The squeezer did not engage when we got to NLN tonight. The 79.4MHz VCO was locking to 79.2MHz, and the guardian told us to adjust TUNE OFS. We disabled the servo and moved the slider to 79,4MHz. We could not enable the frequency servo without it driving back down to 79.2MHz. We tried to continue locking with the servo disabled and manually setting to 79.4, however, SQZ OPO guardian is now saying it "can't lock the OPO, check pump light on SQZT6". We are unsure what is going on.
The solution to this issue was to ensure that the "Ramp Enable" switch in the TTFSS servo page was switched to "off".
I think this is the same issue as Friday night when TTFSS seemed to have jumped straight to "Acquire" without engaging the loop. The 79MHz message came up because when TTFSS was unlocked and the SQZ laser was not following the IMC VCO (the SQZ laser needs to follow the main IFO laser for the squeeze angle loop to close, the 3MHz one). The whole guardian automation was written assuming that TTFSS works reliably enough and it doesn't touch any of these TTFSS channels. TTFSS is all Beckhoff controlled.
Found myself stuck with this error tonight as well. Don't know how exactly I solved it but it seemed to be a combination of switching the error signal on the Slow frequency servo to "On" and possibly waiting at "Adjust Frequency" state for the SQZ_LO_LR guardian.