No Light Visible From Cal Lamps and/or AO Fiber

Symptoms:

Very occasionally, there will be no light visible on the SPEC detector in any kind of calibration lamp image, at any reasonable exposure time. An unrelated problem, but one which may appear at first to be similar is the lack of light from the AO fiber on the SCAM detector.

Diagnosis:

Take a short (1-2 sec) SCAM image with the flat lamp on. Look for a critically-sampled (about 2 pix wide) bright spot a little bit off-center, and not on the slit. This spot indicates that the Calibration Unit pinhole mask has for some reason ended up in the beam.

If the problem does not appear to be due to the pinhole, and NIRSPEC is behind AO, its possible that filter wheel 1 has moved. When behind AO, filter wheel 1 is set so the AO pupil stop is in the beam and should never be moved. The most common way it can get moved is if an observer loads a non-AO setup script. A sufficient (but not necessary) indication this is the problem is that the filter indicated by XNIRSPEC does not have a -AO suffix.

Cures:

The cures for both problems requires running scripts from a waimea command line. Go to any command line window with a waimea prompt. If you don't have one open already, go to the blue background, hold down the right mouse button to get the general menu, scroll right to enter the first submenu Login Windows, and select the SECOND entry in the submenu, xgterm 'waimea' (NIRSPEC).

If the pinhole is the problem enter the command:

• pinholeout

If filter wheel 1 is the problem and NIRSPEC is behind AO enter the command:

• set_ao_pupil

Discussion:

The cal unit pinhole mask has no home position switch. The only way to "home" it is to force it to move a large number of motor steps in the negative direction, then to set the keyword flag that tells the software the mechanism is "at home." The motor initialization script that is run as part of the startup sequence does this automatically, but for some unknown reason it doesn't work about 1 time out of 100. If it fails, the easiest cure is just to run through the process again, which is what the pinholeout command does.

Note that a SCAM image of the slit plane is very helpful in diagnosing problems with the cal lamps. When lamps are on, you should see a bright illuminated circle that covers the majority of the SCAM field of view. If you see only the small spot, that confirms that the pinhole is in the light path of the lamps.