820-01958 no image and backlight

[kingskie]

Hi all,

i am working on macbook air 820-01958 that has water damage on connector J8500 around pin ppvout_s0_lcdbklt and dp_int_auxch_c_n and dp_int_auxch_c_p. i changed the connector but still no image and backlight.
already checked there is no short to ground on this line.

any suggestion will be appreciated.

thanks

[mon2]

Re: 820-01958 no image and backlight

During a normal boot attempt, are you able to toggle the key caps led on the keyboard? If yes, the operating system is booting and that is a good start.

[kingskie]

Re: 820-01958 no image and backlight

During a normal boot attempt, are you able to toggle the key caps led on the keyboard? If yes, the operating system is booting and that is a good start.

yes @mon2, the caps lock led on and when i connect to external all are ok, i can login.

[kingskie]

Re: 820-01958 no image and backlight

anyone can help? i'm stuck on this problem.

[mon2]

Re: 820-01958 no image and backlight

Measure the voltage to ground of the backlight enable pin. This will confirm if the logic board is requesting for the backlight to turn on or not.

Note, for the backlight to enable, the display must be detected.

What voltage do you measure for the backlight with the display connected?

Using your phone as a torch / flashlight, apply the light on the front face of the display. Can you view any of the standard graphics on the display?

[kingskie]

Re: 820-01958 no image and backlight

Measure the voltage to ground of the backlight enable pin. This will confirm if the logic board is requesting for the backlight to turn on or not.

Note, for the backlight to enable, the display must be detected.

What voltage do you measure for the backlight with the display connected?

Using your phone as a torch / flashlight, apply the light on the front face of the display. Can you view any of the standard graphics on the display?

hi @mo2,

sorry for the late reply.

voltage to ground for backlight enable pin on Q8400 Pin 3 is 2.07
voltage on this pin when plug the adapter is 12.46V
already try to use flashlight but cannot see any backlight or image at all.

[mon2]

Re: 820-01958 no image and backlight

Measure the voltage to ground readings for:

EDP_BKLT_EN
BKLT_EN_R

[kingskie]

Re: 820-01958 no image and backlight

measure the voltage to ground readings for:

edp_bklt_en
bklt_en_r

edp_bklt_en = 0.481
bklt_en_r = 0.481

[mon2]

Re: 820-01958 no image and backlight

So the display is not being enabled.

Remove all power. Meter in resistance mode.

Check the resistance to ground of these same signal lines.

[kingskie]

Re: 820-01958 no image and backlight

So the display is not being enabled.

Remove all power. Meter in resistance mode.

Check the resistance to ground of these same signal lines.

edp_bklt_en = 84 kohms
bklt_en_r = 84 kohms

[kingskie]

Re: 820-01958 no image and backlight

anybody can help?

[mon2]

Re: 820-01958 no image and backlight

In post #8, missed that these are diode mode readings, not voltage readings.

Meter in 20v or higher dc volts scale.

Measure each point to ground.

[kingskie]

Re: 820-01958 no image and backlight

In post #8, missed that these are diode mode readings, not voltage readings.

Meter in 20v or higher dc volts scale.

Measure each point to ground.

hi @mon2, i set the multimeter as you can see from the picture and red probe to ground and black probe to the measurement point.

CMIIW

[kingskie]

Re: 820-01958 no image and backlight

if you mean the voltage for these pins than all are 0V