[SOLVED]another 820-2915 with no backlight

[Dozer]

hello, i just working on that machine.

it has no backlight. with a lamp behind the apple logo i can see its working. i tryed to brighten up the display in osx but its full bright.

i found a bridged F9700 !

i pulled u9701 and there were 2 shorts (pin4-5) and (pin2-3)

after soldering a new one

still no backlight

feedback trace is not burned.

lvds connector replaced with a good one, only to be shure

pin 32 LVDS connector has 12.5 V only


and it seems that the gpu (untouched) is getting very warm

5V, 3.3V on u9701 is there

bkl_en = 3.3V

SMC_LID = 3,45V


display tryed with another board is working. need some help please.

thanks

 

[dukefawks]

BKL_PWM checked?

 

[Dozer]

No Title

yes,
it has 0.09V

the signal loooks a little bit not nice




the ppvcore_gpu is switching from 1.12 to 0.91 during the gong so the gbu what i thought should be working

 

[dukefawks]

0.09V is of course way too low. Remove R9704 and inject 3V directly, could be dead LP8550 pulling it down.

 

[Dozer]

thanks.

so direct injecting without R9704 is working good backlight

I measured R9704 it has 42Ohm a little bit to much
I measured R9704 Pin 1 in diode mode is short to gnd

pulled out still R9693 but still shorted. so that means the GMUX is killed?

(under u9701 was a short between pin 4 and 5, so the LCD_BKLT_PWM from the GMUX was directly connected to PPVOUT_SW_LCDBKLT_FB)

 

[dukefawks]

MUX is dead. Just leave PWM connected to 3V, just no brightness control.

 

[Dozer]

i offered my custom that but he want to have brightness control. I replaced the MUX and its working everything like it should. so the case can be closed. Thanks for you help.