Non-final podded seismometers were being used for testing on our completed HAM assembly. Last week a horizontal unit wasn't functioning correctly, it would respond to large inputs but damp very quickly. I thought this would most likely be caused by a mass that was uncentered. Luckily for us this particular seismometer was going back to Livingston anyway, so Vincent and I popped the vacuum pod and removed the GS-13. While doing this I noticed the crossbar on one edge was noticeably looser than the others and was most likely due to a kinematic foot backing up the threaded rod. This tilt would be enough to rail the seismometer's mass.

While the can was off the base plate Vincent and I double checked the flexures to see if any of them had loosened or broken, but they were all in good shape. Since we don't have an angle bracket to re-level the horizontal GS-13s to the base plate I hoped that the top of the seismometer was perpendicular enough to the mass to level from that. With the GS-13 back on the base plate and a precision level on top of the GS-13 I adjusted the kinematic feet to obtain a level (again hopefully perpendicular) within 80-90 seconds. Then I locked down the jam nuts and hand tightened the crossbars. After sealing the top hat back onto the base plate I realized I probably should have taken pictures, then I freaked out and wondered if I unlocked the mass. After reinstalling the pod onto HAM 1 Vincent checked the refurbished GS-13's frequency response to the others and everything looked good.

This definitely seemed to be an issue with either a loose jam nut or an insufficiently tightened crossbar. These testing seismometers saw quite a bit of abuse with how much they had been removed and reinstalled but extra care should be paid attention to these feet as having to deal with a bad GS-13 in vacuum will be a significantly larger headache.