Probably because of temperature changes in VEAs and TCS being down earlier, I've had to add two new PI filters. The modes at 18040 (now 18037.5) and 18056 (now 18055) hz have moved down in frequency and were both ringing up and breaking the lock. First attached plot shows some detail of the bandpasses. The dashed lines are the new filters. Second plot shows the spectra of the new modes, the vertical red lines are the troublemakers, the green trace is from a lock when they were both high, red trace is live.
Except that the blue filter doesn't seem to be working... I just lost lock again.
I can't seem to do anything about the 18037.5 mode. None of the tweaks (gains, phases) do anything when the mode rings up. I've also tried sitting at DC readout for an extended period to see if that helps quiet the mode any, but I'm not having any luck.
The issue was fixed by setting the PLL set frequencies to match the new band pass filters. Did this for both MODE27 and 28. This PLL thing was buried in the "If PI seems unresponsive" section of the instruction so I broke step 3 into two parts.
Thanks; this was absolutely the right steps to take when there's large temperature/TCS changes. Apologies that the need to change PLL frequency wasn't obvious in the wiki. Thanks Nutsinee for editing that!
Also, feel free to still call me at anytime (even middle of the night), especially if PI causes more than one lockloss. My number is on the main whiteboard.