820-00850 MacBook Pro A1989 2018 with possible CPU damage?

[sekidata]

This board came in with extensive liquid damage in the USB-C, backlight, and ISL9240 areas. After clean-up I replaced ISL9240 and a few other corroded components. PPBUS was shorted to ground and I found U7210, one of the CPU power chips, shorted; replacing it removed the short on PPBUS_HS_CPU.

Now, I get 20V on USB-C drawing 0.51A, PPBUS is 12.6V, and I have SSD and G3S rails. But no startup. DFU Restore proceeded to the padlock symbol, but the target computer showed no signs of life other than trackpad clicking.

What’s the best way to troubleshoot whether the short on PPBUS_HS_CPU has damaged the CPU, before I spend a lot of time fixing other issues on this board such as LCD backlight?

 

[2informaticos]

Very likely dead CPU; overvoltage from PPBUS_G3H destroyed it.
Compare ohm resistance to ground on the CPU coils with good board.

 

[sekidata]

The resistances on the CPU coils match a good board pretty well (3-4 Ω), that's why I haven't given up on this board. I also get 0.9V on PPVCC_S0_CPU, similar to the 0.8V on a good board.

 

[2informaticos]

Failing CPU power supplies many times end with dead CPU.
Even no short on its coils, doesn't mean CPU has survived.
After 10-15s, core voltage should drop from 0.8V; compare its behavior in time with good board.

There is no reason to go for backlight, if no USB activity, nor image at least.

 

[sekidata]

Yes, I see a drop in Vcore on a good board after 10s, but not on this board. Ok, goodbye CPU.