Lenovo ThinkPad Edge E520 no backlight.

[siddiq]

Hi everyone, Lenovo ThinkPad Edge E520 [LGG-1 MB] has no backlight. All voltages and fuses are intact but, there are some voltage observations i made on the lcd connecter.

pin 1,2,3 - 20v [adaptor inserted]
pin 6 - 3.3v
pin 5 - 0.017v
Pin 7 - 0.015v
pin 16 - 3.29v
pin 18 - 1.812v [without screen connected voltage is 3.3v]
pin 19 - 0.015v
The LED screen is okay and i've tried different screens. I will also like to know the location of R4901. I will post pictures to make it easier. Any help will be appreciated.

[jelonek]

Hi, i would check the lcd cable first?

[jack155]

check 3v PIN 27 BLON U2701A (NPCE795GA0DX )
other possibility L-BKLT_CTRL and L-BKLY-EN in PCH1D (COUGAR GP-U2-NF)

[Vogelek23]

You haven't a correct BLON_OUT signal (it must be approx. 3,3V). As jack155 said, please check (or replace) the Nuvoton KBC first.

[siddiq]

Hi everyone thanks for all the replies. I noticed that PIN 27 on the KBC was shorted to ground so i disconnected it and found out the short had vanished on PIN 5 of LCD connector. Also I connected 3.3v to PIN 5 and the backlight came on so it means the KBC has gone faulty. Thanks for all the help.