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?

 

[sekidata]

Yes, the source machine is showing the lightning bolt and the USB logo. The host is set to Show All Devices in Disk Utility. The connection between the two devices is good because I just ran another DFU Restore.

 

[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.