Andrew switched out the bypass capacitors to ceramic ones over break. Now all of the channels are functional, so I guess that was the problem (I don't know what the physical problem would have been before, though).
Here are some measurements of the frequency response.
Here's the noise. I don't know why it has the "edges", I'm pretty sure I made the measurements the same way as I was doing before and used the same stiching script... I might repeat these measurements later, but it's at least an idea.
Channel 1 has much higher noise. Possibly because there are power lines that cross over the area, whereas for 2 and 3 the power lines are routed from the side? Could be another reason though...
Data and scripts attached.
%another plotting script
%sorry the numbering is all out of order
%1-2 mag and phase channel 2
%3 - phase channel 3
%4 - phase channel 1
%5 - mag channel 1
%6 - mag channel 3
%7-10 noise channel 3
%11-14 noise channel 2
%15-18 noise channel 1
%% This is a module for stiching spans of overlapping PSDs of different frequency bin size from SR785
% Assuming a logerithmic scale of frequency, it is desirable to
% stich the smaller frequecy ranges to the bottom of the larger ones
% wilst truncating out bins in the larger span.
%Feed in frequency matrix f(n,m) with correesponding floating point
% [freqStitch,dataStitch] = freqStitch(freqPoints,dataPoints)