You definitely should have 24V, or the switches won't work, just check how the attenuator clearly says 24V, if missing it would explain it all.
Once you have the 24V tested working, if the signal keeps failing:
The attenuator block has four elements (-5, -10, -20, -40dB) and makes a combination of them in series and/or bypassed.
If one of them is burned, you'll get an open circuit.
So try finding a signal by manually setting attenuation to -5, -10, -20 and -40dB.
It's pretty easy to disassemble, but there're a lot of screws behind the cover, where the sma connectors are.
This is it:

One 8592 had that one burned, other had a burned transistor array which activated a rf switch, whose coil was completely roasted, can't remember what it was for.
It was a latching switch, so it only needed a small pulse to change, but the switch contact had fallen (Plastic rivets...), so my guessing is the system did not detect it switching and kept energyzing the coil until it overheated, then everything burned down in a chain.