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MacBook Pro A2289 TouchBar (820-01987-A) - No power / No image

G

GeniusPlace

New member
PPBUS_G3H : 435 ohm

C8440 :
- pin 1 : 0001 ohm
- pin 2 : 0000 ohm

C8441 :
- pin 1 : 0013 ohm
- pin 2 : 0000 ohm

It looks like the U8400 heats up a lot too.
 
2informaticos

2informaticos

Administrator
Staff member
Very likely bad U8400.
To be sure, remove C8440 and check again.

BTW, save your time and do not measure again ground to ground points...
 
2informaticos

2informaticos

Administrator
Staff member
I didn't expect you to power up the board again.
Did you check diode mode to ground, once C8440 removed?

Happy new year too for you and all forum members!
 
2informaticos

2informaticos

Administrator
Staff member
Contact store staff for any doubt.
Chips should be the same, if is LP8548B1SQ and has the same package.
 
G

GeniusPlace

New member
Hello,
I removed U8400 and I replaced it. Unfortunately the MacBook doesn't turn on.

BTW,the diode value are stable :
C8440 : 0410 ohm
C8441 : 0399 ohm

What do you advise me ?
How are you able to check the diode value ? I mean, which tool do you use ?
 
2informaticos

2informaticos

Administrator
Staff member
MacBook should turn on even without U8400.
If not, you have more problems on the MLB.
Possibly overvoltage on 5V power rail damaged more things...
 
G

GeniusPlace

New member
Thanks for your feedback.
In this case, what would you do ?

What software do you recommend I use to check the diode values? I use XZZ or Refox, but it's incomplete...
 
G

GeniusPlace

New member
I would really like to repair this macbook but I think I don't have the right software or the right knowledge to do it.
So I joined this forum to learn as much as possible.

That's why I would like to know what software you used to guide me as our comments ? Because the software I use (XZZ and Refox) doesn't show me the diode values for MacBook. So I can't check if the values I have are accurate. Yet you were able to tell me if they were abnormal. I would have liked to know how you managed to find the right Diode Value ? :)

Also, you said me " Possibly overvoltage on 5V power rail damaged more things... ". Could you tell me what you would do first to check where the problem is ? Concretely, I would like to understand the systematics (the first things to do) in this type of case.

Awaiting your reply,
Many thanks
 
2informaticos

2informaticos

Administrator
Staff member
There is no software to show you the correct diode mode readings; apart of readings took from good working board.

You've said to get external video initially.
What happened from that moment until board died?
Wrong manipulation in the process, knocked off components; something must explain the overvoltage on the 5V_G3S power rail.

Does the board stay on if starts in SMC bypass mode?
 
G

GeniusPlace

New member
Ok, and which software do you recommend for bitmaps and schematics ? Currently I use XinZhiZao and Refox software, do you use another one ?

Honestly, I can't tell you more... I'm sorry.
What I do know is that this device was dropped off to us for a screen replacement. We tested sending the image to an external monitor, and it worked.
Then, I tested a macbook A1708 screen for my personal cultivation, and I didn't have any image on the screen.
After checking the motherboard, I know that it accepts 20V.
Then I check with the thermal camera, the T2 chip heats up very slightly (30°C/86°F), but no other component heats up.

Where do you recommend me to start on 5V_G3S ?

Could you tell me more about the Bypass SMC ?
 
2informaticos

2informaticos

Administrator
Staff member
Read here about SMC bypass and more information.

HOW TO collection

I hope this "How to" collection will help our members. I will possibly modify this post in time, if updates available. Trigger SMC_ONOFF_L (PMU_ONOFF_L): It reffers to simulate power button function, when the keyboard is not connected. We need to do this when we work with the board...
boards.rossmanngroup.com boards.rossmanngroup.com

I use Openboardview 8.0 to see boardview files and Acrobat Reader for schematics.

I can't really understand how the 5V_G3S got damaged in the process of screen replacement, other than bad manipulation; maybe battery wasn't disconnected.
 
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G

GeniusPlace

New member
In this case, for a macbook that no longer turns on, and for which we do not know the exact cause of the short circuit. What do you recommend that I do ? Where do I start to diagnose it ?
 
2informaticos

2informaticos

Administrator
Staff member
Once no very low resistance remains to ground after U8400 was removed, not easy to find another damaged chip.
I don't exactly know diode mode reading for a good working board at 5V_G3S, for comparison.
Changing chips one by one is a nightmare; maybe not worth to continue.
 
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