We tested the trans impedance switches of the old L1 OMC which was used in H1 squeezing (old H1 OMC is at LLO) because we'll reuse the electronics, and because, during the squeezing test, the trans impedance was stuck at 400 Ohm.

Back then we observed (without opening HAM6 chamber) that one of the z-switch pin was somehow short-circuited to the bias voltage pin somewhere inside the chamber, thus energizing the relays. We assumed that the short circuit is on the in-vac cables connecting the vacuum feed through and the OMC cable bracket, i.e. not on the part that is on/inside the OMC cage, but we never confirmed that that was the case.

Today we connected the OMC, still in the suspension cage, to the dummy flange using a class A DB25 cable, then connected the dummy flange to the OMC whitening box (D070281) via a dirty DB25 and a break out board.

We used a Stinger flashlight which caused the in-vac whitening output to jump to about 0.5V.

When we connected 5V power supply to the trans impedance relay input and the ground on the out-of-vac side (pin17=+5V and pin16=GND for PD1, pin21=+5V and pin20=GND for PD2), we were able to hear the relay clicking, and the output of the in-vac whitening became about 2V.

So, everything is working fine, whatever trouble we had in squeezing is the in-vac cable failure, and we can reuse the electronics.