Hello to everyone. First and foremost, I am new to all things RF. I am not new to electronics (AC/DC circuitry). I have just acquired a HP8566B Spectrum analyzer, in hopes of repairing it to specification. I have access to all repair manuals related to this instrument, and have read much of them. (Not all). I purchased this analyzer in pieces and stages Display from one seller, RF section from another, and interconnect cables from yet another source. Initially I had a bus connection issue, easily resolved. Then I did a scratch and sniff, all appeared viable, so I powered up, current limited and monitored. All ok. Display however shows what I interpret as noise in the low frequency band. Upon investigation of the front end, so far, is no signal throughput. I have only a tinySA spectrum analyzer at the moment to produce signal to ~6GHz, but also no signal through in the .100Hz-2.5GHz using my arb gen at any amplitude. Low signal is no connection through the low/high range switch. (replacement on the way)This leads me to believe possible over voltage applied to front end. What I need to figure out however, is whether the linear noise slope I see on the display can somehow have something to do with it, and where I may need to investigate. I have no way to characterize response from any components at frequencies >80MHz as I can only produce, or measure at once, not both. Hoping someone more experienced than I can see what I see and go,"I've seen that before, it's the (insert obvious answer here)" Again I am new to RF equipment, but not totally clueless.