a1502 820-4924-A Liquid Damage... no image, but boots when Magsafe plugged in

[papalati]

TLDR - Early 2015 MBP Retina was dropped and had liquid damage as well. When plugged in it turns itself on until manually forced off. No display and no external on hdmi as well.

Long story, bought a 13" a1502 Early 2015 and figured it had been dropped based on the listing. Little did I know it was dropped and had liquid damage in the corner near the lcd connector. The indicator in the middle of the board wasn't triggered. It arrived and I plugged the power in and it turned on by itself.

I'm assuming a short somewhere, but the screen stayed pitch black. I should have tried the flashlight trick to see if the backlight was out, but already had the board out by the time I remembered that as I wanted to try a known working board I had in it. The other board worked fine with the magsafe and also the screen obviously.

I've checked the board and the only thing I can come up with so far is a faulty FDC638APZ IC but still waiting for the chips to come in. So, I'm not sure where to go from here on the magsafe triggering the laptop on. Was considering putting it in my ultrasonic to clean it up before I get started again tracking down the issue.

What do you guys think?

 

[2informaticos]

"a faulty FDC638APZ IC "
You should mention schematic position, not component model.
Then we can make more exact idea about what you talk...

Test the board alone on the desk, only charger connected.
Need one USB device, if you get voltage on the CPU coils. to check for USB activity.
Dropped board is always nightmare; adding liquid spill, you are probably wasting time on it.
As is your personal machine, you can gain experience with it at least...

 

[2informaticos]

"In boardview it shows only a 5 at the bottom of the chip for the pins, but from left to right ..."
You make the things to look more complicated than they are!
Use signal names from schematic/boardview; this way avoid any confusion.
You do NOT need to mention any space direction, you are not examined for driver license here.
Our help is based on the information provided by you; so be more clearest posible, please.

As for example,
"At Q7701
From left to right, 1st pin = 145.6 "
there is in fact pin 4/Q7701, which MUST be mentioned as LCDBKLT_FET_DRV_R.
I have no idea if you posted a value measured on ohm scale, or diode scale (expected).
ALWAYS start measuring in diode scale, red probe at ground; sometime need to invert probes, for second reading!

On the other side, I wonder how can you get different readings in the same line¡¿?!
"2nd pin = 2.08, 3rd pin = 97.3, 4th pin = .47
----------------------------
2nd pin = 1.92, 3rd pin = .53, 4th pin = .53"
There should be LCDBKLT_SW, if your space reference is correct.
I don't talk about board differences.
In the same board, these three pins MUST get same reading; as all are connected to the same rail.

"Need one USB device, if you get voltage on the CPU coils. to check for USB activity. "
Do NOT waste the time searching for image/backlight, if you do not get voltage on CPU VCORE coils (L7310/20).
USB activity is also required to be confirmed first...

 

[2informaticos]

"No display and no external on hdmi as well "
That is the reason I asked about USB activity.
Missing internal and external video at same time, looks more like stuck board.

"As stated before, the computer boots to the chime even on the bad board "
NO, you've mentioned about ANOTHER working board, tested in the same case.
"The other board worked fine with the magsafe and also the screen obviously "

I'm really sorry if you got annoyed, was not my intention.
I just wanted to mark your wrong assumptions.
If you consider that is not for you help, dismiss such advise.

We try to start again.
First confirm USB activity on the first (bad) board.
Chime is not always sufficient.; board can get stuck after chime, before sending any image.
You've reported missing internal/external video at same time and is not too much reason to suspect a problem with backlight.

"I wanted to first find out how to fix the fact that when you connect an ac adapter to it the computer boots by itself. "
Not first, nor last.
I didn't say anything about that before, as it is normal behavior for any iCore MacBook.

 

[papalati]

I think it might be your word usage and the use of your CAPS as it comes across as you scolding/yelling at me, when all I'm trying to do is seek some help. On top of that I am also having trouble understanding your English at times as well. It is very blunt and brash, but please understand that I do appreciate the fact that you've taken time to at least reply to me when no one else has.

As you said, let's start again.

Could you please elaborate on what you mean by stuck board? As the term stuck is very vague.

I will test for usb activity and voltage on the cpu coils and get back to you with that.

 

[2informaticos]

Any news about this?

 

[papalati]

Any news about this?

Working on it now. Hope to have some kind of information for you today

 

[papalati]

Getting 1.87 on CPU VCORE coils (L7310/20) with usb mouse plugged in and is getting power.

 

[2informaticos]

VCORE looks good.
Do you get USB activity now?
Disconnect/reconnect USB mouse when board is turned on; mouse get steady light again?

 

[papalati]

Yes, the mouse gets steady light even when disconnected and reconnected.

 

[2informaticos]

Seems that you now have USB activity.
Test for external video, if the board is out of chassis.

 

[papalati]

No external video on both DP ports on bad board.

Tested same setup and getting signal from good board.

So definitely no external video signal being sent to the monitor on bad board.

Yes, the board is out of the chassis.

 

[2informaticos]

If there is USB activity for sure, you have a problem with Intel graphics.
And shouldn't be related only with internal, or external video outputs, as both are missing.

Did you take a photo of the liquid affected areas, before cleaning the board?
Some return from backlight voltage could have been killed the iGPU.
When you start the board with internal LCD connected, check for voltage at R8320 pads.
You should also get voltage there in the first few seconds at least, even without LCD.
Keep the multimeter probe connected there when turn on the board; especially when hear the chime...

 

[papalati]

Haven't put the board in the ultrasonic yet, Crest sent me the wrong one and it's too small.

Finally got it under the scope and there is heavy corrosion inside both display ports and only the liquid damage indicator by the lcd connector is activated. The others are still white. It's like someone dipped the corner of the laptop in water near the lcd connector.

I'll do the other tests later tonight or tomorrow and get back to you.

 

[papalati]

Well... I went piece by piece through the board through the scope and found corrosion also on one other little piece and apparently a very important one as after I scraped the corrosion off and checked for continuity external video has been restored with a question mark folder showing

I think it's the power delivery system for the video maybe? Not sure since I don't read schematics obviously. Going to put it back in the chassis and test again.

I'll attach a pic from board view of the questionable point on the board.

 

[papalati]

Okay another update.

External Video is only working via the DisplayPort. Also, tested the IO board for the USB and HDMI and no signal coming from the HDMI port and no USB activity either.

Going to try and figure it out while waiting for your feedback