those little tones at -70dbc should not exist. they seem to be about 20khz apart and not harmonically related to the 1MHz input. Either the 3325a or 3585a still has a problem.
Yes, you are correct. When I use an analog oscillator as my signal source, those spurious signals disappear, so the problem isn’t in the 3585A. I am aware of this situation, it is a problem in the fractional-N PLL circuit on my 3325A. That repair may be coming up in a future video.
Gotta love these fairly simple repairs. Many of these sub-assemblies contain custom HP unobtanium parts that can only be acquired from a doner unit. I have several units that I have simply replaced the entire sub-assembly because I didn't have the test gear to properly troubleshoot the issue. I'd love to get my hands on a 3585A eventually.
