K. Venkateswara, J. Warner
The BRS damper (see 14388) has been malfunctioning since yesterday afternoon. It's controller is an open loop system that assumes it is in the centered position when it is first started. Occasionally it can get restarted accidentally when the insulation box is bumped (probably due to a short somewhere, but I'm not sure where). It looks like this happened yesterday around noon.
This requires a manual re-centering of the turn-table for the feedback system to work as designed. I've attached the directions to do this. Jim will do this later today or tomorrow.
I checked on the BRS this morning, and found the code frozen. I followed Krishna's fairly straightforward document up to the point of opening the box and found the masses 90 degrees out of position (NW/SE instead of SW/NE), I was unsure of what to do, so I closed up, restarted the code and called Krishna to consult.
Afterwards, I went back to EX this afternoon, and re-aligned the masses on the damper. I did this by first modifying the code as described in Krishna's document, then opening the large insulating panel on the west side of the BRS enclosure, and just turned the turn table until the masses were approximately SW/NE. The turn table moved quite easily, I was expecting more resistance.It was dark down there, so it was hard to get a good picture, but I've attached an image taken from the west side of the BRS enclosure, showing how I left the masses. I then went back to the rack, re-commenting the appropriate code and restarting. Haven't had a chance to check on the BRS since then, but it looked okay from what I could see on the laptop readouts.
Looking back at the data, it seems that the changes made in the morning, resulted in a positive feedabck loop leading to large amplitude oscillations in the BRS. The changes made in the afternoon reversed it but it took ~5-6 hours to damp. However, the software appears to have crashed again later. Tomorrow, I'll investigate for intermittent shorts or other grounding issues.