No display on notebook screen, but external monitor works

Hello all,

Friend of mine gave me his Acer Aspire 7720z notebook to see if I can do anything to bring display back.
There is no display on notebook's screen - just black screen. Not even faint/dim image at all. On external monitor everything works fine.

Now, here is what I have tried but nothing helped:
- checked all combinations when displaying on two monitors, black screen on notebook remains with or without external monitor plugged
- reinstalled video driver
- reinstalled whole Windows OS
- upgraded to newer BIOS version
- disassembled notebook to check if all wires are properly connected (twice)
- bought new screen inverter, replaced it - still nothing

Notebook has Intel(R) 965 GPU. Gpu chip on motherboard looks normally, without any signs of melting or overheating. Notebook is not overheating at all, temperature sensors give reasonable values.

I think it is screen backlight problem, but I would really like to be sure before starting adventure of replacing LCD's CCFL backlight lamp.

Although screen remains black all the time, I can see something like flicker when starting windows or when changing screen resolution, but I really have to pay close attention to see that flicker, sometimes I think I am just imagining it.

Any ideas? Suggestions? What else could I try, or should I proceed with replacing CCFL backlight lamp?
Appreciate any kind of help..

 

It can't be an integrated chip failure since it works fine with an external monitor.

That leaves the LCD screen, an inverter, cable or LCD back-light. Not what you have replaced an inverter we can ignore this one.

If it was to be a CCFL failure you could still see the LCD itself working if you had a direct light source aimed at the screen.
It definitely is visible- if you have another notebook you can check how it looks with Fn+F6 (on Acers) which switch off back-light.

So if you can see something on the screen this way- it's CCFL but if you can't it isn't. That would only leave LCD failure or LCD cable failure.
Replacing the cable is much cheaper so that would be the thing to go for.

 

Thanks for reply,

Before looking for new cable or LCD screen, there is one thing I would like to check. I would like to check if lid-close switch is not making this problem, but don't know where it is located. Or if it is some magnet how could I check if it properly works. I have set Windows to go to sleep mode when closing the lid and it works (on external monitor of course), but wonder if maybe this switch is anyhow disabling power source to notebook screen, or inverter (or something similar).