Today I did some more measurements on the YIG supply buy adding resistors in series of the main coil and the FM coil to measure the current (by measuring the voltage over the resistors).
I believe the signals for both coils are OK which rules out errors on the analogue board.
Since I am unable (due to my instruments) to measure the output of the YIG or any mixer in the gigaherz range I am still not sure if the output of the YIG is too low, causing low signals further down the signal path.
I connected a 10Mhz sine wave signal with 1.2 RMS volt to the SA but the SA shows only several millivolt on the screen. Somewhere the signal gets depreciated.
How canI find where the signal decreases without being able to measure the 2.12 Ghz ??