HP 4195A VNA Issues

[outlawpsd]

Having some issues on the VNA side of my 4195A.  Spectrum analyzer side appears fine.  This 4195A lost is config so I'm not sure if its related to that or there is another problem.  I have not read anywhere that this has multiple bands that it has to shift between so looking for a good place to start.  I have read that the DAC (U18 on the A51 board) in the test sets seem to be an issue for more than one person, could this be related to the DAC failing?

[RomDump]

Having some issues on the VNA side of my 4195A.  Spectrum analyzer side appears fine.  This 4195A lost is config so I'm not sure if its related to that or there is another problem.  I have not read anywhere that this has multiple bands that it has to shift between so looking for a good place to start.  I have read that the DAC (U18 on the A51 board) in the test sets seem to be an issue for more than one person, could this be related to the DAC failing?

I think you are talking about the MDAC. This video shows the symptoms and how to repair it, (sorry it is in french so turn on CC with auto translate). As I mention before in your other post, post your message on the hp groups.io group or search the group for 4195A. Someone else already had the same issues you are describing, (I think he also posted a video how he calibrated the 4195A after he repaired it).

[outlawpsd]

Thank you for posting that video, believe it or not it was a big help.  I've looked through the HP.IO groups and downloaded the Python script that has been posted for the calibration procedure but unfortunately, I have never used Python before.  I installed Python but not really sure what to do next - I've got to get up to speed on how to make all that work first.  Plus it looks like there are multiple .py files and there isnt a procedure written on how to use them.  I dont know what needs to be done first, second, etc.  Got a lot to learn.

[outlawpsd]

Just wanted to follow up on the repair of the initial issue that I posed about.  I replaced both A50-U26 and A51-U18 with a Maxim MX7523JN and everything is working now.  I didnt have the tools to figure out if it was on the transmit or receive side so I took a bit of a shotgun approach to it.  Now on to figuring out the cal.