- There is no star in the autoguider field. Is the beam obscured?
Can you see anything through the telescope? Are mirror covers, dome and shutters
open. Did you provide the correct sky- or probe-coordinates of the guide star,
and are they within the limits (otherwise the probe
will not have been moved)? Is the probe in a sensible place? Has it
moved? (Use PFSTATUS to check this at Prime; Mimic display at Cassegrain).
Is the star visible on the finder in direct mode? If not,
then it may be too faint for the autoguider.
At Prime: Was the star close to the boundary of the box on the
finder? If so, it might actually be over the limits. Have you
gone back to BEAMSWITCH NOM? It sometimes happens that,
because of hysteresis in the finder, the guide star is out of
position in Declination. Try moving the probe by 50 in an
appropriate direction.
At Cassegrain: Is the probe within the unvignetted field of
the telescope?
- The autoguider selects the wrong star (e.g. a close double) when
there is an alternative and acceptable guide star in the field. Provide a
better position.
- Double-peaked or other non-Gaussian profiles. Is the star
double? (look on the finder!). If so, you probably cannot guide on
it. If both profiles are double-peaked or if a field integration
results in images with holes in their centres, then the autoguider and/or
the telescope itself is probably out of focus:
Ensure that the telescope is focused.
At Prime, refocus the guider using the ADAM commands GDFOCPOS and SETGDFOCUS.
Refer to section 
.
At Cassegrain, call for help.
Asymmetries in the profiles often result when the autoguider does a
scan before an acquisition movement has quite finished. This is nothing to
worry about; guiding should not be affected.
- The autoguider seizes up whilst guiding.
Press SHUTDOWN to re-initialise the autoguider, and repeat the
acquisition sequence, but make sure that the telescope, not the probe,
is moved during acquisition by first typing at the User Interface console:
AC/TEL
Assuming that the telescope has not drifted by more than
a few arcseconds, the object should be returned to exactly the same
position on the detector and observing can continue.
- The autoguider refuses to acquire by moving the probes. Have
you asked the probe to go somewhere illegal (is it close to a limit)?
Is the interprocessor link active on both computers? If not, try
reloading it (see chapter ).
- The autoguider or A&G panels do not respond. Refer to chapter
.
- At Prime: the Grinnell is re-initialised during normal operation,
e.g. by pressing the RESET button by accident. In this
case, the Prime-Focus overlay may not appear because the Grinnell thinks
that the Cassegrain system is required. To fix this, type:
RESETTV
- At prime: if acquisition of a guide star fails while everything seems to
work properly, check whether the TV finder scale has been altered (e.g.
by replacement of the TV camera). Nominal values
are 3.38 arcsec/pixel in x and 2.75 arcsec/pixel in y. In order to
alter the TV scale values type at the ADAM terminal:
TV\?SETSCALE
and follow the prompts. Alternatively, it may be necessary to measure the
scale anew: refer to section .
