Patrick T., Thomas V. Last night Thomas and I swapped the temporary cables being used to test the rotation stage in the CSR with the ones made for the final installation. These are not pulled yet, but are coiled in front of the rack holding the Beckhoff PSL environmental chassis and attached to a rotation stage sitting on a rolling table nearby. For some reason two cables had been unplugged from the controller box (goes between rotation stage and Beckhoff module). One was power and the other was a control cable. I'm not sure why they were unplugged, but we reattached them. I was hoping this would address problems we were having getting the rotation stage to move, but they have persisted.
The "failure" of the Newport URS50BCC rotation stage was of concern to me as we have three of them in each IFO controlling significant amounts of laser power. These were new units and we had been reasonably careful with them. Why should this one die all of a sudden? This is what I found on investigating our broken rotation stage, S/N B12 6940 (Newport's serial number, not the ICS or DCC number).
The rotation stage's angular encoder was working. The TwinCAT2 control software for the rotation stage was showing angle and the "Mechanicsl Zero" signal was present (a high to low transition on moving from 350 deg to 5 deg). This indicated that the electonics was working and not blown. However, the resistance across the motor terminals (at the DB15 connector, pins 2 and 10) was infinite. Opening the housing that held the DB15 connector and printed circuit while monitoring the motor resistance, I found that it would intermitantly read 57.4 ohms, the proper motor resistance. The problem was traced to a bad connection of the upper ribbon cable which went from the printed circuit board to the motor and shaft angle encoder. The connection was a leaded connector designed for through-hole mounting and soldered onto surface-mounting pads. This is not a method of assembly I would recommend. I patched it back together and confirmed that the stage works. I'll use this for debugging and testing and assign it to our spares.