820-00923 20V @ 200mA not turning on

AJay_Smoothie

New member
I'd like to know what your input would be on this one. Firstly, I have above average circuitry understanding/skills but I'm definitely no professional. That being said I've never worked on MacBooks and I'm not familiar with how they work. I have an A1706 that had components R6907 & D6902 were physically burned, but everything else on the board looks perfectly fine. There is no water damage or any other visible damage. U6903 is happily outputting 3.3V after my toasted component transfusion, but the board won't turn on. It stays at 20V @0.2A and never does anything. Here the information I was able gather so far about this board.

PPDCIN_G3H = 20V
PPBUS_G3H = 13V
PPDCIN_G3H_CHGR = 20V
PP5V_USBC_X_VCC = 5V
PP5V_S4 = 5V
PP5V_S0 = 5V
PPBUS_HS_CPU = 13V

So those in my studies of this schematic seemed to be some of the main power rails for most of the voltage regulators on board yet I'm not getting any power to the following coils/vregs/lines


PP5V_S4_X_USBC = 0V
PP5V_S4_T_USBC = 0V
(I feel like these need to be on 5V for the TBT regulator...but they don't come on. Why not? The 3215 seems to be function properly otherwise? Just conjecture on my part)

LB700 = 0V
L7210 = 0V
L7410 = 0V
L7420 = 0V
L7430 = 0V
L8410 = 0V
L3500 = 0V

But all of those systems are getting their proper voltage inputs..... I know the TBT 5V has to be very important and it's not working.

I'm extremely stumped. I cannot find a common denominator between the power supplies, or anything to do with the burned components. Ideas?
 
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2informaticos

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

Your board turns on, as you get even some S0 voltages.
Not working properly is other thing; make difference between turning on and booting.
Power on sequence is not completed in your case.

"I feel like these need to be on 5V for the TBT regulator"
These are output voltages, which appear ONLY when external device is connected to corresponding USB-C port.

"I know the TBT 5V has to be very important and it's not working"
Be aware of wrong assumptions in the future.

L7270 voltage must appear before L7210/20; checked that?

L7410/20/30 will not get voltage untill high graphics load is detected; no reason to check them at boot.

L3500/B700 already explained.

L8410 is for backlight output; obviously not interesting at this moment.

Do you get voltage at L7900/60?
 

AJay_Smoothie

New member
Thank you for the quick response. That gives me some hope that I can get this thing fixed.

L7270 is at 1V
L7900 is at 1.2V
L7960 is at 950mV
 
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2informaticos

Administrator
Staff member
Post basic voltages for U7100; pins 41, 42, 48.
Do NOT try to measure on its pins; use surrounding components as test points!
 

2informaticos

Administrator
Staff member
We have many threads about BIOS; just search and read the forum.

You have to reprogram U6100...

BTW, any reason to quote an entire post visible few centimeters above (no matters how long/short is)?
Please, maintain forum aesthetic...
 

2informaticos

Administrator
Staff member
You may need an USB BIOS programmer, like TL866, EZP2019, CH341, etc...
I suppose you don't have Medusa programmer, which makes the job easy (not cheap tool).
 

AJay_Smoothie

New member
I have several CH341 programmers from my Arduino days, I should be able to figure it out. I'll give it a go and see what happens!

What would be the reason for needing to re-program it? IC's aren't supposed to just "forget". I couldn't find a direct link back to the initial burned components so I was just curious for information's sake.
 

2informaticos

Administrator
Staff member
Do NOT throw the money.
You need BIOS with clean ME region; not a file read from other similar machine!

Medusa programmer can do all the job onboard; recommended if you plan to repair MacBooks in the future.

UEFITool can help you to change serial number and clean ME Region.
However, you need to desolder/resolder the SPI chip (U6100) in this case.
 

AJay_Smoothie

New member
Well this is sad sad end to my repair attempt. I can't spend 350$ on a programmer and nobody has even remotely clear instructions on how to do it otherwise.
 

Eduardo&Macs

New member
Hey Ajay,

You don't need to spend $350 on a programmer. There are dozens of programmers that you can use for this job. You can find some for around around $30-$50 that'll do the job.

The way I've done this sorta job is use a programmer that connects to the JTAG connector on the board. Read the BIOS 3 times to make sure they all match and ensure a good read. Use UEFITool to clean ME region.

It'll take a little bit of googling but you'll figure it out. You do NOT need to remove an EFI lock. This is to clean the ME region of the BIOS which are two different things. I personally use the Medusa programmer but I believe it's possible to use the CH341A programmers with an adapter that fits the JTAG connector on the board.
 

AJay_Smoothie

New member
Eduardo,

Are you saying the only thing that needs to be done is to "clean the ME region" without finding another BIOS to upload to it? Or do I still need to find another BIOS/bin/file to re-write the chip?

I also can find any pinouts as to actually hook up the programmer. I have about 4 of them and would rather desolder the chip(U6100) and quickly make some connections to my existing programmer than having to buy adapters that I'll use once.
 
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2informaticos

Administrator
Staff member
"copied over the mac ROM"
What did you copy over?
I was expecting to just clean ME region on your board.

BTW, always make a backup of original BIOS; before erase, or overwrite it!!!
 
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