PSPro only boots into Safe Mode

Hi everyone,

i’ve got a PS4Pro Mainboard Modell 1-981-472-21 NVA-001 with a odd kind of error.

On startup the device does a blot on startup, the TV gets a black signal turning its backlight on but no picture. After some seconds the tv backlight turns off again, and the PS4 beeps once. A further seconds later the PS4 shuts itself off.
After this self shutdown the PS4 can’t get startet again. Only if i pull out the plug for some seconds and discharge the condensators by holding a button, the PS4 can be startet again.

What is possible is starting into the safe mode by holding the start button unti two beeps.
In Safe Mode the PS4 runs normal into infinity. But if i want to reinstall the OS, or reset it, the progress bar runs to a certain point, then the screen goes black again, the PS4 shuts itself down after a few seconds, and again can only restartet after draining all power out of it.

The fan is working normal most of the time. In the self shutdown of the PS4 the fan shuts off some seconds in advance.

What i already did is reball and resolder the SIE, which changed nothing about the bahavior of that PS.
Now i have no idea what i can check for to diagnose what is the cause of this error.

Any ideas?
If further info is needet i’m more then happy to provide it.