The MC WFS have apparently been bad for a few days, causing the MC alignment to drift away at DC. We tried a few things to fix it, including jiggling some EPICS settings in the WFS head & demod screens. This seemed to work for WFS1 but not WFS2. Confused, we decided to go stare at the rack 1Y2. While doing that, we noticed that the top two Sorensens in 1Y1 (these are directly below the Guralp box) were at different voltages from nominal. The 5V had dropped to 4.2V and the 24V was at 24.6V. We adjusted the knobs until these were set correctly. After this, the MC WFS appear to work again.
When working in a rack, you must be as careful about accidentally touching things as when working on an optical table.