HP 8591a spectrum analyzer problem

[kc8ard]

I can post some pictures later tonight, but last night when I turned on my spectrum analyzer I found a wall of junk from 9khz to about 7.5mhz. past 7.5mhz, the SA operates normally. The noise floor is normal, but when I tune up and down from about 1mhz to 7.5mhz, the noise will come and go. It's not really broadband noise, but a series of peaks that look like garbage. It's strange and I have no idea where to start looking, though I'm pouring over the service manual now.

[kc8ard]

Here are the pictures.  The last thing I did was just look at the vswr of a alpha delta 40m dipole through a minicircuits zfdc-20-5+ directional coupler.

[Marcel G]

Mixer damage.

See my post and pictures about the Advantest R3131 Spectrum Analyzer (last pages).

[kc8ard]

Mixer damage.

See my post and pictures about the Advantest R3131 Spectrum Analyzer (last pages).

That's my first thought, that it's the A4 first converter board.  It's the first signal path, past the attenuator, starting with a 1.8ghz low pass filter section.  Luckily, I found a board pretty cheap on fleapay.  If it's not the problem, i'll just have a spare board.The weird part about all of this is that it passes both the conf test and all cal tests. If i inject a signal anywhere within that range, it shows cleanly, but, the spurs are still there. I'll have to tear the board out and look at it when I get the chance. It looks like there is a ton of work(and screws) just to get to the section.

  One of my thoughts is that it could be the reference pll, contained within the a25 counterlock board, as it outputs a 7.5mhz reference. My problem abruptly stops at 7.5mhz, and all of the spurs occur on both sides of the reference signal.

[Aleksa]

Did you find out what the problem is? I have the exact same problem. Mine doesn't go through self cal, always fails. The cal output signal is -32db(so it says, don't have a way to confirm it).

[Henrycarra]

Hi KC, did you finally repaired the HP8591A/ What was the problem
I have one with the same noise below 7.5MHz
Thanks for your time, Henrycarra