MDM Trouble Report for 2009 Jan 31

Telescope: 2.4m
Observer(s): McGreer / Stanonik (Columbia)
Instrument: CCDS

Problem(s) Encountered:

This trouble report is nearly identical to that of two nights
ago.  Upon opening, we pointed to a bright star near zenith
and set the encoders.  We then slewed to a target that was 3
hours west, but only 10 degrees south, and at a relatively low
airmass (~1.3).  When the telescope stopped, it reported that it
was pointing near zenith still, and nowhere near the requested
coordinate.  We went into the dome and saw that the telescope
was pointing NW and at the soft limits.  After returning it to
zenith and resetting the encoders it operated normally for the
next few hours.

Around 2am, we moved a fairly short distance between targets
pointing about 1 hour east, and the telescope would not track
correctly, as on previous nights.  Even after several minutes
it would not reach the requested coordinate, and as before we
could see that the hour angle was always behind the HA of the
next object, and not catching up.  As before, we tried moving
short distances to nearby stars and returning, and had some
success at getting it to eventually settle on a position.

After several iterations of this, we went to a target and the
telescope held position for several minutes without guiding
while we did some lamp exposures.  We then started guiding
and began a long integration.  After about 10 minutes, the
telescope began moving east and we lost guiding.  After several
attempts to return to the original position failed, we moved
to zenith and started over.  From this point on, we were never
able to have the telescope remain fixed on a position.  We
tried slewing by hand, then moving to stars, etc., and every
time it would continue to drift east and not reach the position.
The drift was usually stayed within a minute of the desired
position, but without catching up.  If we switched tracking off,
the RA would increase more rapidly, then when we turned it on
it would increase slowly, but not stop.

We rebooted the TCS while at zenith and continued to have the
same problems.  We noted that the track rate was set to 15.002
whereas previously it was at 15.07, so we changed it to the
latter value, but that did not help.  We noted that rate correction
was not enabled, so we enabled it, but that did not help.
Finally, thinking that perhaps there was some problem with the
drive motors, we parked the telescope at zenith and shut down
the drives for an hour.  When we returned, the problems continued
and we were never able to remain fixed on a position.

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Submitted on 2009 Feb 1 [4:58:29]