820-3115 wont load OS

[No-Clean]

Clean board, OS tries to load, Apple logo shows on screen then a second later the forbidden sign comes up.

All test have been done with ONLY the screen and keyboard connected.

Tried working 10.11 and 10.13 from USB external OS
Tried clean BIOS
Tried different RAM chips

But no luck.

 

[2informaticos]

The machine works with USB macOS?
Test it disconnecting internal HDD.
Also test with one good RAM module at time; may not work with PC3-8500.

Run EFI ASD, w/ and w/o internal HDD connected.

 

[No-Clean]

The behavior is the same with internal HD or with USB macOS, all test with USB were done with everything disconnected except screen and keyboard.
Different RAM one at a time already tried, will try ASD tomorrow.

Thanks!

 

[No-Clean]

Tried different RAM all different clock speeds one at a time.
Tried EFI and OS ASD but it doesn't even start, comes up with all kinds of errors.
Stuck...

 

[No-Clean]

Attached are both errors showing on screen for both EFI and OS ASD.

 

[2informaticos]

Disconnect internal HDD, before starting ASD.

 

[No-Clean]

Tried that, same errors come up, also tried disconnecting other components one by one but no luck.

 

[2informaticos]

Try heating PCH and/or CPU with good flux applied.

 

[No-Clean]

Just did, good quality flux and to make sure I ran it via the rebelling machine with a lower temp profile, but same behavior, I guess this is the end of this one...

Thanks !