820-02020-A Liquid damage and power cycling

GfilipeZ

New member
Hi,

This is my first M1. I feel a little lost and not knowing where to start.

The machine had a liquid damage, next to UC300; UC710; JR940 and UP900.
I did reflow to the IC's. In the measurements I didn't find any low resistance value (short circuit) and the IC's output voltages are correct.

With the battery disconnected, the machine is in a loop. The chime is heard, it reaches 20.3V for 1 second and returns to 5V again.

With the battery connected, it also loops. But after restarting 6 times, it apparently ends up booting (it always remains in 20.3V during de loops, doesn't fall to 5V). But only the desktop image and the mouse appear. The icon user does not appear, not even to enter the password.

Most likely I will have a short circuit, which I am not able to identify.
 

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2informaticos

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

A short circuit should prevent the board to turn on.

Try to put the machine in DFU mode.
If there is important data, do Revive; not Restore, which will erase SSD.
 

GfilipeZ

New member
Hi @2informaticos,

Thank you, for your reply.
I tried the revive, but still the same.


I've been thinking a little more about this problem and analyzing the schematic. In practice the conclusion I came to is that the external monitor is being identified as a secondary monitor. That's why, only the desktop image appears, and the user icon does not appear.


From what I understood from the schematic, the display is identified by the signal LPDP_INT_HPD. That goes directly to the U0600 processor. I have already removed the connector JP600, in case there is any corrosion. I checked the voltage of this signal, and it is approximately zero.

How is it possible for the machine to continue to identify the external monitor as secondary? Even if there is no voltage present at LPDP_INT_HPD?
Do M1 work differently from Intel?

Could it be a processor malfunction?
OS restore will be my last solution as the customer wants to recover the data.
 

2informaticos

Administrator
Staff member
If no internal LCD detected, you should get welcome screen on external monitor.
Really strange to get the desktop before logging into macOS.

Can you access Internet Recovery on external monitor?
Try to save the data puting the machine in Target Disk mode.
 
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