another 820-3662 no backlight after liquid on lvds connecor

[Dozer]

hello, need some help on this machine.

working so far so good, I can see everthing with a flashlight behind the LCD.

found red point under lvds connector, else white points everythere and board is looking good condition




the backlight pin on J8300 Pin 1 is away, replaced J8300 and a little jumpwire from pin 1 to net PPVOUT_S0_LCDBKLT

but still no backlight

tested:

F7700 good, both pins 11.8V

PPBUS_SW_LCDBKLT_PWR = 11.82V
PPBUS_SW_BKL = 0V

LCDBKLT_EN_L = 11.8V

R7701 = 80.5K
R7702 = 64.5K

should be ok

BKLT_EN_R (pin17 U7701) = 3.3V

U7701 pin 18 and pin 5 both 5.05V


SMC_Lid = 3.42V


Display from known working MacBook Pro 13 inch Retina Core i5 (Mid 2014) same result, a picture to see with a lamp behind the lcd


would u suggest to replace U 7701?


on R7758/57 i can see on the scope a data and a clock signal

 

[Dozer]

No Title

 

[peterfixit]

is that a hole? pull that shit off and find the short

 

[G.Beard]

Check resistance between ground and pin 1 on j8300 and are traces from pins 3, 4 and 5 OK?...

 

[jason_microsoldering]

No, no need to replace Q7706 if it isn't being told to open. Are you testing with a known good 2014 screen and cable (plugged in of course)? R7757/R7758 ok?

 

[Dozer]

peterfixit , no hole there, pin 1 is the trace burned, LVDS connector was 1. thing i replaced

G.Beard, no short from pin 1 to ground measured now in diode mode red on gnd 1.085, traces from pin 3 and 4 are ok

jason_microsoldering, i dont want replace Q7706 I ask to replace U7701?, Display from known working MacBook Pro 13 inch Retina Core i5 (Mid 2014) same result, a picture to see with a lamp behind the lcd, on R7758/57 i can see on the scope a data and a clock signal

 

[Dozer]

No Title

 

[Dozer]

dukefawks , you write here: https://www.rossmanngroup.com/boards/forum/board-repair-troubleshooting/2093-820-3662-no-backlight

that LCDBKLT_EN_L shold not be more than 3.3V, appleonarim had here the same problem he had 12V, I have 11.8V. but the threat is without soulution

 

[peterfixit]

now thats nice soldering, good one

 

[Dozer]

but the problem is still not solved :-(

 

[peterfixit]

its currently 220am in new york, so wait a few hours
have you read louis's backlight repair guide?

 

[G.Beard]

Good screen connected right?

I never bother to figure out what is wrong with backlight, I just replace everything that could have been affected by the short and get it out the door..... Sure it's the monkey no brain way of doing it but I really don't care because it works every time and I get paid for my 5 minutes.

5V on 30,29,28 J8300?
R7757/8 both 0Ohms?
R7708/09 good?

Replaced C8354/5... Just because they are close to fucked up burns on old J8300.
Check R7721/22?

U7750 OK?
Did you replace U7701?

 

[jason_microsoldering]

Wait, you are using a 13" display on a 15" board?? Are you sure that works?

 

[jgraffis]

That I've been told a 13" screen will not work on a 15" machine. i would suggest going over the pinned post on back light issues even thought its not a macbook air.

 

[jgraffis]

first think i would check is voltage on L7710. if pin 17 is ok and pin 5, pin 18 are all present then no boosting is happening on pin 2 of of L7710, then change U7701. please report back these voltages first.

 

[Dozer]

yes, i tried the 15" on the 13" and the 13" on the 15" nothing is working, so i am shure its not compatible.
pin 5: 5.05V
pin 17: 3.3V
pin 18: 5.05.V

L7710 pin 2 nothing is happening

the problem is i cant test if the screen or the cable has a problem.

i will report back how that case is ending soon