistance goes up. Most backlight power supplies are designed to maintain roughly constant current through the tube, and this helps prevent the light output from dropping dramatically right away. However, the voltage dropped across the tube does goes up, so the power dissipated by the backlight also goes up, making it run hotter. LCD gook is very temperature sensitive, and will go dark when hot. That explains why only the edge(s) go dark -- they're closest to the actual tubes, and also explains why waiting some time lets it work for awhile. I suspect that blowing cool air over the right parts of the display would allow the PB to run longer before the dark edges appeared. Of course, I haven't actually tested this theory to any real degree. But as a proud member of the "often wrong, but never in doubt" club, I don't let that stop me. :-) --Tom -- Prof. Thomas H. Lee Center for Integrated Systems, CIS-205 420 Via Palou Mall Stanford University Stanford, CA 94305-4070 http://www-smirc.stanford.edu 650-725-3709 ph, -3383 fax -------------------------------------------------------------------- mail2web - Check your email from the web at http://mail2web.com/ . -- PowerBooks is sponsored by <http://lowendmac.com/> and... Small Dog Electronics http://www.smalldog.com | Enter To Win A | -- Canon PowerShot Digital Cameras start at $299 | Free iBook! | Support Low End Mac <http://lowendmac.com/lists/support.html> PowerBooks list info: <http://lowendmac.com/lists/powerbooks.shtml> --> AOL users, remove "mailto:"; Send list messages to: <mailto:[EMAIL PROTECTED]> To unsubscribe, email: <mailto:[EMAIL PROTECTED]> For digest mode, email: <mailto:[EMAIL PROTECTED]> Subscription questions: <mailto:[EMAIL PROTECTED]> Archive: <http://www.mail-archive.com/powerbooks%40mail.maclaunch.com/> Using a Mac? Free email & more at Applelinks! http://www.applelinks.com
