Abstract
- PR3 and PRM was down at 6:41 because the power supply as DC -18V was tripped.
- We wasn't able to identify the broken circuit.
- After recovering all circuits, the power supply unit was tripped again.
- All circuits were turned OFF tonight for safety.
Details
In this morning, we noticed that all ADC channels on PR3 and PRM became digital zero.
At first, I thought it's problem only on PR3, So I guessed this was the software problem and restarted k1vispr3t and k1vispr3p.
However they were not recovered by restarting.
Note: I forgot to check the SDF of PR3 models before restarting. So I need to check all the set point values to recover the alignment.
After entering mine, I found that the power supply as DC-18V was tripped.
So we turned OFF all circuits in PR3 and PRM racks once.
The power supply unit was turned ON after breaker switches were also turned OFF,
At this time, the power supply unit seemed to work well (output voltage was surely -18V and no error indicator was light up).
As the next step, we turned ON each circuit one-by-one in order to identify broken circuits.
But all circuits was able to be turned ON in properly. Both +18V and -18V indicator on the rear panel was light up.
Finally, PR3 and PRM racks were able to be recovered once.
After the recovery real-time models worked well for a while (~30min).
But the power supply unit was tripped again.
For the IMC closing work, we recovered only PRM rack again and it worked well roughly 3.5hrs.
We planned to keep this situation tonight. But unfortunately we found the power supply unit was tripped again after IMC works.
For safety, we finally turned OFF all circuits in PR3 and PRM racks.