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Dell Latitude Screen

01/19/2010 12:53 PM

Hi. I have been given a Dell Latitude to have a look at by a friend, because the backlight for the screen doesn't work. I am not sure whether this is due to the inverter or the backlight not working, and I don't have any way to test them. The laptop will turn on, and if a VGA cable is plugged in, it will output to a monitor just fine. Is there any way to test if the backlight works? I was reading you could input 12v to it, to see. I have had the inverter out, and there is no physical damage to it. I have found a used inverter on ebaY for £10, but don't want to make them pay that if the inverter is actually fine. Is there any way to test it?

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#1

Re: Dell Latitude Screen

01/19/2010 1:17 PM

Look here:

http://cr4.globalspec.com/thread/49060#comment510211

There are some ideas here, esp. Post #12

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#2
In reply to #1

Re: Dell Latitude Screen

01/19/2010 1:40 PM

i recently purchased a dell inspiron and had the same issue. after doing some research i determined that my black screen had nothing to do with the backlight or the lcd. I determined this by shining a flashlight on the screen while it was powered on to see if i could make out any images. i thn read a blog post by someone who had a problem with the switch that turns off the monitor with the screen is closed. i downloaded the service manual from the dell web site, and took the laptop apart so i could get to this button (mine is just a plastic cover on the top of the keyboard that gets pulled off) then i found the button under this cover was stuck in the down position, i grabbed it with a pair of tweezers and pulled it up. everything has worked fine since then.

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#3
In reply to #1

Re: Dell Latitude Screen

01/19/2010 2:07 PM

Yeah, if I shine a light on the screen, I can see the images of the desktop etc.

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#4

Re: Dell Latitude Screen

01/19/2010 4:54 PM

Check the drive transistors for source-drain shorts and check the output transformers for open windings or shorts.

The next step is to identify the power input and control pins on the inverter connectors. See what those are doing with the inverter installed and the computer turned on.

Note that a good inverter will shut down if one of the tubes fails to light off properly. In such a case, if you have an oscilloscope, you will see a few cycles on the output transistor gate drive, then a flat line. If that happens, the next step is to open up the display to check the tubes. If you can see the tubes and still have the ability to turn on power to the system, you can immediately detect a bad tube (pink tint, dim, or black). Caution: be careful not to take apart too much of the display. Almost all displays let you slide the tubes out of the side by removing one or two screws and sliding them out the side with the wires attached.

It is possible to detect a bad tube by inspection, although you have a higher probability of a false positive. If an end of any of the tubes is blackened over a length greater than 3 mm, this is probably the culprit. If I determine that I have a failed tube, I replace all of the tubes. I've seen too many forums where people whined about changing one tube, then having the display black out again in a few weeks. It's a lot of work to get into most of these displays, and you don't want to do it a second time too soon.

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#5

Re: Dell Latitude Screen

01/20/2010 2:52 PM

This is not a 100% test, but usually if its the flex connector, the screen will occasional function for a short time....If its the inverted, it will never do that.

Eexcept for when the inverter is overheating, it runs when cold and stops when warm......cleaning the inside of the laptop and fan may be needed....

Using laptops in bed/on a soft pillow or similar (like my daughter!) is bad as it usually blocks airways......it overheats and damages things...

By the way, the latitude of about 6 years ago was the worst laptop I have ever had, total crap and fully of cheap low performance chips.....my 2 cents worth...

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#6
In reply to #5

Re: Dell Latitude Screen

01/20/2010 3:32 PM

I know, it is crap. My friends inherited it. It has a P3 CPU!

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