820-01598 A2159 with startup issues

[sekidata]

This 2019 Pro behaves in a way I have not seen before. It initially started up to a circle with a line through it. I performed a DFU Restore, which completed successfully (padlock). Now, when I startup using Internet Recovery, the machine gets part way through startup, then the fan blows hard for an instant and it shuts down. I'm looking for a logic board hardware issue but haven't found anything. Identical behavior when installed in a different topcase. Passes the Apple Diagnostics test with "no issues found".

 

[sekidata]

The only other observations are that the original topcase had a malfunctioning Touch Bar (all pixels illuminated simultaneously in one bright bar), the trackpad was not clicking, and the keyboard was non-responsive.

 

[2informaticos]

Can you start in target disk mode?
If yes, check if SSD is good.

 

[sekidata]

In target disk mode, I get no drive mounted on the host computer. Bad SSD? I have PP2V5_NAND_SSD0 at 2.5V.

 

[2informaticos]

Do you get the USB logo on the screen?
Did you select "Show all devices" in Disk Utility?

 

[2informaticos]

You can try replacing the NANDs...

 

[sekidata]

I replaced both NAND modules with ones from a donor board, but the exact same symptom persists: spontaneous shutdown during the first 10-20% of the startup progress bar. DFU Restore successful. Apple Diagnostics shows "no issues".

Any other ideas?

 

[2informaticos]

Probably CPU issue...

 

[sekidata]

I think you're right. I tried running Internet Recovery with Verbose Mode on several times and it always crashes on the CPU test.