820-01958 dead after an attempt to update, no boot, no dfu mode - SOLVED

hjpl

Member
Hi, this MacBook stopped working during an update.
Connected to the power supply I have 20v and 1.93A but after a while drop to 0 and start again. It's not recognized in DFU mode.
With the board alone on the desk I have 20V and about 0.50A to for about 20 seconds, then to 0.24A for a while, then to 0 and start again.
The board is clean, no visible damage.By checking the start sequence the only different value I found is PPVDDCPU_AWAKE 0.5V, diode mode 0.018 Ohm and there is a short.
What is the best way to find the culprit?
Thanks for your help
 
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2informaticos

Administrator
Staff member
First of all, welcome to the forum!

I doubt you can measure 0.018 ohm in the board; that means 18 miliohm.
Compare the value with working board; can be correct in fact.

Did you try DFU with both charger and battery connected?
If still not possible, reflash SoC ROM (U4770) and try again.
 

hjpl

Member
Thank you!

Sorry, I mean
PPVDDCPU_AWAKE 0.50v, diode mode 0.018
but I have a short to ground in this rail (isn't that important or did I miss something?).
From schematics this line has to be 0.625-1.06v.

Yes, I tried Dfu with charger and battery connected.
I read about SE032 pad to force Dfu but I'm not able to find it. Can it be useful?
 
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2informaticos

Administrator
Staff member
"I have a short to ground in this rail
---------------
Compare the value with working board"
0.018 may be a good reading...

This board doesn't have pads to force DFU; SE032 doesn't exist.
Be sure to follow all the steps from DFU tutorial.
If still not possible, reflash SoC ROM (U4770) and try again.
Don't forget to make backup...
 

hjpl

Member
"I have a short..."
I said that because In test mode all the components on the PPVDDCPU_AWAKE line give a continuous beep (on both side), can this be normal?
Sorry if I insist but it seems strange to me.
I really appreciate your help.
 

2informaticos

Administrator
Staff member
A multimeter beeps until 0.050-0.070 in buzzer mode; depending of model.
That doesn't mean to be short.

Powerful CPUs and GPUs core may have just 1-3 ohm resistance to ground.
An i7 3rd generation has 1 ohm as normal.
Do you really think that working board with such low value has short to ground???
Don't make wrong asumptions so easy!

I just found 01521 Air 2018 board; very similar to your A2179.
And I got 0.016 diode mode reading there.
On this board, CPU core shows 0.013 (L7210) and iGPU only 0.010 (L7410) in diode mode; no short, believe me...
 

hjpl

Member
Of course I believe you, I just needed to understand the mistake so as not to repeat it in the future, thank you very much.

So I entered into DFU and chose reactivate option but in the end it gave me the error
"libusbrestore error:2015"

Now the board is stuck at 20v and 0.03a, it doesn't react to the power button (neither shorting SWE10) and it doesn't enter DFU mode.
PP3v3_S5 0v
PP1v8_SLPS2R_PMUVDDGPIO 0v
Should i go ahead with the U4770 reflash?
 
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hjpl

Member
I believe i got all sorts of dfu error messages but after tons of tries the machine decided to boot.
Thanks Informaticos, if you come to Rome, you are my guest!
 

hjpl

Member
After writing the original serial number the macbook appears directly into AC2, without typing DFU keys sequence and does not complete the restore returning the error "gave up waiting for device to transition from DFU state to DFU state".
 
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2informaticos

Administrator
Staff member
So you've completed DFU after flashing U4770?
Change serial into SoC ROM and see what happens.
Yoy can also try again DFU with original dump; it may work if try more times.
 

hjpl

Member
Sorry, I edited the question before reading your answer.

Yes, after flashing the SoC ROM I was able to complete the DFU restore.
Then I edited the serial and now ... (read post above)
 

2informaticos

Administrator
Staff member
You've said needed many tries to complete DFU after flashing new SoC ROM.
Did you also try many times with original dump?
Flash backup again, not only serial changed in new dump...
 

hjpl

Member
So...there was some dirt under U4770.
After cleaning, re-soldering and reassembling everything, I was able to complete the DFU restore but nothing happens at the end:
black screen, no caps lock, 20v up to 0.10/20a then to 0.01 for a few seconds and stops at 0a.
Several attempts, same result even without battery.
 
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hjpl

Member
The rom is the one you gave me to which I changed the serial (with this rom the device worked before changing the serial).
The battery is in good condition.
 

2informaticos

Administrator
Staff member
"I believe i got all sorts of dfu error messages but after tons of tries the machine decided to boot."
Did you get image, or USB activity that time?
 

hjpl

Member
Then I replaced the serial with the original one and restored again in DFU mode with the result described above (20v with 0a, no image or activity).
I've reset several times and in a couple of cases the fans started spinning but no image.
I tried the restore again but now appears directly into AC2, without typing DFU keys sequence and does not complete the restore returning the error:
Unexpected device state 'DFU' expected 'Recovery' (Probably forced into DFU mode externally) [com.apple.MobileDevice.MobileRestore – 0xFAE (4014)]
 
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