I put the gyro back into the normal configuration today. It is now locking in both directions again. The bandwidth seems slightly improved, as I didn't have to be quite as careful when working on the table to keep it from dropping, but it is far from good, and the 200kHz+ oscillation still shows up with enough gain. I had set up the PLL but was having problems locking it when I had to leave.
A couple changes:
I took some time to label nearly all of the cables we work with at the controls interface. The REFL PD signals, the CW & CCW error signals, the PZT and AOM VCO control signals, the TRANS DC signal, the SWEEP drive from the function generator, and two cables going to dedicated DAQ channels have all been labeled. This way we don't have to tug on cables or follow them across the table to figure out what is what. We should be prudent that we don't change them around without relabeling them appropriately
Tomorrow morning I'm going to figure out what's wrong with the PLL, then lock it and take a spectrum to see if things have gotten better with the new PD, new modulation frequency, and fresh realignment. Then I plan to take a bunch of transfer functions to try and diagnose our loop problem. Specifically:
(2) is necessary to obtain the OLTF of the loops from (1), as we will be using the SWEEP input for the excitation, and the TF from SWEEP to OUT is not the same as that from IN to OUT.