Problem(s) Encountered:

TCS GUI  Telescope Position  readout shows the telescope tracking (HA

increasing, RA constant), even after switching Tracking Rate for HA to 0. Flipping the  Track  switch in the computer room to  Down  had no effect. Other symptom: TCS does not accept new coordinates from JSkyCalc24m.

Solutions:

It’s possible that this condition is triggered when a slew is commanded to a new target while the HA track rate is set to zero. The observers accidentally reproduced the condition this way during morning twilight.

Restart the TCS:  Write down the dome Azimuth.  On the control room rack, set the  Track  switch to  Down. Quit the TCS GUI: File -> Exit.  Double click the yellow TCS icon to restart the software.  Telescope --> Initialization --> Other Positions. Enter the dome azimuth, click  Apply. (At this stage the  Other Positions  window contains a warning to make sure the dome is switched off: that can be checked by going to Telescope --> Misc --> Switches; the dome should already be set to OFF.)  Telescope --> Misc --> Switches. Switch the dome ON and make the dome target Telescope. Hit Apply.  Flip the Track  switch in the computer room to  up.  Check that the HA is not changing (since the HA rate should still be zero).  Telescope --> Rates --> Track Rates. Set Sidereal Rate, hit Apply.  By this point the telescope should be tracking again.