82-3437-A no backlight

[NicolasColsoul]

Hello guys,

First thanks for all videos, it's fabulous to give a second chance to a lot of Apple products. Thanks Louis !

Here, I'm coming with a Macbook Air 2013 A1466 820-3437 A with no water damage (really, I never seen a computer as clean) !

I take some measures with my (very very bad) multimeter around LP8550 : BKL_PWM was about 0.06V so I shorted to PP3V3_S0 and is now 3.3V.

All measures are shown. BKL_EN looks a little bit low but I think it's my multimeter because I won't measure 8.46V as PPHV_S0SW_LCDBKLT but boost won't work, I agree.

I can't probe feedback track without removing LP8550 because I don't find any via... (They don't exist on my pcb version ?) Ho may I do ?

D7701 isn't shorted.

PRAM reset is done.

What I'm wrong ?

Sorry for my English, I'm a little Belgian guy !

Regards,

Col

Bonus : the ugly short

 

[Alan.L]

you soldered to a wrong test point. replace the chip and run a jumper from FB line to PPHV_S0SW_LCDBKLT. (check if you have continuity before you do this)

also, your soldering bob is too big and that looks like a mess you are creating a short.

to

 

[2informaticos]

"BKL_PWM was about 0.06V so I shorted to PP3V3_S0 and is now 3.3V."
That is VERY-VERY BAD idea; you just injected 3V in a PCH pin!!!
For this (force) test, you MUST remove R7704 and inject 3V at C7704.

A5 ball has a very small surface near chip; scratch it and check continuity to D7701.

Do you get image at least?
Did you test for voltage at pins 14, 18/19 of J8300?

 

[NicolasColsoul]

No Title

Thanks guys !

So I removed my jumper first... Now, LCDBKLT_BOOST is 8.52V and PPHV_S0SW_LCDBKLT is 8.46V with screen.
I don't want to replace if it's not really needed
I just scratch around FB and continuity probe to PPHV_S0SW_LCDBKLT : it's ok.

Pin 14 : 2.47V
Pin 18 : 3.31V
Pin 19 : 3.31V ofc

More pics :

:

 

[NicolasColsoul]

I think the problem is BKL_PWM but I don't find where it will be generate...

 

[2informaticos]

"For this (force) test, you MUST remove R7704 and inject 3V at C7704."
If you get backlight, check again EDP_BKLT_PWM.
If is now high, remove 3V from C7704, resolder R7704 and test.
Also check resistance to ground on EDP_BKLT_PWM; you could already f***d PCH output...

If no result, change U7701.

 

[NicolasColsoul]

I just change U7701, nothing more happend. All voltages still the same.

Resistance to ground on EDP_BKL_PWM is about 168R (I don't know the precision of my multimeter).

Enabled is still a little bit low (not really 3.3V) and PWM is 0V but if i short to 3.3 (without R7704), nothing more happen.

Thanks !

 

[2informaticos]

"Do you get image at least?"
???

Did you try other LCD assembly?

 

[NicolasColsoul]

Yep, I can see the connection interface. I already try another LCD screen and it's the same problem.

 

[2informaticos]

Post resistance to ground on all connections to U7701.
Use nearest components as test points.

 

[NicolasColsoul]

I try do to my best :

 

[2informaticos]

We use diode mode for this.
Compare with attached notes...
LP8550.txt