Please check the FILLING CCD DEWARS section for instructions on filling the 4shooter dewar.
If you begin to see elevated background counts and you are not pointing at the Moon, that may be a sign that the CCDs are warming up. You should first confirm the diagnostic by taking a few biases and comparing their levels with earlier good biases. Bias levels higher than normal would confirm the diagnostic. If the problem persists, the final diagnostic may be found here for Minicam.
OBSOLETE SECTION FOR 4SHOOTER (ignore for Minicam):
The red LEDs at the top of the 4shooter dewar (on the ion pump) are
the readout of a pressure gauge,
in the form of a
bar graph that reflects the quality of the vacuum in the dewar and
the temperature of the CCDs. If about 7 of 10 of the LEDs are on,
the vacuum is about 10^{-6} Torr and the temperature of the chip is
-100 C or colder, the normal state. If you do have a dewar problem,
the state will probably not be normal.
If the LEDs are all on or blinking, the CCDs may have started to warm up due to a loss of vacuum. If you caught the problem sufficiently early, filling the dewar may be the cure. Once the dewar is filled, check the LEDs. If the display is not blinking and back to the normal state, it's probably OK. Unfortunately, the LED readout is notoriously sensitive to the state of the connection of its wires. If you are not back to the normal state, sometimes removing power by unplugging the ion pump momentarily and plugging it back in restores operation of the readout. If you do get to the normal state, take more biases to confirm a return to normalcy.
If after a few minutes the LEDs still blink, call for assistance (click here for telephone numbers). Pumping and oxygen flooding may be required; this is a long process. If you have reached this point, you probably have lost at least one night. You should seriously consider whether to have staff come back to the mountain during the night, or whether to wait until they are back at the Ridge in the morning. Also, consult with the 1.5m observer.