Hi Timo,
A couple of questions:
What is the board revision?
What version of firmware?
Does the receiver work (decoding the FT8 signals)?
My first thought is that a capacitor is open or short in the PA's output stages. There could also be an issue with the voltage doubler circuit (D7, D8, D9) that is shorting the output.
Verify the cables and test setup to ensure you do not have a test instrument (dummy load) failure.
73
Evan
AC9TU
