In General No guide stars, bad pointing The TCS disconnects The WFC disconnects Shutter problems Filter wheel problems Data Acquisition problems Pickup noise from autoguider of +/- 10 counts In General Most of the faults can be cleared by typing: SYS> startobssys Try to avoid 'shutdownobssys' followed by 'startobssys' as in most cases such a drastic measure isn't needed. SYS> shutdownobssys should only be used to shutdown the observing system at the end of the night. If a sub-system (DAS, TCS or Autoguider) is corrupted 'shutdownobssys' wont help. First the sub-system has to be brought back, then SYS> startobssys will re-establish contact between the observing system and the sub-systems. No guide stars, bad pointing First repeat ZEROSET at zenith in engineering mode followed by: USER> CAL LAST Check pointing with a pointing grid star and the autoguider: USER> GOCAT pointing-star USER> AP 5 mark the autoguider window center (SETUP/TOGGLE CENTER CROSS) SYS> agwin acq pos 1032 512 SYS> autotv on If the star comes up within 15 arcsec from the center, the pointing is fine. If no bright star is seen may be the last pointing solution is wrong or got corrupted somehow. Before calling for help try this: Repeat ZEROSET at zenith in engineering mode followed by: USER> CAL DEFAULT and check again the pointing with a pointing grid star and the autoguider. To recalibrate the telescope pointing follow this commands. The TCS disconnects Most likely the TCS TELD task has died. To restart go to the xterminal were the TCS user interface and info display are running. Open a LAT terminal and log on to lpas2 (see label on screen for uid and passwd). From the main menu then select 'options' and 'teld' from the options menu, afterwards SYS> startobssys will re-establish contact between the observing system and the TCS. The WFC disconnects If WFC disconnects, as shown by the orange warning-label on the mimic, the DAS has probably crashed. Check the orange telnet window that's logged on to the DAS (lpss14). If not available you have to start a new telnet connection to lpss14 from the background. Run first 'obssys' with the actual option first in order to get the DAS> prompt. Type return to see if there is a termination message for udas_server (the WFC task is an instance of the udas_server program). If udas_server has stopped running, do this: 1. Type startobssys at the DAS> prompt. 2. Watch the talker. Wait until you have seen WFC come on-line. 3. Type startobssys at the SYS> prompt. 4. Wait for the mimic to reconnect to WFC. Shutter problems It happens when you start an exposure that you get the message 'The shutter failed to open at the start of the exposure' (red/blinking/beeping). Simply quit the alarm and repeat the last command in this case. Elapsed time is counted in a blue box on the GUI while the shutter is open. After the read out the box turns to green. There is a fault when the box goes orange with time elapsed=0. The exposure is logged with 0 seconds exposure time or not quoted at all in the observations log and in the headers. The fault has to do with the MCA controller. To recover type: SYS> cmd MCA RESET With the next exposure the exposure time should be recorded correctly again. If this doesn't help bring the telescope to access park and power cycle the MCA controller, this is the controller on the bottom of the WFC assembly (rotator at 180 deg.), followed by: SYS> cmd MCA RESET Filter wheel problems On WFC startup, it is NOT uncommon for the MCA controller (the electronics rack mounted on the WFC which drives the shutter and filter wheel), to have problems identifying the filters which are loaded. In this case, it may be necessary to send the command: SYS> cmd MCA RESET When changing filter-position you might get the message 'The filter-wheel detent pin is malfunctioning' (red/blinking/beeping) or 'filter wheel movement timed out'. Simply quit the alarm and repeat the filter command if this happens. If this doesn't help bring the telescope to access park and power cycle the MCA controller, followed by: SYS> cmd MCA RESET Data acquisition problems By Data acquisition we mean the management of an exposure, reading of data from the CCDs and saving to disk. This may fail in one of several stages, for example: Run, Finish, Abort or Re-time commands are not successful Run process stops after CCD clearing Run spontaneously aborts during readout or transfer to disk Transfer to disk does not complete to 100% Data on disk is corrupted (e.g. torn frames) These may or may not be accompanied by a pop-up error box/alarm. If the error pop-up mentions the (ultra)DAS or "reset the camera", and you cannot continue observing, then the following procedure is recommended (pink window): SYS>dasreset WFC            (i.e. startobssys is unnecessary, unlike in e.g. WFC fault) When this completes, try a new Run and see if the above fault recurs. If it does, then a lower-level reset of the CCD controller may necessary and you need to move the telescope to access park. Power cycle the unit labeled SDSU CCD controller, located to the left of the cryostat, followed by: SYS>dasreset WFC Pickup noise from autoguider of +/- 10 counts The problem is pickup noise from the autoguider on chip 1 and 4. So if the autoguider is off no noise patterns are seen. The magnitude of the effect is +/- 10cts. Using signal we estimate that for typical exposure times (5min.) poisson noise from sky is higher than this effect (in U we get 122 photons/pix). This effect shouldn't be a killer for most science exposures. However narrow band / U imaging of faint extend objets might suffer. The workaround is to stop guiding when reading out, this can be done by typing: SYS>guide off when the ccd starts to read. A more simple procedure is to include in your script the following comand: SYS>run 500 object & SYS>udas_detect_ro WFC; guide off This will ensure that when you are taking the exposure, as soon as reading starts the autoguider is turned off. If you are unsure about any of the recovery procedures or if they fail, call for WHT TO, SA or DT/IO support.