[Nakagaki, Ikeda, YamaT]

We could solve the issue of missing PCIe card by replacing DAC#2.
After then ADC and DAC noise were measured for all channels and finally k1iy0 came back online.

Note that PEM speaker output cable is now unplugged from AI chassis because timing synchronization cannot be recovered with plugging speaker.
Please connect it when it'll be used.
According to experience on MCF, after the timing synchronization is established once, it can be connected.
But it sometimes makes an OS hang-up, so it's better to be unplugged again after using.

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Solving missed PCIe card issue
Today, we tried to reproducibility of yesterday's situation at first by removing BO card and then swapping DAC#0 and DAC#1. But OS couldn't find the DAC#1. So we concluded that removing BO card is not an ensured way to operate two DACs. Next, we replaced DAC#1 from S1809372 to S2516731. Then, two DACs could be operated even if BO card was also installed and reproducibility was also verified by power cycles in several times. We haven't identified a reason why S1809372 didn't work properly. But we doubt two cases now and will check them on the test bench.
1. That DAC was just damaged by the issue of speaker.
2. LIGO firmware wasn't applied to that DAC. (It was not purchased by DGS. So we don't know a detail of it.)

Noise measurement
After all PCIe cards were operated properly, noise level was measured for all ADC/DAC channels as shown in attached figures. Measurement configurations were completely same as ones in K1IX1 (klog#36586), K1IY1 (klog#36641), and K1EX0 (klog#36663). Measurement files were stored in /users/DGS/measurements/ADC/K1EY0/2026/0403_V2_IO_CHASSIS/.

RFM board replacement
When we were cleaning all stuffs up at the end of our work, we noticed RFM connection made an error bit. This was because a usage of wrong SFP modules single-mode or multi-mode. At the 1st floor of end stations, RFM fibers were laid by single mode fiber. On the other hand, the new V4 front-end computer which had been used as K1IY0 in the past had a multi-mode RFM board. So we moved single-mode RFM board from the old V3 front-end computer to the new V4 front-end computer and RFM connection came back online and GDS_TP screen showed all green. As the result, a remaining spare RFM board is multi-mode one.

Remaining concern
Only remaining concern is that it takes a few hours for synchronizing IRIG-B when a cold boot of the front-end computer is performed. In the past, similar things often occurred when down time became so long and a room temperature changed largely maybe because it took long time to be stable in the temperature of a crystal oscillator of timing slave. On the other hand, in this time, it takes long time even when a down time is only a few seconds. Such a thing wasn't reproduced in the test bench. So we have no idea to solve this issue now.

Fortunately, because this issue doesn't occur when the front-end computer is rebooted (there seems to be some difference between reboot and cold boot), we don't face this issue not so frequently. But reproducing and solving it on test bench is required from the view point of reducing a down time. If it's caused by the environment in the mine, we may need an additional test in the mine in stead of using test bench.