Troubleshooting

 If the above tests are not successful, either the instrument was assembled incorrectly, or a piece of the system is not working properly. Possibilities, in increasing order of complexity, include:

$\bullet$ The calibration lamp is not on.

This should be obvious. The Neon lamp is bright enough that it will clearly illuminate the 60-inch dome or the 200-inch flatfield with an orange light. The Hydrogen lamp will provide a pale blue-violet light. If you are still unsure whether the lamp is on, try taking a longer exposure, an exposure without a filter in the telescope beam, or a short exposure with the flatlamp on, to be sure that the CCD is working properly.

$\bullet$ The telescope cover is on.

Again, this should be obvious. It is easier to forget than you might think...

$\bullet$ The wrong filter is being used.

If the wrong narrow-band filter has been used, you may not see any rings at all. Try removing the filter from the optical path and taking another exposure. You may then see the emission lines, although probably only weakly. Verify the identity of the filter. If you are using the Neon filter, and you have reason to believe that it may be in the wrong holder, carefully remove the filter from the holder and verify that the identification code on the edge of the filter glass is ``ANDV1844''.

$\bullet$ The etalon parallelism is very bad.

If this is the case, the system should show more counts with the dome lights on, and there will probably be some nonuniformities in the illumination. Look at the Fabry-Perot controller to confirm that the green operate light is on rather than the red out of balance light. If this is ok, and the controller knobs have not been adjusted (other than described above), this is most likely not the problem. If the controller is out of balance, switch the operate/balance knob to balance, then back to operate. If the controller still will not balance the etalon, try switching the operate/balance knob to balance, cycling the controller power, then switching back to operate.

$\bullet$ The calibration rings appear blurred.

This can be due either to a problem with the etalon parallelism or to the camera focus. Generally you can distinguish between these because an etalon problem will affect all of the rings, with a distortion that is inversely proportional to the radius of the ring, whereas a focus problem will be most evident in the narrower outer rings. See either ``The etalon parallelism is very bad.'', ``The calibration rings are doubled.'', or ``The camera is far out of focus.'' for more details.

$\bullet$ The calibration rings appear doubled.

First, follow the procedure in ``The etalon parallelism is very bad.'', above. If this does not work, suspect 60 Hz interference. The 60-inch telescope in particular has a bad ground-loop problem. Try disconnecting the RS-232 cable from the CS-100 to see if this fixes the problem; if it does, then probably the RS-232 shield wire is not connected.

$\bullet$ The CCD is not working.

If no excess counts are seen in an exposure taken with the dome lights on, it is likely that the CCD is not working properly. First check that the bias level is reasonable in the 0-second exposure. This should provide you with an estimate of the background level of the CCD. An exposure taken with the dome lights on should raise this level, especially if the telescope/mirror cover has been removed. If not, you may need the help of the Palomar staff to get the CCD working.

$\bullet$ The shutter did not open.

This can be verified by taking another exposure while listening; the clicking of the shutter should be evident from the speaker connected to the dome. As discussed above, the ``big shutter'' is used on the 60-inch telescope. You will therefore need the assistance of the mountain staff to debug this problem.

At the 200-inch telescope, however, the internal Fabry-Perot shutter is used. In this case, you should first recheck all connections between the Fabry-Perot shutter and its electronics box. If the shutter still does not appear to be working, try to monitor its operation by looking through the shutter control cable hole in the side of the instrument tube. You may be able to insert your finger in this hole as well, to monitor the movement of the shutter mechanism directly. You may find the ccdopen and ccdclose commands useful for testing. If necessary, you may want to gradually raise the voltage supply to the shutter by turning the dial on the variable power supply. Do so with care, however, to be sure that the shutter controller is not overloaded. You may want to ask the Palomar crew to verify the electrical signal on the BNC control line as well, and check that the shutter polarity switch is in the ``up'' position.

$\bullet$ The camera is far out of focus.

If the system shows more counts with the dome lights on and there are nonuniformities in the illumination, this may be the culprit. The next step will be to focus the camera, but you may want to adjust the focus now and take another exposure, to see if the illumination pattern changes. Unfortunately, if this is the problem, then the camera focus ring was probably not properly positioned on the camera lens (i.e., Figure 4). The shutter control box, dewar, and camera lens plate will need to be removed to rectify this problem.

$\bullet$ The optical path is obstructed.

If the shutter is operational, but you still do not detect any light through the instrument, there may be another obstruction in the light path, such as the lens cap on the camera lens or collimator. Unfortunately, you will probably have to remove at least a portion of the instrument from the telescope and disassemble it in order to find the obstruction.