R&S CRTU-RU/CMU200 front end troubleshooting

[winofi]

Hey there,
today I started to dig into the front end board of my CRTU-RU. It showed slightly off power levels for ever and has the external loop test failing for some frequencies by just a few dB.

Recently I tried to use the build in signal generator at lower frequencies and noticed that the sine is clipped for frequencies (not exactly) <10MHz (see images). The clipping occurs on all three outputs for high power levels. For low levels or high frequencies the signal looks fine. So my hope was that there is just a broken power rail causing clipping.

After opening the CRTU and tracing the signals I found the issue in the G4C labeled switches. Following the markings they seem to be UPG2179TB ones. Looking at the datasheet they seem to be straight forward 3V SPDT RF switches.

Now it gets interesting. All the switches seem to work fine. The signals get routed as expected when changing the output configuration. The datasheet specifies positive voltages to operate the switches but in my device -4.9V are applied to the switches to control them. They seem to work fine with this voltage and the front end self test is happy but the ones after the first amplifier stages of the TX signal seem to clip for high amplitudes (see images, the show the output signals but the waveform is the same directly after the switches). This is true for both TX paths.

So my questions are:
Do the switches normally work with -4.9V and are broken? Why do two of them break at the same time (both TX paths).
Or is the voltage wrong (broken power rail?) and the switches do crazy things on -5V?

One thing I also noticed is that the datasheet specifies the outputs require external dc blocking, but there are no dc blockers between those switches (wrong switch datasheet?). I also can not measure any dc leaking out of them.

All the botches on the front end picture are factory defaults. The only think I every repaired on the CRTU was an oscillating power regulator in the reference board.

Any thoughts and hints are welcome. Thanks in advance.