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[Xu Sun <sunxuhit AT gmail.com>]

Hi All,

We have completed the ABC board replacement for Disk 1 Module 12, unfortunately, this didn't fix the problem of current fluctuations.

We have done the following to diagnose the issue:

1: swap ABC 42 (the one we suspect with fluctuation issue) with ABC 14, the same u207 HV channel shows current fluctuation and trips at 100 V.

2. swap HV channel u207 with u205 (on the same ISEG) to check the ISEG module itself. After swapping, u205 starts fluctuating and trips the HV channel. This suggests the ISEG module is fine and the issue is downstream.

3. to further confirm, we swapped the gray cable on the same ABC 14. After the swapping, u205 connects to Disk 1 module 12 outer sector and u207 connects to Disk 1 module 11 outer sector. u205 fluctuates and trips again, which confirms the issue is downstream.

The issue could be on the gray cable, PPB, purple cable or module itself. We cannot investigate/fix the issue without opening the pole tip and have access to the FST.

The module was running at 80V yesterday and was quite stable.

I would propose we run this module at 80V for the outer sector from now.

Best,

Xu and Yu