I have had a number of nights when the IR channel on the YALO imager produced huge variable warm pixel levels. The symptoms have not been seen at the telescope and I am writing this page to document the problem, so that the operators can easily see it.
 

My exposures have been typically 45s in JHK. Here is a normal J exposure taken on 8 March 2001.
This was plotted as:

display good.fits 1 zs- zr- z1=300 z2=5000

Here is a bad image taken on 19 March 2001 plotted at the same stretch. Notice the large number of warm pixels.
 

Here are some other diagnostic plots.

implot good.fits

implot bad.fits

imhist good.fits z1=-100 z2=10000

imhist bad.fits z1=-100 z2=10000

On 6/7 July 2001, I had the following image. This was the first J image in a sequence of JHK images.
There is clear ghosting on the chip. This ghosting disappeared over 10min or so. What I don't understand is that the previous images were taken some 20min before this one. This is the only case of ghosting I have seen and it really screws up the sky subtraction. This night also had variable warm pixels, although not as bad as above. The warm pixels appeared in the middle of a sequence of supernova exposures, right after the third 15arcsec offset, which seems to imply a problem with the electronics and not the coolant going off the detector.