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Gateway PA2 LCD backlight refuses to light up - even after new inverter and new LCD

Posted on 2008-09-29
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Last Modified: 2013-11-17
Well,

I've replaced a lot of inverters in my day.  This Gateway laptop was displaying a very dim screen, so I reflexively ordered and installed an inverter.  The new inverter didn't fix the problem.

Instead of messing with the CCFL replacement, I decided to order a brand-new LCD.  I installed it just now, and it has the same dimness problem.  

Sometimes there is a switch that the laptop's lid depresses when it is closed.  Once, I almost replaced the inverter, but I saw a piece of junk sticking the switch down.  When I removed the junk, the backlight blinked on immediately.  

I cannot find any switch like this on the Gateway.  The keyboard bezel is smooth - no holes.  Now what?  What else could it be?  I did not replace the video cable yet, but it is in good shape and no matter how much I wiggle it, I can't even get a blink from the backlight.  With a bad cable, the problem should be intermittent.  

Anyway,  what do you think?  Is there some sort of magnet that could have fallen out of the way?  

Jason
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Question by:compexvi
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rindi earned 500 total points
ID: 22603679
Sometimes if there are such switches they are using a reed switch (a magnetic switch which is flipped if a magnet comes close). If you have such a switch then you wouldn't see any moving parts. Anyway, those switches hardly ever break, but of course it is possible that the magnet itself has fallen off the display. But since you can see a picture I don't think there is a problem with a lid switch, it would turn off the display completely. Maybe you have a problem with the power supply or cable for the inverter.
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by:compexvi
ID: 22605288
Thanks for the comment.  

I took apart the bottom case and found a couple of things.  The laptop has a separate video card, so I could actually replace that.  Also, the magnet in the top case seems to be in the correct spot.  

To be sure I am not missing something, do you know of any place in Windows where you can turn off a backlight?  It's a long shot, but maybe a software switch got toggled somehow.  I have played with the brightness and it is set to 100%.  

If not, I suppose it comes down to the question - should I replace the cable or the video card?  

Thanks again.
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by:rindi
ID: 22605649
You may be able to change the brightness using software, but that will be typically done using 3rd party tools from the PC manufacturer (or by using the function keys). You can always check the hardware functions by booting the PC using a LiveCD like puppy or knoppix.

http://www.puppylinux.org/
http://knoppix.net
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Author Comment

by:compexvi
ID: 22605901
Brilliant idea on the bootable disks.  The backlight is still off, though.  Since the computer reports that the brightness is at 100% when I try to make it brighter in Windows, I am guessing the 3rd party tool that is installed is not doing anything to hamper the backlight.  

I just ordered the LCD cable, Express Mail.  I hope it will fix things.  If you have any other inspiration in the mean time, I am all ears.  

Thanks,

Jason
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Expert Comment

by:rindi
ID: 22605933
It could also be the power that supplies the inverter, but I wouldn't know how you could test or repair that.
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Author Comment

by:compexvi
ID: 22638050
So, I got the cable in and the computer still has the same problem :/
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Author Comment

by:compexvi
ID: 22690050
I just told my client that he needs a new motherboard.  Thanks for the help, rindi.  I'll give you the points because you took me in a couple of directions I wouldn't have considered.

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