820-3476-A - No image - [SOLVED]

[nameless]

Hey everybody and Happy New Year

I've got an issue with 820-3476-A board. Customer brought it after another shop repair attempt. The board had minor oxidation around jtag port and J8300.

R8317, R8318 and C8302 were knocked off. After replacing them I'm still missing some voltages:

MEASUREMENTS
J8300
Pin1 : 0V
Pin2 : 0V
Pin3 : 5V
Pin4 : 5V
Pin5 : 3.3V
Pin6 : 3.3V
Pin7 : 3.3V
Pin8 : 3.3V
Pin9 : 0V
Pin10 : 0V
Pin11 : 0V
Pin12 : 3V
Pin13 -> Pin30 : 0V

L8300
5V on both ends

U7700
Pin0 : 0V
Pin5 : 5V
diode mode
pin15 : 0.5
pin16 : 0.5

U8330
Pin1 : 0V
Pin8 : 3.3V

U8340
pin1 : 0V
Pin5 : 3.3V

Don't know where else to look but it seems that U7700 can't get enabled.

thanks for your support

And have a great 2023 !!

 

[2informaticos]

"Pin30 : 0V
..............
L8300
5V on both ends"
Broken trace???

Don't waste time with backlight searching; LCD is not recognized yet.

 

[nameless]

thanks for your reply

oh I forgot to mention all measurement were done without LCD connected

here how R8317, R8318 and C8302 are connected

now with the lcd connected, i'm getting :

on J8300 pin 12 : 1.5V
on L8300 : 0V on both ends

 

[2informaticos]

ALWAYS check voltage and signals on LCD connector WITH LCD connected!

L8300 voltage must appear in the first few seconds, when the machine chimes.
LCD_HPD_CONN must go high (2.5V) at same time; if not, 5V LCD (L8300) will disappear.

 

[nameless]

ok just replaced J8300 (to be sure)

L8300 go indeed to 2.5V for a few seconds (not 5V anymore)
LCD_HPD_CONN (C8353) goes high but very quickly, don't have time to spot exact voltage

 

[nameless]

now with the lcd connected and open lid I do get 5V on L8300

and 5V on pin 28,29,30 on J8300

 

[2informaticos]

You've checked first without LCD and next with panel closed (even LCD was connected)?
Please, put some logic in the repair process.
You can't expect image/backlight, if Hall sensor pulls down SMC_LID.

Use a flashlight and check if at least image is present.
It should, if now you have steady 5V at J8300.

 

[nameless]

true true

sorry having a hangover since yesterday

so when I plug the ssd and speakers I do have a chime and a backlight but no image and fan at max level

I do get
on J8300
40V on pin1
5V on pin 28,29,30

L7710 - 10V

 

[2informaticos]

Check all C8320-28 caps and their traces.

 

[nameless]

Indeed ! there was no continuity between C8326 pin2 and R8317 pin1

thank you @2informaticos

Great as always