MacBook Air M1 A2337 (13" 2020) Recovery mode boot loop

prodigy83

Member
This computer acts like the power button is being held down, but the power button is not held down at all. The power button actually does not even work. I hold it down to power the computer off, but it does nothing. I have tried disconnecting the power button to see if this does anything different and it does not. I have already tried formatting with disk utility, showing all devices too, formatting each. This still is not working. Big Sur (one of the default images) seems to install fine, but it just keeps boot looping after the install after it restarts. If I try to choose another boot disk (boot to the hard drive) I get the pictured error. I have even installed Monterey on a USB drive and the install went fine but again, it keeps boot looping in to recovery mode. I do not see any damage under the scope to the logic board. The customer that brought it in thought that there may have been some update being done and it never finished but she was not certain. I need some help with this one please.
 

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2informaticos

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Check PMU_ONOFF_L level w/ and w/o audio flex connected.
Also test using SWV012/13 pads instead of power button.
 

prodigy83

Member
Get this, I went to test the voltage for SWV013, and nothing. I noticed though that while I had it hooked up to the USB-C meter, it was only pulling 5v. Before I could have sworn that I was pulling 20v. Anyhow I placed the board back in the mac, hooked up the main things like screen, battery, trackpad, and I opened the computer, the computer actually booted up and went right back to the same screen. Maybe we are just not getting enough power for some reason. I have never seen a computer boot with only 5v. I guess I should look next at the CD3215 boot up sequence?
 

2informaticos

Administrator
Staff member
The main power supply since 2016 is buck-boost converter.
So it can work with just 5V.

Try DFU, if possible.
 

prodigy83

Member
Wow, I did not know that. DZF684 is missing! While inspecting, looks like something broke off. I will see if I have another and try again tomorrow. Let you know then, thank you very much.
 

2informaticos

Administrator
Staff member
Compare diode mode to ground readings between USBC1_USB_BOT_N/P and USBC0_USB_BOT_N/P lines.
May help to compare with corresponding USBC0 lines too.
 

prodigy83

Member
No dice. I found another Diode from board 820-00840-A part D3413, but I get OL when measuring after the replacement. I used this part since it matched up as being one of the "USBC_XB_USB_BOT_P" parts. Does this part matter which way I solder it down?

Measuring the USBC1_USB_BOT_P I get OL, but when measuring USBC1_USB_BOT_N, I get .732 in diode modes.
USBC0_USB_BOT_N is .745
USBC0_USB_BOT_P is .746
 

2informaticos

Administrator
Staff member
These are ESD protection diodes, not involved in any communication.
But if such diode is burnt, sometime its corresponding data line may be affected too.
 

prodigy83

Member
Does it matter with those diodes which way they go then?
I found a short on PP3V3_UPC1_LDO
Using the thermal camera and injecting voltage, nothing heats up at 2.8v as it only pulls .03 amps.
I would assume this is the corresponding (UF500) CD3215 chip?
 

2informaticos

Administrator
Staff member
Very likely bad UF500.

The protection diode doesn't have dedicated soldering direction.
As per schematic, has two diodes connected back to back inside.
 

prodigy83

Member
Check PMU_ONOFF_L level w/ and w/o audio flex connected.
Also test using SWV012/13 pads instead of power button.
Update, I replaced UF500 and we now have 20v, and amps are pulling too. Still doing the same thing with the power button now working and the recovery boot loop. So I went back to what you said at the beginning of this post and below are my findings.
SWV012/13 with the audio flex connected I get almost nothing, but when I disconnect the audio flex, I get 1.8v. What would cause that? Where should I check next?
 

prodigy83

Member
I do not have continuity on pin 31 for cable 821-03452-01 from one side of the cable to the other side. I am trying to install the OS again now to see if I still get the boot loop in to recovery mode.
 

2informaticos

Administrator
Staff member
"when I disconnect the audio flex, I get 1.8v."
PMU_ONOFF_L is killed by audio board/flex, or touch ID.
Keep audio connected, but disconnect touch ID from audio board.
Let see where the problem is.
 
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