820-00850 dim backlight

[kingskie]

hi all,

i'm working on macbook pro A1989 820-00850 that has dim backlight.
means only when set the brightness from 50%-100% then the macbook has backlight. below 50% is no backlight.
the board is clean, no sign of water damage.

already change the lcd but still the same.

do you guys had this problem before?

[mon2]

Re: 820-00850 dim backlight

Remove all power. Measure the resistance to ground of the backlight voltage pin.

Do try a PRAM reset.

[kingskie]

Re: 820-00850 dim backlight

Remove all power. Measure the resistance to ground of the backlight voltage pin.

Do try a PRAM reset.

PPVOUT_S0_LCDBKLT = 16 Mohms down to 6.6 Kohms down to O.L and circle again
PPVIN_SW_LCDBKLT_SW = 10 Mohms
LCDBKLT_FB = 151 Kohms
PPVIN_S0SW_LCDBKLT = 17 Mohms
LCDBKLT_EN_L = 77Kohms
LCDBKLT_FET_DRV_R = 20Kohms

i will try to PRAM Reset

[kingskie]

Re: 820-00850 dim backlight

after PRAM RESET the apple logo is birght until login screen. but after input the password and loading suddenly the backlight dim again until dekstop shows up.

[mon2]

Re: 820-00850 dim backlight

Sounds like a software issue.

If you remain on the login screen -> display is bright ? (do not enter the login details to test)

Can you test with a bootable USB media ?

If the USB media boots normal and maintains the high intensity then it is down to the OS settings for your display.

[kingskie]

Re: 820-00850 dim backlight

Sounds like a software issue.

If you remain on the login screen -> display is bright ? (do not enter the login details to test)

Can you test with a bootable USB media ?

If the USB media boots normal and maintains the high intensity then it is down to the OS settings for your display.

ok @mon2, tommorow i will try to boot with usb. if it is really software problem, is there a way to reset the setting without reinstall the mac os?

[kingskie]

Re: 820-00850 dim backlight

update

my bad i checked with different lcd...now try with the same type and the backlight is ok.

thanks @mon2