Macbook Air 802-00165-A Good backlight fuse, bad wled?

[brooke.j]

I plugged the display back in and no backlight fuse blew. When I first turned on the computer pin 3 of connector was at 7.6v then slowly it went down to 1.6. Do you still think this is due to the display?

 

[aprendiz]

The reason of a blown fuse is because a short on that line, this is why blew the fuse as you described on post #12...

Still think it is a bad display and/or cable..

 

[brooke.j]

cool thx I'll see if I can pull a screen. I wish there was a spreadsheet on which screens you can interchange. Google fu is not turning up many hits.

 

[larossmann]

any air screen can work on any other air. do not substitute a screen from any other unibody macbook or retina here or it will fuck everything up.

 

[brooke.j]

Thx Louis I remember that now from one of your videos. Wasn't going to even try because I do watch and listen.

 

[brooke.j]

Well new screen and still no backlight. Ugh.... Anything else I could try?

 

[dukefawks]

Right lets start over here.

What is the voltage on pin 3,4 on LCD connector. LCD plugged in of course on not with the lid closed.

 

[brooke.j]

Which is crazy because I was getting 3.4v. Maybe I just murdered the WLED and didn't know it?

 

[dukefawks]

Do you have an LCD plugged in while measuring? Also check SMC_LID

 

[brooke.j]

I have the LCD Plugged in. SMC_LID is 3.4v, PIN 3,4 of LCD is 8.5v. So it looks like the lcd is getting too much?

 

[brooke.j]

Ok so I'l start over. Thank you again for all the help. This is with the LCD plugged in.

Q7707 PIN 2 = 3.4v, PIN 5 = 3.4v
LCD connector PIN 3,4 is 8.5v
SMC_LID = 3.4v
Q7706 PIN 3 = 2.8v (close enough right?) PIN 1,2,5,6 = 8.5v

 

[dukefawks]

That all looks fine. Now check BKL_EN and BKL_PWM.

 

[brooke.j]

I've also cleaned the dam WLED driver too much and now if I wanted to replace it I don't know which way it goes. Can anyone help with that? Thx

 

[brooke.j]

Oh I can figure it out from the data sheet (I hope)!!

 

[dukefawks]

You have the board view for that. Please measure what I asked.

 

[brooke.j]

Ok I didn't see that post sorry I'll check those. Just a thought... there is only one LP8550 on mouser? Just want to make sure I got the right one. The numbers on top are different than on the original WLED.

 

[brooke.j]

BKL_EN = 2.8v BKL_PWM = 0.3v
Measured at PIN 1 of R7715 and PIN 2 of R7704 respectively

 

[dukefawks]

BKL_PWM should be higher. Do a PRAM reset to be sure it is not that first. Then check resistance to GND on BKL_PWM.
If that all seems ok, remove R7704 and connect BKL_PWM to 3V somewhere, like C7711 and see if that brings it back.

 

[brooke.j]

Thanks duke for hanging in there with me. I'll get on that right away. This forum and you super awesome!