Diagnosis
Mineral scale or coffee oils have gummed up the pivot mechanism inside the black plastic housing. It's a mechanical, not electrical, issue.
How to Fix It
Clean the pivot. Dampen a cloth with white vinegar or citric acid solution. Work the arm back and forth while wiping all visible metal pivot points. Then, run a vinegar descale cycle to let vinegar steam clean the internal parts. It should loosen after a few minutes of working it.
If That Didn't Work
The internal spring or detent mechanism may be damaged. This requires disassembling the brew basket assembly—not user-serviceable for most. Contact Technivorm for a replacement brew basket unit.
Heads Up
Don't force it. Forcing it can crack the plastic housing or break the detent ball, requiring a full unit replacement.