iPhone 4 turns off after few minutes (liquid, logicboard)

Hello,

I got a iPhone with all markers red and repaired everything there (was really a lot of things). Connectors were full of patina (battery, LB) ...

Now it turns on and works, but I have a few Problems with it:

1. It is a Jailbroken pre iOS 7 (I think it is iOS 6) device and the settings crash once I start them. A week ago they suddenly worked, now again they don't. Thus I can't access WiFi or other things. Cydia isn't installed, Appstore won't start because of no internet connection (SIM-lock as well)

2. After some minutes (it seems like it is more or less always the same time) it turns off. Since it has a 3rd party LCD you can see how it is fading out.

I put that LB in another iPhone and the error persists.

EDIT: After a few hours in a isoprop bath error remains. Cleaned patina even below shields