A1286 2012 820-3330 Very slow, fan spins normally

[VinceLx]

Hello,
I have this board which had originally a short on PP3V42_G3H. I injected 3.4V on L6995, put alcohol everywhere and found an issue with U6400. For the moment I only removed L6400, I don't have a spare to replace U6400 yet.
Now the board boots, internal display is ok, but very very slow to boot and to work. No battery installed. Activity monitor shows 89% used by the system.
In safe mode: same story, even more slow if possible, Activity monitor shows 95% used by the system.
PRAM reset: no changes
ASD OS: Passed
ASD EFI: Passed
I am almost sure that at a given moment with some SSD I saw kernel_task above 600%, but I am not able to reproduce that.
Hardware monitor: does not show high temperatures, fan is always around 2000rpm
I swapped memory, SSD, same story.
What could I do next?

 

[Narek]

I’m guessing it behaves like this because of no battery. I had similar cases. Connect good battery and check again.

 

[VinceLx]

I tried your solution just to be sure, and... it worked!
I don't understand. I am now in front of another good working 820-3330, same conditions without battery, and Activity monitor shows system use 1%!
Why?

 

[2informaticos]

Is classic issue for 3330 board...

 

[VinceLx]

Ok... no way to solve this? It works fine with battery, so that's all?

 

[2informaticos]

Yes, needs to have GOOD battery.
Crap chinese battery will not fix the problem.

 

[VinceLx]

Ok, thank you both for your help.

 

[VinceLx]

An update on this: installing Catalina updated the Boot ROM version from MBP91.00D7.B00 to 233.0.0.0.0 (with battery), and now I can remove the battery and the board works normally. In case in helps someone