820-00840 dies near end of boot

[Outofwhack]

Immaculate board - no evidence of liquid damage.
ppbus_g3h 13v

With only screen connected, chimes, apple logo appears, then just before time-bar completes screen goes black and repeat.
With only external monitor connected on usb-c same behaviour seen.
Alternate SSD tried same result

Ive tried known good BIOS with clean ME same result.
Current draw with screen attached never goes beyond around 0.3amps before failure.

Wondering where now.

 

[2informaticos]

Try starting in safe mode.
If you can load macOS then, I suspect iGPU failure.

 

[Outofwhack]

No I couldn't load macOS in safe mode either.
I measure 0volts on PVCCGT_S0G_PH1/2/3. Each approx 1.8ohm to ground.
pp5v_s0 is 5v
ppbus_g3h_cpu is 13v
Could this cause my problem or is it only switched on at a late stage?

 

[2informaticos]

iGPU doesn't get power until high graphics load is detected.
Not sure the correct resistance to ground on iGPU core; compare with good board.

 

[Outofwhack]

Yes the 1.8ohm to ground is consistent with other boards so that cant explain stopping before end of time bar.

 

[2informaticos]

Check if you can load Linux, or Windows.

 

[Outofwhack]

Ha! Ive been trying to install Linux on another Mac all week! Ive tried creating a bootable USB stick via a ew different utilities off an ISO and it is never seen when I hold ALT. How can a bootable usb be made? Im using an ISO of opensuse.

I dont have a windows distribution but I do have a Microsoft repair usb which holding ALT does see.
Result is I get a windows logo but then a blue screen reporting mishandled exception and goes back to the macOS logo, rinse, repeat.

FYI Boot holding d I get a report that there may be a problem with the SMC with reference code PPF003 and PPN001 so I decided to try my first SMC removal, reball, replacement with one from a liquid damaged board. Sadly no change [for a lot of time kicking balls into holes - think I will try paste next time].

 

[2informaticos]

In regards of your errors, try known good trackpad flex/board.

 

[Outofwhack]

Aren't those ruled out? Ive got the logic board connected to the screen only for the most of this. However the results are the same with trackpad and flex connected. But I will find alternative trackpad and flex if you think so.

 

[2informaticos]

However, your basic problem shouldn't be related with these errors.
I suspect CPU in this case...

 

[Outofwhack]

If the CPU is dead what displayed the apple logo and increased the time bar? Surely that is driven by the CPU isn't it?

 

[2informaticos]

I didn't say DEAD CPU!!!
Very likely iGPU problem; which is of course embedded into CPU.