This is my first post to the group, so hello everyone.? You've been a great resource when I've needed to search for information on prospective or actual TE purchases; thanks :)

I recently acquired an Agilent 4396B spectrum/network/impedance analyzer with all of the options (1D5 oven, 1D6 time-gated measurements, 010 impedance measurement) in non-working condition.? The main problem was some stressed SMD electrolytics on the A50 DC-DC converter board, as discussed in service bulletin 11.? There is also something odd in the source assembly, but it seems to be after the ALC power detector; current theory is the semi-rigid coax link from the output attenuator to the bulkhead N connector, or perhaps the N connector itself.? I'm documenting the repair here:



Looking ahead I have a few questions (and will undoubtedly have more as I dig into the analyzer's capabilities):

1) The calibration constants are stored in an EEPROM and updated over GPIB, but as far as I can tell the actual commands and format of the data are not documented.? The only approved way to update the calibration is to use an HP-UX program called "ADJ4396B" running on an ancient HP controller.? Is this likely to be a problem in the long run?? Should I consider sending the instrument out for calibration (assuming the cal lab even has access to this magic software)?? This is for home / hobby use only, so it likely doesn't matter, but I wonder if a window of opportunity is closing as these units get older and the last support is dropped.

2) Has anyone actually laid eyes (or camera) on the insides of the 43961A impedance test fixture?? I have no need for it except curiosity, but it would be fun to leverage the 010 software in my unit.? It could probably be a worthwhile learning experience to build something equivalent at lower frequencies.

3) Not a 4396B question per se, but what is the currently recommended GPIB interface solution in 2019?? I would prefer not to use any NI stuff or the VISA library, but if that's the price for being able to run useful third-party software (like KE5FX's phase-noise tool), I will.? Although in that case I would still prefer options which *can* work with the VISA library but can also work without them.? Cross-platform compatibility with Linux and Windows would be a plus.

Regards,
Mark

2) nope. But I was told that it uses some kind of transformer, so the block diagram in the service manual is deceptive. I furthermore heard RUMORS of the one for the 4195A working on the 4953A if you slinked around with the cables. Sadly, this is all I know - so far, all managed to elude me.

Yes, I believe the general shape of the circuit is known or can be deduced from available literature.? The best summary I have found is here:
? ?(about the 4291A RF impedance analyzer---similar vintage from the same design group in Japan)
But it would be nice to see the innards.? The difficult aspects will be those which cannot be represented in a schematic diagram.

I have opened the 41951A impedance test kit a while ago to see how it was constructed. But there is really nothing fancy inside. Some inductors, a few caps...
I uploaded the pictures if anyone is interested.





Of course these pictures are useless to draw a schematic from it. If better pictures required, I will open the box again. Doing so the first time was quite a hassle because the screws where glued in and extremely hard to loosen.