MDM Trouble Report for 2007 Apr 25

Telescope: 2.4m
Observer(s): Sharma & Statler (Ohio Univ.)
Instrument: 8k camera

Problem(s) Encountered:
Telescope could not be focused. Problems started right away, while
doing twilight flat-fields. The focus encoder reading on the TCS
monitor did not change when the focus was adjusted with the paddle
or with the xtcs pulldown. We determined that the focus itself
was being changed, however, by looking at stars in our flat-field
images. The 1/0 indicators at the bottom of the TCS monitor
showed that the paddle button presses were being received by
TCS. We also found that we could reset the focus encoder
setting through xtcs. At that time the focus was not very far off. 
We restarted the tcs and xtcs programs but this didn't change
the problem. We then slewed to a bright star near zenith for
pointing. The focus encoder readings started changing rapidly
DURING the slew. When we took an image of the star, it was
completely out of focus. Evidently the focus itself was
changing on its own during the slew. We tried several slews of
various lengths, and saw that the focus encoder reading changed
during every slew. We did not, however, see a repeat of the
huge focus change that we saw in the first slew. Using the paddle and
successive images, we tried (after consultation with Bob)
focusing without the benefit of encoder reading. We could get
close but focus seemed not to be repeatable. We again consulted
with Bob, and on his advice rebooted the TCS computer, but
this didn't solve the problem either. We spent about an hour
more trying to focus, but this seemed always to be a moving
target, and we got the impression that the focus was in fact
changing on its own over time. At this point we gave up. We
noticed later that apparently the TCS reboot had resulted in
the TCS Declination being about 30 degrees off. We
didn't realize that the telescope was near zenith and partly
occulted by the dome, and so when we turned on work lights
in the dome to shut down we accidentally got bright light into
the guider cameras. We zeroed the tiltmeters and shut down
following regular procedures, and then again rebooted the TCS
computer, but the Dec encoder error is still there.

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Submitted on 2007 Apr 25 [22:52:41]