No Connection to Carrier from Pinephone 3G Model

[merlin]

I got my Pinephone 3G Ram Model and can't get a mobile connection.
The Signal strength is always at 0.

The same SIM Card is working without problems on my old Braveheart edition.

I Tested multiple distros, some could read out the carrier name but all have 0 Signal.
Also factory test says "Not Registered" and signal strength of -90db.


Could my modem be broken?

Currently postmarketos is installed.
How to debug this?

Thank you.