820-3332 No backlight

[Bouba148]

No History, Came from another store, had L9000 was missing, soldered it back: NOK
Displays on external HDMI screen OK
NVRAM Reset: NOK
Had Flux around Q7080 and R7020 area
No sign of WD but some few Test Points near R2655 turned slightly brown like some screws holes contours......

PPBUS_S0_LCDBKLT_FUSED: 12.56V
LCD_BKLT_EN: 0V

IG_BKLT_EN = LVDS_IG_BKL_ON: 0V
IG_LCD_PWR_EN = LVDS_IG_PANEL_PWR: 3.353V

U8900 is powered properly:
PPVIN_S0_GFXIMVP: 12.56V
PP5V_S0_GFXIMVP: 5V

 

[2informaticos]

Do you get image on internal LCD?

If get external video, U8900 is good for sure.

"L9000 was missing, soldered it back"
5V for sure at pins 28-30 of J9000?
Also check LCD_HPD level.

 

[Bouba148]

It's hard to tell if I have an image on the LCD screen as the apple Logo is not transparent on this model, so when I put my torch on the apple, I even can't see the light on the screen.
However I 've put the torch on the screen directly and for me there's no image on the screen.
I had No 5V at pins 28-30 of J9000.

I don't know what happened but the backlight came back for no reason.......

I've reassembled the machine did few tries, it's like when the machine is upside down it's working properly but not everytime when in normal position.....

Also I've turned off the machine normally from the OS, tried to turn it back ON, it displayed the red low battery logo ( which means backlight OK ) with the fans spinning few seconds.....and this with the battery fully charged at 100%.
This machine is acting weird:
I've plugged the charger and turned ON properly with the backlight OK and the battery back at 100%....then the backlight went off....
this machine has really a strange behaviour.....

 

[Bouba148]

After different test I think that it's not a backlight issue but a CPU issue as I've noticed that when the backlight turns OFF I'm loosing the Image also.
I've noticed that sometimes, when I'm trying to turn OFF the machine from the OS, the Image and backlight turns OFF but the fans stay spining and S0 state is still present, I've to press the power button or disconnect the battery to turn OFF the machine....
So I'll focus more on the CPU and see if I can find something........

 

[Bouba148]

When this issue happens during the shutdown, I told you that S0 state was present, sorry but it's only present for CPU VCore, but I have no rail present for the GPU S0 states:
At those coils I have no power: L8360,L8310,L8930,L8960,L7550,L7560.

I'm looking for the common point of all those rails.......

 

[Bouba148]

I'm quit lost on this issue, and I don't really understand how the display/backlight is managed by this architecture......
I've noticed that even withh the display/backlight working, I have NO power on those GPU Coils/Rails I've mensionned before......2Informaticos could you please explain me (us) how it works on those machines with U8900, U8000 U9100 please?
Which one is doing what in which order/ sequence.....thank you

 

[2informaticos]

"I had No 5V at pins 28-30 of J9000."
In such case, no image possible; also no backlight, of course.

Be sure to use original charger and check SM_LID signal.

"could you please explain me (us) how it works"
The forum is most for repair assistance.
Louis staff provide online training, as in person too.
Many times I explain things on the forum, but training is better person-to-person...