keita.kawabe@LIGO.ORG - posted 16:48, Friday 02 March 2012 - last comment - 20:09, Friday 02 March 2012(2345)
TMSY ISC in-vac components
Present status of ISC in-vac components on TMS are:
- QPDs work. This is important.
- Beam diverter itself works, but one of reed switches are stuck closed (ON). We will try to shim the sensor to push it far away from the magnet.
- One picomotor doesn't work (M1 Hor, this is the splitter for the green QPD and main path). This is likely the failure of the cable on the vacuum feedthrough (D1000223). Replacing this one is possible.
PZT cable woe.
First look at picomotor wiring diagram, D1100670 page 3.
Yesterday, I and Dan Hoak confirmed that 3 of 6 picomotors didn't work. We disconnected all mighty mouse connectors on the ISC table, and measured the resistance between all of the pins on DB25 cable from outside (i.e. after the mock feedthrough) using a volt meter, so that we were testing three sections of cables (D1000238, D1000921, D1000223) in series.
We've found that 1, 7, 8 and 13 were short-circuited (corresponding to pin 13, 7, 6 and 1 in-vac), and this exactly corresponded to the non-working picomotors.
Today I and Rodney disconnected DB25 on the ISC table, so that we were testing two sections of cables (D1000921, D1000223) in series. Pin 13, 7, 6 and 1 in-vac were still short-circuited.
Then I wanted to disconnect D1000921 and D1000223 so that I can test D1000223 alone, and even before I disconnected anything, as soon as I touched and wiggled the cables on the cable bracket on ISI table, something happened, and we broke one short circuit. Pin 1 and 13 were still connected, pin 6 and 7 too, but these two groups were not connected any more.
I disconnected the cable and Rodney tested D1000223 alone, and pin 6 and 7 were not connected any more, but pin 1 and 13 were still short-circuited.
The pins of the connectors looked fine (look pictures, male (sorry it's blurry) is on D1000921 and female is on D1000223). I dismantled the connector shell on D1000921 thinking that probably I can expose the wires at the back of the pins, but I couldn't because the shield was already firmly climped to the shell (third picture). Anyway, I took out the unused pins (they're useless and make it harder to reconnect).
When I connected D1000921 and D1000223 back together, pin 6 and 7 were not connected any more. WTH? The only difference is that I didn't use much force when assembling the connector shell, and when connecting two connectors.
One explanation is that the insulation of the wires are removed too much or something in the connector shell. If you look at the third picture again, you'll notice that some pins are sticking out much more than the others. Because the back of the wires are firmly bundled together by the climping of the shield, depending on how firmly you press the pins by the PEEK material when you assemble the shell, the wires in the shell could bend differently, making some wires contact with each other.
Anyway, this means that two more picomotors are working now, and we have only one non-functional picomotor. This in itself is not tragic, but it is tragic that we have cable failure which apparently depends on how I touch cables and how I assemble the shells.
It's not clear if the initial failure of pin 6 and 7 was due to D1000921 or D1000223, but we definitely know that pin 1 and 13 is due to D1000223.
Beam diverter cable woe
Look at page 4 of the wiring diagram. Same story here. Even though it doesn't affect the functionality of the beam diverter, pin 1 and pin 23 in-vac are short-circuited.
Then we started to disconnect things, and when I touched the connection of D1000921 and D1000223, something happened, and no short-circuit any more.
Just for completeness, I disconnected it anyway, didn't find anything (picture 4 and 5), and reconnected them again, fixed it on the bracket, and pin 1 and 23 are short-circuited again. Too bad.
List of bad (and potentially bad) cables
For the record, the serial number of bad cables are:
Replacement of S1104079
The only non-functioning picomotor, M1, is used for the steering mirror splitting the green main and the green QPD path. Replacing S1104079, we'll likely regain this important picomotor.
Regardless of this, we might lose M4 again in the future, but this is not critical for one arm test as it is only used for red QPDs.