8563EC spectrum analyzer amplitude problems, no codes, odd cal

[NickyDoes]

Hello,

I came upon an Agilent 8563EC 26.5 GHz spectrum analyzer. I'm getting into RF, but am not experienced at this point - and don't have much in the way of cables, adapters, let alone synthesizers. I do have an older HP 1.8 GHz analyzer that works great, so I can check some things. I checked the attenuator, for example. The attenuator appears to work well.

This SA is failing in ways unknown to me. I've read through the service manual, and could do quite a few of the checks - but would appreciate a bit of guidance in the rationale of what to check and what just doesn't make sense to try.

I attached photos rather than describe all the situations. I get normal looking spectra with excessive amplitude when measuring the Cal output with a span under 1.8 MHz. At and above 1.8 MHz, the measured amplitude moves to saturation. I realize there's a mode switch at 1.8 MHz, but I'm not yet grasping the fundamentals of what is going on.