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Hi folks,

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my 8510C system recently developped an unlock error, so I have checked the source HP83651A first.

It turns out, that the source output below 2,4GHz is exactly (to the Hz) 100MHz too low, while above 2,4GHz it is spot on.

Also, the 8510C works fine above 2,4GHz.

Has ever anybody seen such a strange problem? Any ideas what could cause this?

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Tom

Hi Tom,

I got same problem few years ago on my 83630B. The faulty module is the low band module on the RF deck at the far end opposite to the output RF connector.

Many thanks for your feedback! What was the problem with yours? A broken data line? Why exactly 100MHz shift?

Or is some YIG lookup table messed up so it locks to the wrong harmonic? How did you get it fixed?

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Tom DG8SAQ

I was only changing the low band module, because I got one from an other older generator. In the 8360 families, this low band module is the weak part. That's a very complicated part, I was trying to obtain solutions to know better how it is made inside to open and verify it but it seems it's very difficult to have some information. At the present moment, having got at least 7 different generators from this family, I already have in a corner 2 low band modules with problems. That's why I try to collect all generators from this family because we need so many parts to let them alive. That's the most recent family that we can repair and calibrate ourself without help of unobtainium software or hardware. Later products are PSG and nothing is possible without requiring Keysight services. From memory only, it was in beginning of 2018 that I was swapping this module. Once the swap made, the error disappeared, and few months later i already sold the 83630B because having replaced it with a 83640A. In this last one I replaced the VFD screen that was extremely dim. And I currently search to increase also the output power and to add an output attenuator. I don't remember what was the error on the second low band module that I needed to replace too, also for an 83630B.

There is some information on the low band module A24 in here starting page 36:

I see now that this is a microcircuit and not repairable.

I suppose, in my low band module the oscillator has drifted over time such that it locks now to the wrong 100MHz harmonic.

A pitty, one would just have to re-tune the oscillator if it was possible.

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Does anybody know where I could obtain a replacement for the broken A24 low band module of my 83651A?

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Tom DG8SAQ