820-3437 no backlight

[arnonabuurs]

Hi guys, happy new year! I have a 820-3476 with no backlight (can see the apple logo with flashlight). The board seems not to have liquid damage looks very clean also the area round U7700 and LCD Connector. I get 12.61v on pin 9/10. I did notice I have no voltage on the backlight Enable pin 17, what should this be? R7742 = 0 ohm. Any suggestions?

EDIT: Some extra messure i did:

C7717 pin 1 = 5.17v
Q7700 pin 3 = 12.51v
Q7700 pin 4 = 12.61v
Q7700 Pin 1/2/3/4 = 0v
R7701 = 80.3k ohm
R7702 = 63.5k ohm

So i figure the enable signal is not working for the backlight, please correct me if im wrong in my assumption

 

[dukefawks]

No idea what this is. Is it a 3437 or a 3476? Pin 9/10 of what, where?

 

[arnonabuurs]

This is a typo in the title its a retina 13 inch 820-3476, I cannot change the title anymore sorry.

 

[dukefawks]

If there is no liquid damage first try a known good LCD. If that works it may be a bad LCD cable.

 

[arnonabuurs]

Yes tried with 2 working LCD both no backlight

 

[dukefawks]

Sure these are 2013/14 LCDs? SMC_LID high?

 

[arnonabuurs]

Yes one of them belongs to this Mac board and works with another working board (3437 as well). SMC_LID 3.43

 

[dukefawks]

Oh now it is a 3437 again?
PRAM reset? What is the voltage on the backlight pin on LCD connector?

 

[arnonabuurs]

Sorry its so hectic here my brain sometimes struggles with all data .... it is still a 820-3476 Retina last time i checked .

Voltage on LCD Backlight Pin is 0, checked continuity between C7717 to pin 1 = ok and no short to ground (reads 0.761v on PPVOUT_S0_LCDBKLT). I think I have tried PRAM already but i can try again.

 

[dukefawks]

Diode mode on pins 3 and 4 of LCD connector?

 

[arnonabuurs]

Pin 3 & 4 both 0.438v

 

[dukefawks]

At this point I would swap the backlight IC.

 

[arnonabuurs]

OK will try that let you know the result