Pixracer (R12) and/or ACPS4 fail


After remodeling my quadrocopter, I got the following error message: the buzzer beeped every second.

After powering up ACSP4 and Pixracer alone, it was quiet.
If I have a consumer, e.g. connected an ESC. Again the annoying beeping.
The Piexracer is also silent on the USB port.

I do not know what to do. Is dr Pixracer defective, or the ACSP4?
How can I test that exactly.

Many greetings