laptop display (backlight /inverter)

Hi all

I have an acer aspire 5100 15.4inch laptop.Its display is very dim, I hardly see the image. screen is light black in color :)I have connected the laptop to the external monitor using VGA, its working fine.

I opened the lcd. I think the problem is with the inverter or the backlight.

1)How do i check if the problem is with the inverter or backlight?

Its easy job to change inverter. But replacing the backlight is very tough for me in shops they charge ?80 – ?90 where the back light costs around ?10. I cant afford.

any help will be appericiated