820-00281 starts no boot VCore stays above 1V

[grmacs]

Fan spin and will cycle off and back on without the battery connected.

I tested Out of the mac board only.

corrosion around U5710 (no stuff) pins 13-18 and pad 2 of R7512 is gone there but still get 5V at PP5V_S4 and diode mode/voltages of those SCL/SDA lines seem good.
Corrosion at pin 1 of CA326 so I replaced it. diode check there looks ok and get 12.65V there.

MOst rails present but no PPVCCGT Ph1 or ph2
0Vat LB700: 5VUSBCT_LL

Not sure if the fact that it cycles power once without battery and then stays on is a sign of life or not.

PLT_RST_L is 3.3V and steady.

 

[2informaticos]

VCORE should drop bellow 1V after 5-10s, if really boots.
iGPU voltage doesn't come on until high graphics load is detected.

Possibly other components, or traces damaged by corrosion.
Can also be BIOS issue, try known good one.
Accumulated crap under BGA chips is an option too.