J. Kissel, S. Dwyer, D. Barker, J. Driggers, E. Hall

Some of the way through recovery (there will be a LONG aLOG to come; we're not yet fully covered), but we changed some hardware and the source of the problem hasn't been aLOGged yet, so I wanted to get this one in there separately. 

Here's the story:
- We get to ALS COMM and DIFF steps up the lock acquisition sequence. Part of the automated sequence is to search for the right COMM and DIFF VCO frequency for IR resonance.
- This process failed, because the channels used to track the VCO frequency, H1:ALS-C_COMM_VCO_FREQUENCY and H1:ALS-C_DIFF_VCO_FREQUENCY, were dead, reading identically zero.
- These channels are copies of channels produced by the timing fanout / timing comparator system, H1:SYS-TIMING_C_FO_A_PORT_11_SLAVE_CFC_FREQUENCY_1 and H1:SYS-TIMING_C_FO_A_PORT_11_SLAVE_CFC_FREQUENCY_2, which are renamed by the ALS Beckhoff code to something more human readable. 
- Note the "PORT_11" part of the fanout / comparator channel name. This represents the port number of the timing fanout from which the comparator gets its timing reference. The ALS Beckhoff code, which is common to both observatories, has the PORT 11 hard-coded into it's PLC to define the channel renaming.
- After calling Dave, we found out that the timing comparator's reference signal had been moved from port 11 (12 on the front panel of the chassis) to port 15 (16 on the front panel) when the new 9.1 MHz oscillator was installed this morning. The new 9.1 MHz oscillator's reference was put in PORT 11. Because the port user changed from a comparator to a RF source, the timing fanout / comparator's channels and infrastructure totally changed, not to mention the signal that now populates those channels.
- We looked at LLO's timing MEDM screens to see that unlike LHO, they've left the timing comparator plugged into PORT 11, and stacked additional RF sources beyond it, instead of what was intended this morning, which was to keep all the RF sources together, and push the comparator off to the end. Again, because this is hard-coded into the Beckhoff PLC, and changing the PLC and rebooting the Beckhoff system ALWAYS causes more problems than its worth, we elected to revert the timing cables.
- We've moved the comparator's fiber back to PORT 11 (port 12 on the front panel), and put the 9.1 MHz into PORT 12 (port 13 on the front panel).
- It took some clicking of theses port numbers on the MEDM screen for the comparator and the 9.1 MHz to show all green (indeed, the 9.1 MHz took a little bit longer, because the OXCO had to resync, but it had been syncing all day, so it only took ~10 seconds).
- Once the comparator signal was restored, the ALS channels made sense again, and we instantly moved past that step in the lock acquisition sequence.

Lesson learned? 
- Everything depends on something else, and every change you make to the IFO matters, even if you don't think it does. 
- Please aLOG everything you do. EVERYTHING. Granted, even if you had, we probably wouldn't have put two and two together until calling Dave, but still. If we've changed the 9.1 MHz frequency reference, the main RF source for locking the IFO, it should be in the aLOG.