HP8753E VNA repair

[cyma]

I have an HP 8753E that I’m trying to fix.

I noted that I was getting a very poor response from port B prior to calibration.  Upon disassembly I determined that there had been ESD damage to the coupler and the ~265 ohm film resistor inside was fried.  I replaced this with a 270 ohm resistor using instruction I found online.  After the replacement, the performance improved somewhat but it is still problematic.
I tried swapping the port couplers and the samplers, but regardless of the changes the problem stays on port B.  My next suspicion is the solid state switch (A24 - HP 5086-7539). 

Is there any way to easily test this?  Is it possible and/or likely that ESD damage coming into port B would also knock out the switch behind it (which evidently is static sensitive)?  Is there any way to repair the guts of this switch or is this a lost cause?  Thanks for any insight you can provide.

Images:
Port B before fixing resistor
Port B after fixing resistor
Port B with a different (probably good) port coupler
Port A (working fine for reference).

[KE5FX]

The repetitive nature of the artifact is interesting.  Its period is long enough to suggest that the fault is not actually at the coupler, maybe as much as a foot or so away.  Do you have the time-domain option?  If so, switch to that and see what it tells you.

[cyma]

I did a lot of probing removing various cables along the line and came to the conclusion that the frequency of this only changed when I played with the cable between the coupler and the switch.  This seems to be an artifact of the switch coupling to the coupler.  I have tried 3 couplers and I know that's not the issue, so I'm leaning more and more towards the switch as the cause of the issue.

[cyma]

Additional analysis showed that it was indeed the switch that was bad.  The problem and solution is well described herehttps://www.mattmillman.com/agilent-8753es-repair-part-2/#comment-103920.  I will include a few photos of my repair below for anyone interested.  Bottom line:  ESD damage on port B [2].  This was clear by connecting port 1 to port 2 and then measuring S21 and S12.  One was fine and the other was more than 10 dB off.  So I took apart the switch and noted ESD damage to a diode near the input.  I tested the DC resistance between the switch inputs and ground and also noted that on the good side it was about 3.6 ohms and on the bad side it was about 1 ohm.  I removed the diode (that was shorted) and the switch started working normally again.  These diodes are kind of microscopic, so I used a microscope during the process.  Ideally, I'd like to replace that diode with a similar one.  If anyone knows what diode was used there or the specifications, I'd really appreciate some insight.