Laptop Screen is not detected, cant figure out why

rav007

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May 7, 2012
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Hi

Friday night of last week I was watching the classic 1989 Batman on my laptop and shut it down in the early hours of the morning. When I woke up on saturday morning and switched it on, the screen was not working although there was plenty of activity otherwise. I am currently in France, away from my home (UK) and so I have nothing with me and naturally I panicked. I finally got level headed and tried to diagnose the problem:

So there is no sign of life, shining a bright light on the screen there is nothing. I gained access to an external monitor on monday and figured out that the vga out works so I am able to use my laptop when I have a monitor around. Using this I have narrowed it down to the motherboard connection to my screen, the cable connector, the inverter/backlight or the lcd panel itself. I should mention the laptop is a Toshiba L500-128, a 2009 model L500 with the last of the core2 duo series, its getting on a bit but has been working like a champion nonetheless.

I have been having difficutly diagnosing further because I dont have spare parts to isolate the issue and before I fork out money which I dont have, I thought I would post on here. What I have done however, is found out that my LCD panel and inverter are connected to the motherboard via the same cable, which also connects my webcam. The cable can be found here: http://www.amazon.co.uk/eTrader-Direct-Original-Satellite-L500-11V/dp/B00AYEH2YE/ref=sr_1_1?ie=UTF8&qid=1366200795&sr=8-1&keywords=l500+lcd+cable

Now my reasoning was if the webcam still works then the cable should be fine and therefore the motherboard connection is also fine. I confirmed this just before writing this post, I unscrewed the screen bezel and whilst having my webcam application launched I unplugged the connector and plugged it back in to the webcam module and it is definitely supplying the webcam with life implying the cable works. Would you agree that the cable and motherboard can be diagnosed as working? This would leave just the panel and the inverter/backlight. Now here is my final piece of diagnosis: I have a system which dual boots ubuntu 12.1 and windows 8. Regardless of which OS I am in, they simply do not recognise that my laptop has a screen, they just see the external. I have done various driver reinstalls and so on but this is beyond a driver problem because the screen wont even show the boot screen! It only stands to reason that the problem is the inverter/backlight or the lcd panel, but I am leaning towards the inverter/backlight. I dont know enough about this kind of stuff, I have looked at forums and FAQs over the past few days to fill up with knowledge, but this is where I need help. I say inverter/backlight because it seems as though they .."control?"... the screen. So if they are gone, no screen would be detected? I could be entirely wrong so any ideas would be appreciated before I spend £150 trying to get it fixed and potentially failing

Thanks :)


 

ratedk

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Mar 31, 2011
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I'm pretty sure that the screen in your model is a CCFL backlight. Newer laptops use LED, and don't have an inverter.

The inverter & CCFL backlight are not associated with the actual picture on the screen (other than they are part of the small bundle of wires that are contained in the video cable - along with the built in camera). Even with a bad inverter or backlight, the screen would still show a picture, it would just not be lit. Shining a light on it would make it possible to see the screens image.

I would suspect that the screen itself is the issue. There will be a model number on the back of the screen that you'll want to match to get the proper replacement.
 

rav007

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May 7, 2012
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Ah, I see that now. So saying that is the case, I guess logically if the screen is at fault then the machine is not detecting a screen to display the image, but also I guess that if the machine doesnt detect the screen, the inverter and backlight would also "bypassed" seen as there is no screen to backlight... correct? If this is the case it makes perfect sense to me because the screen has nothing on it, nor is it backlit. I am just trying to isolate one component at the main culprit

On the topic of screen replacement, I can do this on my own for sure but the problem I have is the whole ccfl + inverter thing. The ccfl panels I find online for my model of laptop are in excess of £150, where if I look at LED monitors, they are around £40. My specific laptop only came with the ccfl, but the later models which are the exact same laptop but with newer components (intel socket g1, ddr3 ram, etc) have an LED monitor. cosmetically is looks identical to mine, and the motherboard connection socket is also the same, but the cable only has a socket for an LED panel at the bottom of the panel, and then a connection to the webcam implying no interver. Would it be safe for me to replace my entire unit from the motherboard cable to the inverter and ccfl, with a new LED cable and LED panel?
 

rav007

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May 7, 2012
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Ah, I see that now. So saying that is the case, I guess logically if the screen is at fault then the machine is not detecting a screen to display the image, but also I guess that if the machine doesnt detect the screen, the inverter and backlight would also "bypassed" seen as there is no screen to backlight... correct? If this is the case it makes perfect sense to me because the screen has nothing on it, nor is it backlit. I am just trying to isolate one component at the main culprit

On the topic of screen replacement, I can do this on my own for sure but the problem I have is the whole ccfl + inverter thing. The ccfl panels I find online for my model of laptop are in excess of £150, where if I look at LED monitors, they are around £40. My specific laptop only came with the ccfl, but the later models which are the exact same laptop but with newer components (intel socket g1, ddr3 ram, etc) have an LED monitor. cosmetically is looks identical to mine, and the motherboard connection socket is also the same, but the cable only has a socket for an LED panel at the bottom of the panel, and then a connection to the webcam implying no interver. Would it be safe for me to replace my entire unit from the motherboard cable to the inverter and ccfl, with a new LED cable and LED panel?
 

ratedk

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The backlight & inverter will function separately from the screen. They operate independently from each other.
If both the screen (picture), and backlight are out. You may want to try to replace the video cable first - it may be a cheaper solution. I didn't understand that they were both not working from your first post.

In regards to the expense of the screen, the older technology is not being produced in as much quantity as the newer stuff so the price goes up. I've seen some adapters that will allow you to use a newer LED screen with the older inverters. If you search ebay for your screens model number, some sellers will offer a new LED screen with the adapter as a cheaper solution.
 
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