Marc, Oli, Jeff, Jenne, Richard, Betsy, Fil, Keita, Rahul

Yesterday afternoon, Jenne pointed it to us that she was struggling to point (move in pitch or yaw) MC2 suspension in HAM3 chamber - she was applying bias on Pitch dof and was not seeing optic move accordingly (this was to get the beam in HAM2 for ISS PD work). We then started troubleshooting  MC2. We started with the usual health checks (trying to damp the sus, TF measurements, M1 osem spectra) and it clearly looked that something was off - though we were not able to pin point on anything. Fil and I then swapped the cable 01 with cable 02 (basically trying to run MC2 using PR2 electronic chain for T1, T2, T2 and LF bosem - for ref. see wiring diagram D2300383, page 01 for MC2). When we (Oli and I) tried controlling MC2 using this, the results were all the more confusing.

This morning I restored the MC2 and PR2 cables back to its nominal state. Marc and I then started looking into the electronics chain of MC2 - poking each stage one by one. We started at Satamps (in the LVEA near HAM3 chamber) where I applied some offset at the CD on the medm screen and Marc measured the output voltage. For bosems T1, T2, T3, LF we measured 230mV and for RT and SD (these two bosems on MC2 share the electronics chain with PR2) we measured 350mV. We then moved to CER and repeated the same measurement at the MC2 coil driver and the result was no different. To check the DAC card and AI chassis we routed MC2 through another Coil driver (used by PR2) and yet there was no change in the output voltage. We swapped out the satamps and coil drivers to look for any change - found none. This meant that the electronics chain for MC2 was  healthy, hence we restored everything.

Richard then suggested to measure the resistance of the coils on the BOSEMs at the satamps. For T1, T2, T3 and LF it was found to be around 16 ohms (much lower than what we expect) and for RT and SD 40ohms (which is the correct value). Around lunch time Marc and I talked to Jeff kissel and everything at this point was pointing towards the suspension (either the bosems or their connection at the new feed through) in Ham3 chamber. After lunch time Marc and I headed to HAM3 chamber. After looking at the dust count (measured in lower 10s), I opened the curtains on the +Y side near MC2. I then identified the M1, M2 and M3 stage cable on MC2 and followed it to the connector on the ISI table. I then followed the table cable to the feedthrough connection (in vacuum side). Marc was standing outside the chamber near the feedthrough side (in air). I then started unplugging the cables on each stage one by one and initially it was very confusing but very quickly we realized (to cut the long story short) that - the M1 and M2 stage cables were not correctly connected at the feedthrough (in vacuum side - see D1002874). To confirm this we measured the resistance of the bosem coils at the D6 feedthrough in HAM3 chamber. The top F1 and Bottom F3 connection were showing out 16 ohms and the middle F2 was showing 40ohms. This told us that the middle F2 connection belongs to the M1 stage and the top F2 belongs to M2 stage - see below for clarity.

Given below the flange layout in HAM3 chamber (D1002874)- D6 F1 and F2 were incorrectly connected. Marc and I changed that on in-air side.
Old connection - D6-F1 F DB25 SUS MC2 M1 T1T2T3LF OSEMs. New connection D6-F1 F DB25 SUS MC2 M2 OSEMs
Old connection - D6-F2 F DB25 SUS MC2 M2 OSEMs. New connection D6-F2 F DB25 SUS MC2 M1 T1T2T3LF OSEMs
Did not touch - D6-F3 F DB25 SUS MC2 M3 OSEMs

 Oli took transfer function measurements and will post the results below. In the meanwhile we can say that MC2 is healthy and back in action.