Uehara, Enomoto, Ge, Yamamoto with remote help from Miyoki-san,

Today, we unintentionally tripped a circuit breaker which was for the MCF-PR area.

After consulting with Miyoki-san over the phone, we maganed to recover it.

Be mindful that the IOO and ALS racks are running at very close to the current limit of the circuit breaker.

We are thinking of switching to a different AC source for the ALS racks in order to improve the situation once we figure out how much current are used at various AC sources.

[Some details]

The circuit breaker tripped when I switched on one additional RF source (N5181B) that was mounted in the ALS0 rack.

Consequently this shut down the following electronics:

• All the circuits that run with +/-24V source in the IOO0, IOO1, ALS0, ALS1, PRM and PR3 racks.
• All the electronic equipments (ethernet router, oscillators and Kepco units) that are supplied with AC power in the IOO, IOO1, ALS0 and ALS1 racks.
• The PMC and FSS boards in the PSL which also run with +/-24V.
• We didn't check the optical lever SLEDs, some of which might have been also shut off.

Within a minute or two after the incident, we intentionally switched off two Kepco units supplying +/-18V in the computer room in order to reduce the chance of damaging the common mode servo boards.

Calling Miyoki-san, we determined that the circuit breaker belonging to the SC-3 electricity distribution board nearby the PSL room had tripped. The AC source for this was the one labeled as "MCF, PR konsento". We first switched it to the off position and then toggled it back to the on position. At this point, the AC power successfully came back while we kept both pairs of Kepco units switched off (the ones below the IOO0 rack and the computer room). Subsequently we switched on both pairs of the Kepco units simultaneously.

Yamamoto-kun then restarted the relevant front end models because they had stopped running due to the IO chassis invisible to them. After all these above have been done, we confirmed that the PMC, FSS and IMC lock without an issue except that the IMC transmission was found to be as low as 0.1 for some reason. We then touched up the IMC suspensions to steer them back to the optical lever values, but while this improved the IMMT1 trans QPD readout, the transmission didn't increase much. We realigned the IMC input pzts, which brought the IMC trans back to 0.3 which is still too low even if considering the fact that one of two paths in each MZ interferometer is blocked.

Despite this effort, we think that the alignment of the IMC input PZTs is still suboptimal. This probably needs some touch-up by an expert.