Problem(s) Encountered:

During the TCS restart to resolve the dome encoder issue, the telescope moved on its own to the south in declination.  I hit the emergency stop button in the dome to halt the slew.  Manual slew was required to put the telescope back to the stow position. The telescope focus was found to be way off from previous nights even though the focus encoder reported the same value used the previous 3 nights.  Best focus before was 2660 but tonight that same value gave a big donut on the image.  After resetting the focus encoder by moving to the full-out position and setting to 0.0, we found the best focus at 1650 instead.  At the out limit, the focus encoder reported a value of 455.

Solutions:

This is a nasty bug in the system.  If the TCS control panel in the control room is powered on when the TCS computer is powered off (or disconnected due to a reboot), the telescope will start to move on its own.  (Perhaps it also moves focus?)  It’s critical therefore, to never power cycle the TCS computer when the TCS control panel is powered up (thus allowing power to the telescope).  Interestingly, this will occur even if the “Drives” toggle switch is powered off.  This implies that the problem is very low level in the TCS architecture.