A1502 - No backlight - C8352 odd behaviour.

[samstown]

Hi,

Board = 820-3476-A

I've been reading backlight sticky post and looking at potential failure using the two pics with all failure listed but I can't fix that one.
There's no backlight, I see apple logo and login window if I apply light to the lid.

U8300 PIN1 = 5.14V
PIN 2 = 0V
PIN 4 = 5.14
PIN 6 = 0V
PIN 7 = 0V
PIN 8 = gnd

I've noticed that C8352 is "open" when power is off and becomes 0.10 (Diode mode) (EDP_PANEL_ POWER_OR_PSR_EN) 3 seconds after I connect to magsafe. When I measure with "beep mode", the multimeter starts to "beep" after 3 seconds when I plug power.


U7700 PIN 11 BKLT_SD = 12.4V
U7700 PIN 12 ISNS_LCDBKLT_P = 12.5V
U7700 18 PP5V_S0_BKLT_A = 5.13V
U7700 17 BKLT_EN_R = 5.14V

D7710 = 0
Q7701 5 = 0 PPVIN_SW_LCDBLT_SW

R1430 - EDP_BKLT_EN = 0V

Thanks
Sam

 

[2informaticos]

"When I measure with "beep mode", the multimeter starts to "beep" after 3 seconds when I plug power."
How many times we said on the forum NEVER ever check diode mode, or ohm scale with power applied???

Any history available?
Did you test with known good (2015) LCD assembly?

 

[samstown]

the guy said he was in NY and screen stopped working suddenly.

I don't have another A1502 at the moment but I can look for one.

 

[samstown]

I've asked but so far I haven't find A1502 to test.

 

[2informaticos]

You don't need fully working screen.
Broken screen, with confirmed working backlight is good enough for test; and something good to keep.
Try to get one from other service shop, or online auction.

 

[samstown]

Hello

Took me a while but I finally found a cheap A1502 with working screen.

I've installed faulty motherboard and the problem is the same, so the issue in not the screen.

Any idea what i should look for ?

thanks

 

[2informaticos]

I don't know where was my mind.
I just saw you have 3476 board, which isn't 2015 year.
So get 2012-14 screen for test.

I apologize for my mistake...

 

[samstown]

no problem but a working A1502 should be ok?. I installed the fauly motherboard and it's the same problem, I see the icon if I apply light to the lid, so it's not the screen.

 

[2informaticos]

So you can confirm, no backlight with known good compatible (2012-14) LCD assembly?

Do PRAM reset 2-3 times.
Check R7750-53 and their traces.
Post diode mode to ground readings at D7710 (both) pins, w/ and w/o LCD connected.

 

[samstown]

Thanks.
PRAM reset 2-3 times. - DONE, no change.

Check R7750-53 and their traces.
traces are working, resistor seems to be ok.


D7710 without LCD
PIN 1 = 0.977
PIN 2 = 1.575

D7710 with LCD
PIN1 = 0.969
PIN2 = 1.550

 

[2informaticos]

Check if you get any pulse to 30-40V in the first seconds at backlight output (when hear the chime).
Try changing U7700.