Troubleshooting guide

VIII.Troubleshooting
1) Problem: The image looks funny. You can see all 32 amplifiers, and the signal level is ~58,000 ADU; the
preceeding or following image(s) has 0 counts.
Solution: This is a hardware problem related to electrical noise causing an early readout of the detector. In
imaging mode MCE4 reads the array once, and then lets it integrate before reading it again (cf. Appendix 2:
Readout Schematic). The final image written to disk is the difference of these two images. This problem occurs
when MCE4 spits out the image before making the second read and difference. There is nothing you can do to
resolve the problem.
Typically, we get bad reads for about 2-5% of the images taken for exposure times ≤ 60 seconds. If you are
getting a much higher failure rate you should call for help
You should be cautious with the image immediately following a bad read frame, because the ADU level in the
image is frequently lower than it should be.
Recently we found that if you get more than two zero frames in a row, then the MCE4 array controller needs to
be rebooted and reinitialized. See the solution to item 4a of the troubleshooting guide for how to do this. N.B.:
the first image taken immediately after rebooting MCE4 also looks like a bad read.
2) Problem: The image looks funny. Various bits of it are scrambled or not in the correct position, or some
bits of it are completely black (0 ADU).
Solution: See if the next image looks normal, if it does keep taking data. If the next image is similarly messed
up, then the MCE4 array controller needs to be rebooted. See the solution to item 4a for how to do this.
3) Problem: Excess Background
Possible solutions:
a) Image a very bright star (V ~ 2) at K
s
-band, with the telescope way out of focus, say 2000 units lower.
You should see a donut with a central obscuration and spider vanes. If it's not circular, then you could have
something obscuring the beam---e.g., the dome, the mirror covers, or a mispositioned filter, lyot stop, or Grism
wheel.
b) Check that the ion gauge on the Granville-Phillips pressure monitor is off. When left on it casts a
large amount of warm illumination on the lower right hand corner of the array.
c) Check that the MOS dewar temperature is lower than 200 K. If the temperature is not between 80 – 95
K, did you forget to fill the dewar with LN
2
? What about the camera dewar?
4) Various Problems related to image readout, wheel motion and iocomm communication.
The three daemons started by initflam.pl (temperature, motor, and MCE4) work by issuing commands to
particular hardware addresses on a networked device called the perle (this used to be the iocomm, but it was
replaced by the perle). This device is like a multiplexer. We have three devices (the temperature monitor, the
FLAMINGOS@4-m, Ver. 2.34, 2006 Apr 04 Page 32 of 44