HP 8753ES Phase Lock & Source Issues

[cyma]

I recently purchased an HP 8753ES network analyzer.  What I failed to realize is that the seller had combined 3-4 bad units into a single one and given all of the problems to me.  I can deal with some of these (bad port coupler, bad switch) but I'm struggling on two of them.  One is a sampler (A6) which nominally works but is 20 dB down.  The other is the source which fails to allow the machine to do a phase lock (A3).

I'm pretty sure that some part of the source is bad, in part because the person who put this machine together kindly labeled all of the failed components.

Symptoms:
1)  The S11 is erratic below 1.2 GHz and between 2.7 and 3 GHz.  Otherwise it tends to be reasonably stable(ish).

2)  When I replace the phase lock board (A11) from another working unit, I see the same results, but the erratic behavior from 2.7-3 GHz disappears.
3)  When I replace the source (A3) with a source  from a 3 GHz unit, it creates other problems, but the erratic behavior from 0-3 GHz disappears.


I get a variety of error messages at various times as shown below:





I have taken the cover off of the 08763-60146 and checked that the connections between the various boards work.  They seem to all be okay.  I am really at a loss as to how I should troubleshoot this.  It seems apparent that something is wrong with the source (A3) but that it may not be completely dead as we are getting (at least nominally) return loss measurements at most of the frequencies.  Looking for suggestions of what I should try or how I can better diagnose this issue.

I have looked into a new source, but these things run 3.5K and that's not quite what I had in mind.

By the way, the port coupler was not only blown, the connection going into the device was completely melted and shorted inside of the tube.  I have never seen anything like this.  There must have been some serious power going into this device.