ON SITE: Flavio - Piernicola - Suzanne

FROM REMOTE : Ilaria

Today,  we performed the following tests in the TCS room to investigate the problems on the WI CO2 main laser initially described in 67976. Here the lists of the tests:

1. 5 V TTL modules swap
We powered off both lasers and swapped the BNC cables that provide the 5 V TTL enable signals: WI connected to the NI module and vice versa.
Result: the WI laser continued to show on/off events. Therefore, the 5 V TTL signal is not the cause.

Actions  timeline:

• NI OFF: 12:28:26 UTC

• WI OFF: 12:28:52 UTC

TTL swap back. Then, 

• NI ON: 12:29:21 UTC

• WI ON: 12:30:19 UTC

2. RF driver swap and inspection
After excluding the 5 V TTL as the cause, we swapped the RF driver generators between the two CO2 lasers.
NI OFF: 13.36.54 UTC
WI OFF: 13.37.11 UTC
RF signal generators swapped. Then,
WI ON: 13.38.00 UTC
NI ON: 13.38.30 UTC  

3. INSPECTION ON THE BENCH
During this test, Flavio, Piernicola, and Suzanne visually inspected the lower part of the enclosure where the RF driver is located. We noticed that the WI laser switches off and on when touching the cables connecting the power supply to the RF driver at the junction (see the attached figure).
At this point, Flavio temporarily secured the cables to keep the laser on while deciding the next steps.

Notes:

• The BNC connections of the RF generators are still swapped — to be RE-SWAPPED

• Even in this case, touching these cables and turning the laser on/off produces simultaneous disturbances on the PR CHRoCC (see the second figure).

Since the intervention, no further crises have been observed in the CO₂ laser behavior.

We will continue to monitor the situation. In the meantime, the electronics crew has prepared the needs for soldering the cables, so that the repair can be performed during tomorrow’s maintenance.

It goes without saying, but the RF driver is covered with mouse droppings.