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Macbook Air A1932 820-01521-A No boot, 20V it goes to 0.45A then power cycling

P

PACh

New member
Hi all, Im new to the forum and trying to learn to repair macbooks.. :)
I got this macbook air with the trackpad click not working, the fuse was blown (its never the fuse) I tested the line and seems ok, replaced the fuse and it worked again... all good BUT when I tried to remove the board again I pressed the reset switch next to the battery connector WITH the USB-C power still connected to the board.... I pressed and kept pressed for some seconds twice because the fan started to spin... then I realized why.... After that the machine wont boot, It gets 20V and start booting it goes briefly until 0.5A the returns to 0.45A and stays there, after some seconds it restarts the boot process again, I dont get anything on the screen. the CPU start to get warm and fan starts spining...
The switch SW6955 still gets 3.3V
All the SLPS2R are with te correct voltage.
PVDDCPUAWAKE_SW0 to SW3 when booting 0.97V then goes to 0.55V and stays there

PP1v2_S0SW: 1.19V

PP1v_S0SW: 1V

PPVCCIO_S0_CPU: 0.95V

PPVCCSA_S0_CPU: 1.1V

PPVCORE_S0_CPU: 0.84V

PPVCCGT_S0_CPU: 0V

ALL_SYSPWRGD: 1.8V

Trackpad click still works, no green light on keyboard, if I connect an usb to the usbc it gets light for a second

Thank you in advance

 
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2informaticos

2informaticos

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

L7210/30 voltage starts with 0.84V and remains stable?
Caps Lock light reacts pressing the key?
Did you try DFU?
 
P

PACh

New member
Thank you for your reply,
L7210: yes stable (in both pins)
L7230: yes stable (in both pins)
No Caps Lock green light
It wont go to DFU by itself or by pressing the keys combination (DFU never appears on configurator 2). It will reboot after few seconds anyways as you can see on the video.
Screen always black.

L7230: 6.5 Ohms
L7210: 6.5 Ohms
L7430: 5 Ohms
L7410: 5 Ohms
L8102: 52.4 Ohms
 
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2informaticos

2informaticos

Administrator
Staff member
This machine should be detected in DFU.
Did you exactly follow all the steps in DFU tutorial?
Be sure to use the correct USB-C port.
 
P

PACh

New member
Ok after many attempts i managed to go to DFU. I comes with a lock and tellsm it has to update the system. The problem with this is that I dont want to update the BridgeOS ;)
is there a way? like flashing the T2 ROM or other chip?
 
2informaticos

2informaticos

Administrator
Staff member
"I comes with a lock and tellsm it has to update the system."
What kind of lock?
You should get padlock icon once DFU ends.
 
P

PACh

New member
yes thats what i mean a padlock icon, I tried and the same not boot... could be dead CPU? it gets warm then power cycles...
*now i get the sound when i connect the usb-c power before I didnt get that sound...
Battery charges
 
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2informaticos

2informaticos

Administrator
Staff member
Check for USB activity and external video.

BTW, if you get padlock icon, that means DFU was completed and BridgeOS is now upgraded.
 
P

PACh

New member
BTW, if you get padlock icon, that means DFU was completed and BridgeOS is now upgraded.
Click to expand...
:-/

Tried but no external video - *It was in recovery mode need to install OS so I dont think I can see external video in that stage.
If I connect a usb stick or a mouse its light flashes briefly but not like reading activity
 
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P

PACh

New member
how can i check if the CPU is dead on this board? (i have an osciloscope) I want to discard that, so I know there is hope and i can keep searching for a fault.
Im concerned about this:
L7230: 6.5 Ohms
L7210: 6.5 Ohms
L7430: 5 Ohms
L7410: 5 Ohms
L8102: 52.4 Ohms

I dont know if those values are ok in thins board (820-01521-A)
 
P

PACh

New member
it goes streight from 0v to 0.844 when USB-C starts pulling 0.4x Amps then stays in 0.844-0.845 until power cycle then starts over. Something makes it reboot...
 
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P

PACh

New member
Do you know which are the equivalent to the lines: LPC_FRAME_L, LPC_CLK24M_SMC in these T2 machines?
I want to try the troubleshooting method that checks the wave form on those lines, I want to check if it is the CPU
 
2informaticos

2informaticos

Administrator
Staff member
LPC bus is not used anymore now.
The corresponding PCH lines are now used as SPI bus, between T2 and PCH.

CPU core voltage is dinamically adjusted.
PCH, CPU and BIOS (T2) are involved there.
And BIOS can only be (automatically) reflashed in DFU.
 
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