macbook Air 2015 820-00165A

Hi

Got a no back-light unit

Backlight circuit looks good

R5117 completely burned out thou, cant attach it back as both points are also burned out.
Any tips how to attach the replacement?

Closer inspection revealed that the Q5158 also has damage on the CPU_THRMTRIP_3V3 line
 
Last edited:

JohnB8812

New member
Those have nothing to do with backlight...what voltage do you get on BKLT output? There is a great guide on the pinned posts from Louis btw
 

2informaticos

Administrator
Staff member
Lot of information on the forum.
Especially 3437 and 00165 Air boards; just use search function.

Rebuild CPU_THRMTRIP_3V3 trace from Q5158 to SMC area.
Then solder R5117 to that line and wire its other pad to nearest 3V42 point...
 
ok

continuity between D7701 and A5 ball of U7701

(all voltages taken with screen connected, psu connected, no battery)

D7701 8.51V

Q7706 voltages
1 - 0.02v
2 - 0.02v
3 - 2.8v

4 - 8.5v
5 - 8.5v
6 - 8.5v


F7700 was ok but I shorted it while measuring voltage ( touched both the shield and the fuse - probe slipped :/ )
It had continuity before thou and no backlight so I am guessing that this wasnt the issue

Also I am getting a short to ground on PPBUS_G3H, when I hold the multimeter for a few seconds it kinda drains and short goes but when checked later - it does the same (is that relevant at all?)

Still have to work on that CPU_THRMTRIP_3V3
 

JohnB8812

New member
Are you measuring resistance with power applied??? I hope not as that's a good way to mess up your multimeter...if you have 8.6 you don't have any kind of short on PPBUS. Sounds like bad LED Driver to me. BKLT_EN resistors ok?
 
That was the case. I have learned something today :)
No short now
R7788 - 300koms
R7789 - 146 kOms
Looking fine

Will replace f7700 and investigate further
 

2informaticos

Administrator
Staff member
"PIN 2 according to the schematics, the other pin was 0v"
According to schematic, D7701 has two pins, A and K.
And is impossible to have 0V at same time with a voltage on these pins; unless diode is burnt!
 

2informaticos

Administrator
Staff member
Post diode mode readings on all conections of U7701; red probe to ground.
Also post BKL_PWM/EN voltages; LCD connected, of course...
 
ok

U7701

Pins

1 0.002
2 0.002
3 0.564
4 0.0
5 started burning - most likely I put the wrong probe on but cant say as I dropped it
disconnected from power and rechecked the f7700, will have to replace it again
Pin 4 is now in -1.8
Just thinking - was my mistake measuring it while powered on?
 

JohnB8812

New member
Do NOT measure diode mode with power applied! Replace F7700 and just replace the driver. Wasting time measuring when you?ll know right away if it?s the chip or not replacing it...
 
Hi again,

Replaced the U7701 as well as F7700, also changed D7701 as it was showing same voltage on both ends

now - still no backlight

U7701 readings

1 - GND 0
2 - GND 0
3 - 2.865
4 - 0.559
5 - 0.636
6 - 0.427
7 - 0.427
8 - 2.952
9 - 0
10 - 0
11 - 0.461
12 - 2.655
13 - 0? (not sure if its the right testpoint)
14 - 0.415
15 - 0
16 - 0.461
17 - 2.657
18 - 0.629
19 - 0.626
20 - 0
21 - 0.650
22 - 0.650
23 - 0.650
24 - GND 0
25 - 0.651

I hope something pops out for you :)

Also measured voltages on Q7706 while on with screen connected (picture present) - 0v on every point :/ so rechecked f7700 (gone again)
Replaced F7700 again and Q7706 readings as follow

1 - 8.01v
2 - 8.02v
3 - 2.63v (LCDBKLT_EN_DIV_L)
4 - 8.15v
5 - 8.15v
6 - 8.15v


Rechecked D7701, 8.15 v on both ends


Thanks for looking
 
Hi, thanks for the message
XW7720, all in order continuity present from pin 5 of U7701 and to D7701

U7701 voltages

3 - 2.84 V
4 - 2.57 V

11 - 5.12 V
14 - 3.34 V

Cheers
 
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